Searching \ for 'led' in subject line. ()
Help us get a faster server
FAQ page: www.piclist.com/techref/displays.htm?key=led
Search entire site for: 'led'.

No exact or substring matches. trying for part
PICList Thread
'2.5 digit LED from Stamp?'
1995\07\16@031545 by David Baker

It appears the Stamp List has died? I thought I would post here & see how
it goes - I guess the Stamp people are still here, anxiously awaiting the
Stamp II.

We have an LCD display at work which the person using says is too small for
him to see. It is an LCD display hooked to the serial output of a computer.
It displays the depth of some sensors that are put into the ground & has to
read a maximum of 19.9 metres to 0.1 metre accuracy.

I figure the easiest way around this would be to hook a Stamp into the
serial line, collect the numbers & power some big (2 inch) LED 7 segment
displays. I thought I would run it through here for comments first. I have
played with these devices a bit but haven't gotten too technical yet. Some
points that come to mind:

7 segments x 2.5 digits means 16 I/O pins + 1 for the RS-232. Is there any
easy way of using less pins? If not I guess I need a Stamp stretcher as
well.

Can I run a 7 seg display directly from the Stamp or stretcher? The spec
sheet I have says 20 or 25 mA per pin but only 40 or 50 mA total! This
doesn't sound like much. Anyone recommend some good buffer chips?

How about programming space/speed? I can vary the baud rate down to 2400 or
1200 or even less if necessary I guess but there are some garbage
characters before the numbers that have to be discarded. Does anyone think
it's impossible to collect the characters, decode them & run 3 displays,
all in 256 bytes? I figure some sort of lookup table for each digit is in
order.

Why isn't the Stamp II out yet? Sure would make life easier!

Regards,

Dave

--
-------------------------------------------------------------------------
|       David Baker        |  Internet   ID (home) - spam_OUTdavidTakeThisOuTbaker.pc.my  |
|   Electronics Engineer   |  Internet   ID (work) - .....davidKILLspam@spam@gmetra.po.my |
|                          |  Fax                  - 60-3-2612870       |
|  Kuala Lumpur, Malaysia  |  Compuserve ID        - 70461,2360         |
-------------------------------------------------------------------------

1995\07\16@131556 by Bill Cornutt

----------
>It appears the Stamp List has died? I thought I would post here & see how
>it goes - I guess the Stamp people are still here, anxiously awaiting the
>Stamp II.
>
>We have an LCD display at work which the person using says is too small for
>him to see. It is an LCD display hooked to the serial output of a computer.
>It displays the depth of some sensors that are put into the ground & has to
>read a maximum of 19.9 metres to 0.1 metre accuracy.
>
>I figure the easiest way around this would be to hook a Stamp into the
>serial line, collect the numbers & power some big (2 inch) LED 7 segment
>displays. I thought I would run it through here for comments first. I have
>played with these devices a bit but haven't gotten too technical yet. Some
>points that come to mind:
>
>7 segments x 2.5 digits means 16 I/O pins + 1 for the RS-232. Is there any
>easy way of using less pins? If not I guess I need a Stamp stretcher as
>well.

A 7 segment display requires seven lines to drive the segments plus one for
the decimal point.  And three digits would take three lines to select
the digit.  Therefore it would take 11 lines in the conventional way.
AMD use to make a chip that would handle eight digits.  It has been
a long time sense I used it but I think you put the value on its pins
in parallel for each digit is order along with a clock.  Then the
chip would handle the decoding and multiplexing.  It took eight
parallel input lines and also two or three clock/control lines.
The good thing about this chip is  that it does the decoding,
multiplexing, and driving (buffering) of the display.

When not using any external chips, the seven segements could be
driven with seven lines using a npn transistor for each segment
and a pnp transistor for the digits (my solid state theory is
limitted, so you had better check to make sure that you wouldn't
draw too much current through the base of the transistors).  And
you could also hardwire the decimal point to save a i/o line.

You may have a brightness difference in the decimal point because
on its current not going through a segement transistor.  If this
is noticeable, then connect a driver to it and hardwire the input
to the driver so that it is always on.  Or stick a little diode
in its circuit to get the same voltage drop as a driver would have.

The CMOS chip 4049-4050 can both sink and source a lot of current,
so these may be a good ic to use for both segement and digit select.
Because they come in six packs (as do all good things), you would
need only two ic's.

The segments of the led will have to have a current limiting resistor
in the circuit so that too much current will not destroy the led.
This resistor should be placed in the driver circuit for each of
the seven segments, and the decimal point.

Again, my solid state theory is limited, but....
If you are using a 5v supply, then you could figure there is a 0.6v
drop across the segment driver, 0.6v drop across the led, and
a 0.6 volt drop across the digit select driver.  Therefore to
determine the value of current limiting resistor, use 3.2v as the
voltage across the resistor. (but I could be wrong, so check it out
first)

With more than one digit it is normal to multiplex them.  Because
of multiplexing, the current ratings for the led's gets complicated.
I think the specifications for led's may have two current ratings.
One is the "average max current" and the other is the "max current".

So the average current would be influenced by the oh/off time ratio.
Seems like the thing is multiplex at 60 times a secomd and multiplexing
8 segments (or eight digits if you turn on a common segment and then
select the digits have that segment), would give you a on time of
about 2 ms and a off time of 14ms.  And by putting more current
through the led (even if for a shorter time) our eyes see it as a
brighter display.

Again, the Advance Micro Devices chip handles all that for you.

And that is my opionion!

  ---------
  Bill Cornutt
  billcornKILLspaminfoserv.com
  Located in Ione California USA.
  A small town in Northern California.
  Sitting against the foothills of the Mother Lode.
  ----------------------------------------------------

1995\07\16@181258 by First Last

1995\07\16@185733 by William Chops Westfield

1995\07\17@015543 by Tom Mornini

1995\07\17@033727 by Neil Thomson

1995\07\17@174630 by Claus K|hnel

1995\07\18@142443 by Markus Imhof

1995\07\19@235301 by Stephen Kormilo

On Tue, 18 Jul 1995 20:24:10 +0100 you wrote:

Stuff deleted...

>I don't have the databooks here, but in the standard 74 series, there are
>lots of LED-display drivers, including BCD-to-7-segment decoders (which
>will bring you down to 6 lines - three for the BCD code and three for the
>digit selection).
>
>Bye
>  Markus

BCD code requires 4 lines, on the other hand, addressing 2.5 digits would
require only 2 lines, so only 6 lines are required, but not in the manner
indicated.

In addition to the BCD-to-7 Segment Decoder, a Digit driver (2 line to one of
four demultiplexer) chip would be required.  It's the usual tradeoff, more
external hardware makes it 'easier' on the micro (fewer connections & simpler
software), but the system becomes larger, more complex & more expensive.


----
Stephen Kormilo      Email: .....Stephen_KormiloKILLspam.....UManitoba.Ca
Electronics Technology,  Red River Community College
Winnipeg, MB,  CANADA

>>(Do not ask me about details regarding this code, as I _not_ am the
>> author of this code - Kavli)
>
>    No kidding, Ronny... How about asking the authors of FIDE for
>    permission before you go posting their copyrighted code to the
>    world?  Or at least acknowledging the copyright?

Since Andrew Warren has forced me :-) to investigate in this, the
author of the code I supplied is Raymod Carr. I don't know if he was
employed by Aptronix at the time the code was written or if the code
was bought by Aptronix at a later date or whatever.

In any case Raymond should be acknowledged for writing that code.
Newer versions of the code can be found by anonymous ftp at:

ftp.gre.ac.uk:/pub/robotics/motorola/mcu11/

Regards,
-------------------------------------------------------------------------------
Ronny H. Kavli                      This message was composed by 10,000 monkeys
EraseMEkavlispam_OUTTakeThisOuTludd.luth.se                  keying on 10,000 computers.  It was then
Lulea Academic Computer Soc.(Ludd)  merged using COBOL.  This was of course
Lulea University, Sweden            all done under a government contract.

1995\11\09@043913 by Errington A

A range of 3wire displays are made by III-V systems, and stocked by Farnell
in the UK.  They include 2 digit and 4 digit 7seg displays in red and
green.

They are all based on the MM5450N display driver chip, which takes 34 serial
data bits in on the 3 wire interface and controls 34 LED segment drivers.

Andy
---------------------------------------------------------------------
Andrew M Errington                               Tel: +44 1524 593678
Microcomputer Consultant                         Fax: +44 1524 844011
Lancaster University                      a.erringtonspam_OUTlancaster.ac.uk
Lancaster LA1 4YW     www.lancs.ac.uk/people/cpaame/cpaame.htm
---------------------------------------------------------------------

>Does anyone know where I can purchase LT8522 led display referrenced in
>AN592? Is there a "better" device? I'm looking for any serial led display
>with at least 3 seven seg. displays and built in logic/latches for serial
>interface.  Thanks, Eric Seeley

1995\11\09@082624 by Warren Crossfield

Eric;

   Here's one used the other day...worked without any trouble at all!


   MAXIM MAX7219CWG-ND  (That's the Digi-Key part# for the SO-24 part)

   $8.27 ea.

   Serial input 8 digit LED Driver Multiplexed.


cheers.



                                           -Warren
_______________________________________________________________________________
Subject: 3 WIRE LED DISPLAY
From:    e_seeley%@spam@OWENS.RIDGECREST.CA.USKILLspamprdnet.polaroid.com at INET
Date:    11/8/95  9:45 PM

Does anyone know where I can purchase LT8522 led display referrenced in
AN592? Is there a "better" device? I'm looking for any serial led display
with at least 3 seven seg. displays and built in logic/latches for serial
interface.  Thanks, Eric Seeley

1995\11\10@122829 by Preben Granberg

'Re : 3 wire LED display (well 2 wire)'
1995\11\10@131535 by Robin Abbott

I suggest that an excellent device for 2 wire I/O expansion is the
M5450. This offers 34 output bits clocked in on a data and
clock line, the outputs only being transferred on the last
clock. It's perfect for up to 4, seven segment displays,
driven on a non-mux basis, good for other apps as well !

Robin

KILLspamrobin.abbottKILLspamdial.pipex.com

1995\11\10@140006 by reginald neale

1996\05\04@101935 by JACOB SCOTT

'mail failed, returning to sender'
1996\05\30@145934 by myke predko

Let's Try This Again...

|------------------------- Message log follows: -------------------------|
no valid recipients were found for this message
|------------------------- Failed addresses follow: ---------------------|
<RemoveMEpiclistTakeThisOuTmitvma.mit.educ> ... unknown host
|------------------------- Message text follows: ------------------------|
Received: from dial042.passport.ca by passport.ca with smtp
       (Smail3.1.28.1 #3) id m0uPBcn-001CRJC; Thu, 30 May 96 13:35 EDT
Message-Id: <spamBeGonem0uPBcn-001CRJCspamBeGonepassport.ca>
Date: Thu, 30 May 96 13:35 EDT
X-Sender: TakeThisOuTmykeEraseMEspam_OUTpassport.ca
X-Mailer: Windows Eudora Version 1.4.4
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
To: RemoveMEpiclistTakeThisOuTmitvma.mit.educ
From: mykeEraseME.....passport.ca (myke predko)
Subject: Microchip PIC Seminars


Hi Folks,

We just had our first PC Seminar here in the great white North (Toronto).
If you haven't signed up for a session yet, you should really do so.  Lots
of useful information and a good presentation on the PIC and some good
example applications.  The session is a (very) good tutorial for MPLAB.  I
learned a few things that I hadn't discovered on my own yet.

I recommend that you bring a bag to carry the books home in (a few of the
people from work had to bum laundry bags from the Hotel the seminar was in,
to carry the docs in public transportation).  Also, ask a lot of questions...

The Toronto session was the first in which the PICStart Plus' were
available.  I've opened up the box and looked inside, but that's about it.
I'll try it out tonight and let everybody know what I think.  So far, it
looks a lot better than my PICStart 1B.  You get a single '84 as a sample in
the package.

What really surprised me about the session was the number of people present.
I guess there was about 150 in the Toronto Session.

Myke
Myke

"We're Starfleet officers, weird is part of the job."

Capt. Catherine Janeway


Myke

"We're Starfleet officers, weird is part of the job."

Capt. Catherine Janeway

1996\06\06@005341 by Steve Hardy

{Quote hidden}

> From: Byron A Jeff <EraseMEbyronCC.GATECH.EDU>
>
> The design I hit upon after thinking a bit revolved around multiplexing
> the 6 LEDs utilizing a common pin on one side. Something like:
>
>  Port pin---+-[220ohm]--+---[LED]------  Port pin
>             |
>             +-[220ohm]--+---[LED]------- Port pin
>             |
>             +-[220ohm]--+---[LED]------- Port pin
>             |
>             +-[220ohm]--+---[LED]------- Port pin
>
> And so on. One led can be selected by tristating all but one port pin
> on the right side. The selected LED's color can be picked by twiddling
> with the left port pin and the one non-tristated port pin.
>
> The question that popped into my mind during this design discussion was
> the relevance of the position of the resistor. Does it matter if the resistor
> is on the anode or the cathode side of an LED. Is putting the resistor on
> the anode side simply a convention or is there some other reason that

justifies
> its placement. Should a bi-polar have resistance on both sides (I've done this
> in previous designs)?
>

It makes no electrical difference which side the R is on.  Two 2-pin
devices in series may be used in any order.

BTW, the above circuit can also drive any 2 LEDs to arbitrary polarity
so long as consistent brightness isn't a problem.  How about 3 or more?
Have to think about that...

Regards,
SJH
Canberra, Australia

1996\06\06@013039 by Onat Ahmet

       > I would suggest an easy remedy to this is to use a bipolar LED
       one of
       > the two-lead red/green types, available at Radio Shack or any
       mail-order
       > electronics house) connected as shown:
       >
       > Gnd----[220ohm]---+---[220ohm]----+5
       >                   |
       >                   +---[LED]------- Port pin
       >
       > that this can be a useful trick for driving more than one
       "independently-
       Hmmm, I was having a discussion about bipolar LED's driven by PIC
       pins in
       one of my classes I'm teaching this summer just this morning. The
       objective
       was to drive 6 bi-polar LEDS (2 pin) using as few PIC port pins as
       possible.
       Each LED should be able to show red,green,yellow, and off.

       The design I hit upon after thinking a bit revolved around
       multiplexing
       the 6 LEDs utilizing a common pin on one side. Something like:

        Port pin---+-[220ohm]--+---[LED]------  Port pin
                   |
                   +-[220ohm]--+---[LED]------- Port pin
                   |
                   +-[220ohm]--+---[LED]------- Port pin
                   |
                   +-[220ohm]--+---[LED]------- Port pin

       And so on. One led can be selected by tristating all but one port
       pin
       on the right side. The selected LED's color can be picked by
       twiddling
       with the left port pin and the one non-tristated port pin.

Actually, I think there is nothing new under the sun really ;)
If you know about LED sign boards, this is how they work! You
seem to have simplified it into a single line! (the initial
poster did it down to a single pixel!) I think it is a nice idea
though!

       The question that popped into my mind during this design discussion
       was the relevance of the position of the resistor. Does it matter if
       the resistor is on the anode or the cathode side of an LED.

       BAJ

Theoretically both are identical. You don't need to put a resistor
to both ends of a bipolar LED either. I do not know how this setup
works with high frequencies (well, we have seen radio beacons
recently), so I cannot comment on that... (Not that many people would
drive their LED's at these frequencies!)

Is there any "catch 22" to this?


| Ahmet ONAT  Kyoto Univ. Japan                                 |
| E-mail    : RemoveMEonatEraseMEEraseMEkuee.kyoto-u.ac.jp                           |
| WWW page  : http://turbine.kuee.kyoto-u.ac.jp/staff/onat.html |
|             My 6 leg walker, RC airplanes & more in home page |

1996\06\06@031027 by Keith Dowsett

>        the 6 LEDs utilizing a common pin on one side. Something like:
>
>         Port pin---+-[220ohm]--+---[LED]------  Port pin
>                    |
>                    +-[220ohm]--+---[LED]------- Port pin
>                    |
>                    +-[220ohm]--+---[LED]------- Port pin
>                    |
>                    +-[220ohm]--+---[LED]------- Port pin

Hi,

  the problem with this design arises when you want all four LEDs running.
If we allow for 10mA through each LED the common pin has to source and sink
40mA. According to the 16C5X data sheet in front of me the specification is
sink 25mA and source 20mA. In addition to which there are limits on total
currents for each port, and for the total device.

One way around this is to use the common pin to drive a pair of transistors
but that increases the part count and we are still faced with a 40mA per
port limitation. Perhaps someone has a better solution.

Keith.
==========================================================
Keith Dowsett         "Variables won't; constants aren't."

E-mail:      RemoveMEkdowsettspam_OUTKILLspamrpms.ac.uk
Phone:       0181-740-3162
Fax:         0181-743-3987

Snail mail:  MRC Clinical Sciences Centre, Cyclotron Unit.
                Hammersmith Hospital. London W12 0NN.

1996\06\06@084308 by Rick Miller

Byron!!
Byron A Jeff wrote:

It *DOES* make a difference where you put the resistor,
since programmers invariably make *mistakes*.  With only
one resistor, it would be possible to burn out the left-hand
port pin if you were to drive too many of the right-hand
pins to the opposite polarity *simultaneously*.  That's all.

If you're careful, *really* careful, not to do that, then
all is well with only one resistor.  It makes absolutely
no difference which side of the LED you put the resistor
on, unless you want to use the roughly 1.3 V drop for some
sort of measurement purposes.

Use one "file" to hold bits to be driven during the "RED"
cycle and another to hold bits to be driven during the
"GREEN" cycle.  Yellow gets a bit in both.  Then cycle
through both files, one bit at a time.  That way you
can be pretty certain you're not going to drive more than
one LED at a time.

How 'bout loading the flag file into the data output
latches and then rotating the TRIS file with one bit
cleared?  :-)  Now you know I'm going to have to build
this thing, just to see it run.

You might also wish to lower the value of the current-
limiting resistor to allow the full 20mA that the pins
can put through it.  Since you're only going to be driving
the LEDs for very small duty cycles (1/12 at most) you
certainly won't have to worry about burning them out.
--
Rick Miller
<RemoveMErdmillerTakeThisOuTspamexecpc.com>

1996\06\06@131538 by Reginald Neale

1996\06\06@135517 by Byron A Jeff

1996\06\06@212913 by Steve Hardy

{Quote hidden}

> From: Byron A Jeff <EraseMEbyronspamspamBeGoneCC.GATECH.EDU>
>
> > If we allow for 10mA through each LED the common pin has to source and sink
> > 40mA. According to the 16C5X data sheet in front of me the specification is
> > sink 25mA and source 20mA. In addition to which there are limits on total
> > currents for each port, and for the total device.
>
> I'd pull the full 20ma through the currently activated LED.. It's only one
> LED, not all 6 that turn on at once so there's no need to limit the current to
> 10 ma
> >
> > One way around this is to use the common pin to drive a pair of transistors
> > but that increases the part count and we are still faced with a 40mA per
> > port limitation. Perhaps someone has a better solution.
>
> Correct. If brightness is a real problem (and in this application it isn't)
> then each port pin would have to drive a transistor pair. But that raises
> the next question: Can a transistor pair be tri-stated? If so how would you
> do it?
>

A transistor buffer can be tristated using only one output port, providing
that the output leakage is insufficient to bias either transistor.  In the
case of leakage, beware that the following circuit divides the output
impedance by the transistor beta (approximately).

                  Vcc
                  /
          -------|NPN
         |        \
port -----|         +---- out
         |        /
         --------|PNP
                  \
                  GND

(Geez I hate ascii graphics).  The emitters are tied together.  The output
follows the state of the port (High, Low or hi-Z).  The only problem is that
to output is no longer that good old rail-to-rail CMOS swing.  Instead,
the output falls short of the supply by one Vbe. (about 0.6V).

The available current is the port current times the transistor beta; in
practise limited by the allowable transistor collector current - approx 500mA.

One question I have is whether the datasheet limitations for port current
may be exceeded if a reduced duty cycle is used.  E.g. for continuous
operation 25mA is OK, is 100mA OK for 25% duty cycle?  My guess is
probably not due to excessive voltage drop in the output drivers due to
FET channel resistance, however it would be interesting to experiment.

Regards,
SJH
Canberra, Australia

1996\06\07@104539 by Mark K Sullivan

1996\06\08@162506 by Dwayne Reid

1996\06\09@072743 by David Knell

[diagram snipped]

>Steve - if you add a 10K resistor from bases to emitters, leakage becomes
>MUCH less of a factor.

And, if the Vbe drop is a problem, you can swap the transistors over,
resulting in output swinging to the rails - Vce(sat) (typically 0.2-0.3V).

                    Vcc
                    /
           -------|PNP
           |        \
port -/\/\/ +        +---- out
           |        /
           --------|NPN
                    \
                    GND

This has a disadvantage that it can't be tristated & that both transistors
are turned on during switching, resulting in potentially large amounts
of current being drawn.

Rearranging like this:

                       Vcc
                 +--+-----
                 |  |
                 /  |
                 \  /
           --/\/\+-|PNP
           |        \
port -------+        +---- out
           |        /
           --/\/\+-|NPN
                 \  \
                 /  |
                 |  |  GND
                 +--+-----

with about a 5:1 ratio between the series resistors and the B-E
resistors ought to be OK for a 5V Vcc.  Your resistors need to
be large enough for the standing current drawn to be acceptable,
and small enough so that there's enough base drive to the transistors.

I guess that another worthwhile observation is that the PIC port
outputs cease to swing rail-rail as soon as you draw any current;
I think I remember measuring one at something like Vcc-0.4 V when
sourcing 4mA.  The original circuit adds a further 0.7V drop to this;
the one above should be generally oblivious to such things.

Dave
------------------------------------------------------------
David Knell
Tel: 01843 846558
Fax: 01843 846608
E-mail: RemoveMEdaveKILLspamdave-ltd.co.uk

1996\06\10@184335 by Dwayne Reid

1996\06\11@051224 by David Knell

'USART and LED dimming'
1996\06\28@091604 by Harrison Cooper

1996\06\28@100358 by Scott Newell

1996\06\28@113613 by Harrison Cooper

1996\06\28@122754 by Brian Read

1996\06\28@165256 by Reginald Neale

As part of a PIC-based flasher project, I'm looking for high-brightness LEDs
in the 5000-7000 mcd range. Digi-Key and Mouser have 1640-2000 mcd, and
Jameco has a 7000 mcd, but I'm looking for sources in addition to Jameco
(cheaper, better, etc.). Quantities of around 100, at the moment. Any thoughts?

Chris

   ======================================================================
         Christopher Zguris  -  czgurisSTOPspamspam_OUTinterport.net  -  Uhhh, Ear?
                 1991 Honda VFR (Red, with red accessories)
            AMA, HSTA, CRV, HRCA, IVFROC, ex-Big Apple Vegetarian

                       BEAR RESISTANT FOOD CONTAINERS
      Made of high impact ABS plastic with stainless steel latches. The
       container is entirely flush and cannot be opened unless the bear
                         has a coin or screwdriver.
                              - CAMPMOR catalog
   ======================================================================

1996\08\14@160818 by Todd Peterson

At 02:33 PM 8/14/96 -0400, you wrote:
>As part of a PIC-based flasher project, I'm looking for high-brightness LEDs
>in the 5000-7000 mcd range. Digi-Key and Mouser have 1640-2000 mcd, and
>Jameco has a 7000 mcd, but I'm looking for sources in addition to Jameco
>(cheaper, better, etc.). Quantities of around 100, at the moment. Any thoughts?

Check out Marktech International Corp., (518)786-6591
Sorry, I don't know if they have a web site yet.

Todd Peterson, Computer Engineer   (spamBeGonetpetersonSTOPspamEraseMEnetins.net)
E-LAB Digital Engineering, Inc.

1932 Hwy. 20
P.O. Box 246
Lawton, IA 51030-0246
(712) 944-5344

Visit us at: http://www.netins.net/showcase/elab

1996\08\14@160943 by Paul Mathews

Christopher Zguris wrote:
>
> As part of a PIC-based flasher project, I'm looking for high-brightness LEDs
> in the 5000-7000 mcd range. Digi-Key and Mouser have 1640-2000 mcd, and
> Jameco has a 7000 mcd, but I'm looking for sources in addition to Jameco
> (cheaper, better, etc.). Quantities of around 100, at the moment. Any
thoughts?
>
....


Currently, the very highest brightness red LEDs are made by Mitsubishi
Cable (800 262 6200), however, very good ones are offered by Marktech
(Toshiba, 518 786 6591), Sharp (800 642 0261), Siemens Opto (408 777
4968), Stanley (, and others.  Note that the brightness spec depends
strongly on coverage angle.  The easiest way to achieve a very high
brightness spec is to narrow the angle by means of a longer focal
length: brightness varies with the inverse square of coverage angle.
That's one reason why the jumbo packages achieve higher brightness: they
maintain low f# even with a longer FL.

Since you mention Digikey, I assume you're in USA, and the above are the
USA phone #s:


--

Paul Mathews, consulting engineer
AEngineering Co.
KILLspamoptoengspamBeGonewhidbey.com
non-contact sensing and optoelectronics specialists

1996\08\14@162225 by Mark K Sullivan

'PIC controlled freq generator'
1996\08\15@035248 by thoffman

1996\08\15@120151 by Rick Sherman

Tim Hoffman writes:
>
> OK, here's a good one:
>
> I need to control an oscillator so that I can generate a frequency in
> the range of 4-14MHz with a PIC. I'd really like to chop that range
> into 256 or 65536 different freqs that can be controlled by shifting a
> word into a shift register.
>
Take a look at the Fox F6053A it's a programmable ttl oscillator.
It can be programmed to work from 360khz to 120 Mhz. It's not cheap at
about $18-$20.



--
*==========================================================================*
* Rick Sherman                  * Virtual Computer Corporation
* EraseMErickEraseMEvcc.com                  * The Reconfigurable Computer Company.
* 818-342-8295                  *
*==========================================================================*

1996\08\15@144124 by Martin J. Maney

1996\08\15@153005 by Mike Riendeau

'Bright LEDs'
1996\08\15@182350 by Jon Bertrand

    People around here call me the LED junkie.

    Toshiba makes 18000mcd orange/red LEDs (20mA @ 2.4V) that will blow
    your eyeballs out of your head if you look at them.

    They are clear.  I don't recall what they cost.  Marktech sells them
    in the U.S.

    Toshiba also has a nice green LED at 8000 mcd - looks good  :)


    If you need the part numbers and phone numbers I can get them for you
    Monday.  Let me know.

    Jon Bertrand
    @spam@jonb@spam@spam_OUTcirris.com

'IR leds for remote ctrl'
1996\08\15@183441 by engmessi

Hello, friends.

I am trying to find a good IR led (and receiver, also) for remote control
purposes. I heard about the TIL38, with a switched current of 2A (10
microsecond pulses, 1 millisecond frame) or 100 mA continuous. I could not
find these here in Brazil, though.

I am sure some of you have already dealt with these components and know
other options, as well as a good receiver and some good tips.

Which makes the best detector, a phototransistor or an infrared sensor
(those mounted in a smoked case) ?

The application is a 'too close' sensor. I want to oscillate the led and PIC
the reflected beam, reflected by a 'clear' (skin color) surface. I want a
range around 8 to 10 inches. Do you think I will have to use extra lenses ?

Thanks,


Pedro.


______________________________________________________
Pedro Drummond
Engenharia Mestra de Sistemas / SP / Brasil
Voice: 55-11-883.4799   Fax: 55-11-883.4926
e-mail: spamBeGonemestraKILLspamu-netsys.com.br
______________________________________________________

1996\08\15@200214 by Steve Hardy

> From: Engenharia Mestra de Sistemas Sociedade Ltda
>               <.....mestraspam_OUTu-netsys.com.br>
>
> Hello, friends.
>
> I am trying to find a good IR led (and receiver, also) for remote control
> purposes. I heard about the TIL38, with a switched current of 2A (10
> microsecond pulses, 1 millisecond frame) or 100 mA continuous. I could not
> find these here in Brazil, though.
>
> I am sure some of you have already dealt with these components and know
> other options, as well as a good receiver and some good tips.
>
> Which makes the best detector, a phototransistor or an infrared sensor
> (those mounted in a smoked case) ?
>
> The application is a 'too close' sensor. I want to oscillate the led and PIC
> the reflected beam, reflected by a 'clear' (skin color) surface. I want a
> range around 8 to 10 inches. Do you think I will have to use extra lenses ?

For this application, there is no need to go to such lengths.  Unless
you want a high bandwidth for comms purposes, use a standard IR remote
control receiver module.  These are 3-pin devices which look a bit like
a TO-220 package without the heatsink.  They run off 5V and output a
TTL level signal.

Any IR LED can be used (preferably about 900nm wavelength).  This
should be modulated at 38-40KHz, in bursts lasting about 1ms.  If using
a PIC, this can be programmed to directly drive the LED (including the
40KHz modulation) as well as read the signal from the detector, where
it looks for a correlation.  Since you are only interested in a range
of 20-25cm, the LED can be driven directly from a PIC pin with a series
resistor.  I have used this approach many a time and it works a charm.
The detection threshhold is adjusted by varying the series resistor.

One thing I learnt early on is that the receiver, being very sensitive,
is susceptible to electrical interference.  Make sure it is well
shielded from the LED and other (relatively) high current PCB traces.
Use decoupling capacitors.  Make sure that the receiver is shielded
from direct line-of-sight to the LED.  The LED should be enclosed in an
opaque container with an aperture at the front.

The advantage of using an IR module is that it is much less susceptible
to ambient conditions (e.g. fluorescent lights) than rigging your own
using a photodiode.  The overall system cost should be lower.

Regards,
SJH
Canberra, Australia


PS:  The detector does not respond instantaneously to the IR signal.
In general, the delay is longer for a weaker signal.  By implementing
a timing function, it may be possible to estimate a range.  This would
help implement a bit of hysteresis if so desired.

1996\08\15@211954 by Paul Mathews

Engenharia Mestra de Sistemas Sociedade Ltda wrote:
{Quote hidden}

>
> Hello, friends.
>
> I am trying to find a good IR led (and receiver, also) for remote control
> purposes. I heard about the TIL38, with a switched current of 2A (10
> microsecond pulses, 1 millisecond frame) or 100 mA continuous. I could not
> find these here in Brazil, though.
>
> I am sure some of you have already dealt with these components and know
> other options, as well as a good receiver and some good tips.
>
> Which makes the best detector, a phototransistor or an infrared sensor
> (those mounted in a smoked case) ?
>
> The application is a 'too close' sensor. I want to oscillate the led and PIC
> the reflected beam, reflected by a 'clear' (skin color) surface. I want a
> range around 8 to 10 inches. Do you think I will have to use extra lenses ?
>
> Thanks,
>
> Pedro.
>
> ______________________________________________________
> Pedro Drummond
> Engenharia Mestra de Sistemas / SP / Brasil
> Voice: 55-11-883.4799   Fax: 55-11-883.4926
> e-mail: TakeThisOuTmestra.....TakeThisOuTu-netsys.com.br
> ______________________________________________________

One good source is Siemens:

T1-3/4 (5 mm bullet pkg) IR LEDs:
-------------------------------------------------------------
Hi power AlGaAs (880nm)         SFH484-2 and similar P/Ns
Hi power GaAs (940nm)           SFH415-U

The GaAs parts tend to have faster rise and falltimes.

Most IR LEDs will handle short pulses (microseconds) at currents up to
about 2 Amps provided that average current is within ratings.  Be
careful that your drive waveform never puts out long pulses, though.

For photodiodes, the world's most popular P/N is probably BPW34F, which
is an  IR filter 2 pin DIP.  For a lenses photodiode, consider the
SFH203 range, which has various suffixes depending on angular coverage
and filtering.

If you want to work with an integrated module, have a look at the
Hamamatsu S3599 or the Sharp IS471F.  These 4 pin devices require only
an external bypass capacitor, a resistor, and an LED to make a
modulated, EMI/RFI immune, sunlight immune sensor.  The unlensed
versions are quite cheap. To achieve your desired range, you can either
add a simple lens or boost the current drive to the LED with an external
transistor.

You can email me with further questions.
--

Paul Mathews, consulting engineer
AEngineering Co.
TakeThisOuToptoengKILLspamspamwhidbey.com
non-contact sensing and optoelectronics specialists

1996\08\15@215153 by EVAN CRANNA

1996\08\15@222809 by Paul Haas

On Thu, 15 Aug 1996, Engenharia Mestra de Sistemas Sociedade Ltda wrote:

> The application is a 'too close' sensor. I want to oscillate the led and PIC
> the reflected beam, reflected by a 'clear' (skin color) surface. I want a
> range around 8 to 10 inches. Do you think I will have to use extra lenses ?

I made something similar.  I used a PIC to modulate an IR LED at 40Khz and a
Sharp IR reciever (GPU(something)-X, sorry don't remember the part number).
It had a range of 6 inches with sunlight shining onto the wall, and 18 feet
with the blinds drawn.  It didn't work at all in my work room, because the
high efficiency lights are also high frequency lights.

If you control the lighting, then IR can work for you.  If the lighting isn't
under your control, use a different technology.  Under constant lighting
conditions, I could control the range by changing the current limiting
resistor.

--
Paul Haas
.....paulhRemoveMEhamjudo.com

1996\08\16@005256 by Paul Mathews

Paul Haas wrote:
> I used a PIC to modulate an IR LED at 40Khz and a
> Sharp IR reciever (GPU(something)-X, sorry don't remember the part number).
> It had a range of 6 inches with sunlight shining onto the wall, and 18 feet
> with the blinds drawn.  It didn't work at all in my work room, because the
> high efficiency lights are also high frequency lights.
>
> If you control the lighting, then IR can work for you.  If the lighting isn't
> under your control, use a different technology.

I must comment on this response to the original query.

First, TV remote control IR links are not designed to operate in strong
light.  Their designers make the reasonable assumptions that: a) people
don't usually watch TV in strong light, and b) if you don't manage to
get the device to work, you will refine your aim and try again.

So, don't be surprised that they don't work as well in strong light.

On the other hand, it's fairly easy to design an active IR sensor that
works fine in an arbitrary amount of ambient light.  I've designed
sensors that work well in 1 million lux of ambient, without any change
in range from total darkness, with white target ranges up to 40 metres.
The 'secrets' are: directional optics, low impedance photodiode loading,
bandpass preamplification, and effective modulation/demodulation
(generally NOT with the square waves used in IR controls).  Proper
synchronous demodulation techniques can easily determine signal
presence/absence in SNRs worse than -40db.  The Hamamatsu S3599 chip
mentioned earlier is simple and cheap, has a 300nW threshold, and shows
no range reduction at 80,000 lux.  The addition of a single lens reduces
its field of view, and raises its ambient light tolerance, while
increasing its sensitivity.

Finally, I take issue with what I perceive to be the nature of the
reply, which I'll paraphrase thusly:  I tried this and couldn't make it
work, so there's no use in your trying.  It seems to me that the best
new ideas come from people who don't know that they "can't".

--

Paul Mathews, consulting engineer
AEngineering Co.
RemoveMEoptoengspamBeGonewhidbey.com
non-contact sensing and optoelectronics specialists

1996\08\16@005920 by Steve Childress

Regarding...

If you want to work with an integrated module, have a look at the
Hamamatsu S3599 or the Sharp IS471F.  These 4 pin devices require only
an external bypass capacitor, a resistor, and an LED to make a
modulated, EMI/RFI immune, sunlight immune sensor.  The unlensed
versions are quite cheap. To achieve your desired range, you can either
add a simple lens or boost the current drive to the LED with an external
transistor.

You can email me with further questions.
--

Paul Mathews, consulting engineer
AEngineering Co.
spamBeGoneoptoeng@spam@spam_OUTwhidbey.com
non-contact sensing and optoelectronics specialists



I've not seen the "lensed" IR demodulatators - any pointers to a distributor?

1996\08\16@013510 by Paul Mathews

Steve Childress wrote:
{Quote hidden}

>
> Regarding...
>
> If you want to work with an integrated module, have a look at the
> Hamamatsu S3599 or the Sharp IS471F.  These 4 pin devices require only
> an external bypass capacitor, a resistor, and an LED to make a
> modulated, EMI/RFI immune, sunlight immune sensor.  The unlensed
> versions are quite cheap. To achieve your desired range, you can either
> add a simple lens or boost the current drive to the LED with an external
> transistor.
>
> You can email me with further questions.
> --
>
> Paul Mathews, consulting engineer
> AEngineering Co.
> TakeThisOuToptoengspamwhidbey.com
> non-contact sensing and optoelectronics specialists
>
> I've not seen the "lensed" IR demodulatators - any pointers to a distributor?

The P/N for the lenses metal can version is:  S4282-72

I've always dealt directly with Hamamatsu.
Hamamatsu USA phone 908 231 0960
They're on the WWW via IndustryNet, and they have an email address
listed there.
--

Paul Mathews, consulting engineer
AEngineering Co.
optoengEraseMEwhidbey.com
non-contact sensing and optoelectronics specialists

'PIC controlled freq generator'
1996\08\16@212203 by Mr. Brooke Clarke

Andres


>I'm working on a project that's quite long (about 10K lines of code)
>for a moving-message-LED-display controlled by a 16C73 that has a lot
>of features. It's working nicely and it's almost finished.

Hmm.... I found this quite interesting.  I also made a number of
moving message displays a couple of years ago based on the PIC16C57.
(On those days the fancier models like the 16C73 did not exist yet.)

Even though the moving message display worked very well and ran very
smoothly, at the end of that project I was sorry that I didn't rather
use a bigger micro like the 8051 or something that I could program in
a high level language like C.   The PIC16C57 that I used was filled
to the brim with code and there was no more room for future expansion
and that eventually killed the project as far as I was concerned.

But I suppose the 16C73 is a far better choice than the 16C57 and at
least you get some fancy C compilers for the PIC microcontrollers
these days.     Best of luck with your project!

Regards

Werner

--
Werner Terreblanche   Tel +27 21 7102251   Fax +27 21 721278
RemoveMEwterrebEraseMEspam_OUTplessey.co.za (work) OR @spam@wernerRemoveMEEraseMEaztec.co.za  (home)

1996\10\30@012333 by Andres Djordjalian

1996\10\31@040427 by Werner Terreblanche

Andres Djordjalian <EraseMEaajordj@spam@ALEPH.FI.UBA.AR> wrote:


>I also started this project using a 16C57, but it soon proved too
>small for what I had in mind. I could make it display text but it
>seemed almost impossible to add the other features that where needed.
>If you were able to complete a display controlled by a 16C57 I
>congratulate you!

Thank you.  I won't tell you how long it took me develop that. :(
I also had  to implement 9600 baud  serial communications all with
this one PIC1657.  And this was still in the dark ages before
Internet, so I didn't have any application notes or a Piclist to
consult.  <grin>

>I still can't say if it would had been better to use another micro.
>What I like of PICs is their small package and speed. I needed speed
>for what I had in mind, and I wanted to minimize costs and PCB
>complexity.

Well, you get the 8051 devices also in very high speed models.  I
know a guy here who makes gigantic big graphical LED displays, and he only
uses the fast 8051 devices.   So speed is not really a problem
anymore for these devices, but ROM considerations and development
tools and compilers certainly is.  If you feel that you are more
confident with the PIC microcontrollers then that is certainly the
right way to go.


>And also I guess the 4K-word ROM on the 16C73 is equivalent to almost
>10K bytes on another micro, and more if it's programmed with a HLL, so
>unless there is a 16K or 32K ROM microcontroller that is cheap and
>fast I think the 16C73 might be a good choice... But thanks for your
>comment!

The only problem is that they are all one time programmable.  (Except
for the PIC16C84, but that one is too small for your application.)   I really
like the
Atmel devices, because they are cheap, multi programmable and low on
power consumption.  However, that is just my personal opinion.  I
have gone through this same process once before and if I have to do
it all over again, I would rather use the Atmel 89CXX processors.

--
Werner Terreblanche   Tel +27 21 7102251   Fax +27 21 721278
@spam@wterrebspam_OUT.....plessey.co.za (work) OR spamBeGonewernerEraseMEaztec.co.za  (home)

1996\11\02@161937 by John Payson

1996\11\02@190333 by William Chops Westfield

'words vs. bytes (was Re: LED mvong message.)'
1996\11\02@201717 by Eric Smith

'LED mvong message.'
1996\11\02@203553 by fastfwd

William Chops Westfield <PICLISTspamBeGoneMITVMA.MIT.EDU> wrote:

> I have a hard time believing that any processor can fetch twice as
> many bytes in its instruction stream and maintain the same
> execution time...

What you're missing, Bill, is that it's very easy to go the OTHER
way... That is, to fetch HALF as many bytes in the same time.

Look at it from that perspective, and remember that the 8051 has an
internal divide-by-12 on its clock, and you'll see that all that's
happening is that the short instructions are executing much slower
than they absolutely have to.

-Andy

Andrew Warren - RemoveMEfastfwd@spam@spamBeGoneix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499

1996\11\03@114836 by Gerhard Fiedler

1996\11\03@114839 by Gerhard Fiedler

1996\11\03@164342 by John Payson

1996\11\03@210816 by Dwayne Reid

'words vs. bytes (was Re: LED mvong message.)'
1996\11\05@152505 by Matthew Mucker

1996\11\05@205802 by Martin J. Maney

1996\11\05@211035 by Eric Smith

"Martin J. Maney" <.....maney@spam@EraseMEMCS.NET> wrote:
> I can't resist mentioning that I have a 6501 lurking in a dusty drawer.

I've got a 6501.  And a 6502 that is early enough that it doesn't have the
ROR instruction, which was added in September of 1975.

But I've rewritten most of the embedded system code I originally wrote for the
6502 and the Mitsubishi 8-bit parts (6502-like) to run on the PIC.

Cheers,
Eric

1996\11\06@112231 by myke predko

'LED matrix multiplexing'
1996\11\10@174111 by Zhahai Stewart

I am considering building a small LED matrix sign, probably
using 12 stackable 8x8 LED matrix blocks (approx 2"x2").  This
would produce a display surface of 8 rows each 96 wide - enough
for 16 chars of 5x8 with one space between.  (One use would be
a Caller ID I could read at night with my glasses off :-)

How is this generally done?  If I did 8 way multiplexing, with
20 ma current per LED, this would mean about 2 amps draw.  This
could be done with 96 high side drivers sourcing 20 ma each,
96 current limiting resisters, and 8 low side drivers sinking
about 2 amps each (fairly hefty).  Or reverse this, and have 96
low side drivers (at this current, could be PICs directly) and
8 x 2 amp high side drivers.  OR I could split up the common side,
into, say, 3 groups of 4 matrix blocks, each with it's own driver
(to keep the current in the shared driver down) - but this would mean
24 common side drivers (plus 96 on the other side).  Is there a
preferred architecture?

Questions:

Is 1/8 duty cycle enough?

That would mean an average of 2.5 ma current for each lit
LED, which seems rather small; would I need higher current?
(50 ma/LED means 5 amp drivers!).

Is there a prefered direction for scanning, like top row to
bottom row (vs side to side within each 8x8 block)?

Other suggestions?
  Thanks, Zhahai


@ Zhahai Stewart       .....zhahaiRemoveMEhisys.com
@ A Meme Gardener      http://rainbow.rmii.com/~hisys/zhahai.html
@ Standard Disclaimer  YMMV - Your Maya May Vary

1996\11\10@200207 by Byron A Jeff

>
> I am considering building a small LED matrix sign, probably
> using 12 stackable 8x8 LED matrix blocks (approx 2"x2").

I thought the whole display was 2x2 (i.e. small) but i realize that
is would be 8x96 and 2 feet long...

> This
> would produce a display surface of 8 rows each 96 wide - enough
> for 16 chars of 5x8 with one space between.  (One use would be
> a Caller ID I could read at night with my glasses off :-)

I want a nice lit display for a security panel. Unfortunately it's
a bit too big for my tastes. I'm looking for something like 5 5x7
elements that fit on a 14 pin DIP...

>
> How is this generally done?  If I did 8 way multiplexing, with
> 20 ma current per LED, this would mean about 2 amps draw.

Which is absolutely too much...

>  This
> could be done with 96 high side drivers sourcing 20 ma each,
> 96 current limiting resisters, and 8 low side drivers sinking
> about 2 amps each (fairly hefty).  Or reverse this, and have 96
> low side drivers (at this current, could be PICs directly) and
> 8 x 2 amp high side drivers.

Wait I'm missing something. Aren't these displays internally multiplexed?
Something along the lines of having 16 pins with all the anodes of a row
connected together and all the cathods of a column? It would neve occur
to me to try to drive all 96 bits at the same time. Think one column at
a time.



>OR I could split up the common side,
> into, say, 3 groups of 4 matrix blocks, each with it's own driver
> (to keep the current in the shared driver down) - but this would mean
> 24 common side drivers (plus 96 on the other side).  Is there a
> preferred architecture?

How I've done it lately is to light one column at a time. I usually
use a 7445 BCD to 1-10 decoder because each pin can drive 80 ma (which
would be 10ma per led. Then all you'd need is one 8x10ma driver for
all the columns and one 7445 for each 10 columns (i.e. 10 for your application)
Another possibility is to use something like the Allegro Semi drivers
which can suck up a 1/2 A per line as long as only one line is on...


>
> Questions:
>
> Is 1/8 duty cycle enough?

Certainly. A typical PIC could drive this display in the 100's of kHz range.
That's why I'm suggesting 1/96 duty cycle. You can really
>
> That would mean an average of 2.5 ma current for each lit
> LED, which seems rather small; would I need higher current?
> (50 ma/LED means 5 amp drivers!).

Consider how long it's going to take you to set up 96 lines I'd go for
the much smaller duty cycle at much higher current.

>
> Is there a prefered direction for scanning, like top row to
> bottom row (vs side to side within each 8x8 block)?

Doesn't matter as long as it's fast enough. Typically I do one column
at a time from left to right.
>
> Other suggestions?

Yup. Up the current, drop the duty cycle. Remember you'll need at a minimum
96 bytes of memory, so it'll limit the choice of pics you can use.

>    Thanks, Zhahai
>
>
> @ Zhahai Stewart       .....zhahaiSTOPspam@spam@hisys.com
> @ A Meme Gardener      http://rainbow.rmii.com/~hisys/zhahai.html
> @ Standard Disclaimer  YMMV - Your Maya May Vary
>

1996\11\10@210411 by Bob Blick

1996\11\11@015403 by Werner Terreblanche

>I am considering building a small LED matrix sign, probably
>using 12 stackable 8x8 LED matrix blocks (approx 2"x2").  This
>would produce a display surface of 8 rows each 96 wide - enough
>for 16 chars of 5x8 with one space between.  (One use would be
>a Caller ID I could read at night with my glasses off :-)

>How is this generally done?  If I did 8 way multiplexing, with
>20 ma current per LED, this would mean about 2 amps draw.  This
>could be done with 96 high side drivers sourcing 20 ma each,
>96 current limiting resisters, and 8 low side drivers sinking
>about 2 amps each (fairly hefty).  Or reverse this, and have 96
>low side drivers (at this current, could be PICs directly) and
>8 x 2 amp high side drivers.  OR I could split up the common side,
>into, say, 3 groups of 4 matrix blocks, each with it's own driver (to
>keep the current in the shared driver down) - but this would mean 24
>common side drivers (plus 96 on the other side).  Is there a preferred
>architecture?

Zhahai

 I used to make LED displays like the one you describe.  Mine worked
as follows:

I used a row of 74HC164 shift registers, all connected in series so
that whatever you clock in at the first one, would eventually get to the
last one.  Then every shift register was buffered by a ULN2803
driver.   If your display is 96 leds wide, then you will need 12 x
74HC164's and 12 x ULN2803's.   There will also be 96 resistors to
limit the current to the LED's.

The eight rows of  96 LEDS are switched on as a whole row, by means
of one of eight TIP31 transistors.   My duty cycle for each row was
about  2mS per row.


>Is 1/8 duty cycle enough?

Depends on the birghtness that you need from your display.  Use only
good bright LED's, and it should not be a problem.

>Is there a prefered direction for scanning, like top row to
>bottom row (vs side to side within each 8x8 block)?

I found that my direction of scanning caused a slant of the font in a
particular direction.  I rather liked a forward slant in it.

Please feel free to ask any more question.  If you want, I can even
provide you with some of my old display boards to do your prototyping
on, but you will have to do the microprocessor part yourself.

Rgds
Werner



--
Werner Terreblanche   Tel +27 21 7102251   Fax +27 21 721278
wterrebEraseME@spam@plessey.co.za (work) OR RemoveMEwernerspamBeGoneaztec.co.za  (home)

1996\11\11@025942 by Eric Smith

Werner Terreblanche <spamBeGonewterrebKILLspam@spam@PLESSEY.CO.ZA> wrote:
>   I used to make LED displays like the one you describe.  Mine worked
> as follows:
>
> I used a row of 74HC164 shift registers, all connected in series so
> that whatever you clock in at the first one, would eventually get to the
> last one.  Then every shift register was buffered by a ULN2803
> driver.   If your display is 96 leds wide, then you will need 12 x
> 74HC164's and 12 x ULN2803's.   There will also be 96 resistors to
> limit the current to the LED's.

Note that Allegro (formerly Sprague) and other vendors of analog driver chips
such as the ULN2803 also make driver chips with integral shift registers.  I
don't have any part numbers handy, but I've used them in the past.  They
reduce package count, but I'm not sure whether or how much they reduce the
parts cost.

Cheers,
Eric

1996\11\11@111311 by Reginald Neale

>Werner Terreblanche <wterrebspam_OUT@spam@PLESSEY.CO.ZA> wrote:
>>   I used to make LED displays like the one you describe.  Mine worked
>> as follows:
>>
>> I used a row of 74HC164 shift registers, all connected in series so
>> that whatever you clock in at the first one, would eventually get to the
>> last one.  Then every shift register was buffered by a ULN2803
>> driver.   If your display is 96 leds wide, then you will need 12 x
>> 74HC164's and 12 x ULN2803's.   There will also be 96 resistors to
>> limit the current to the LED's.
>

Eric Smith said:
>Note that Allegro (formerly Sprague) and other vendors of analog driver chips
>such as the ULN2803 also make driver chips with integral shift registers.  I
>don't have any part numbers handy, but I've used them in the past.  They
>reduce package count, but I'm not sure whether or how much they reduce the
>parts cost.
>
They can. The Allegro 5810 thru 5818 are serial drivers from 10 to 32 bits.
They can be cascaded. All outputs can simultaneously sink 25 ma and still
stay within total package dissipation limits. On the design where I used it
a year or so ago, the 5812 (20 bits) was USD $2.58 in qty 100.


.....................Reg Neale.....................
Complete text of the winning entry in a recent good-government essay contest:
"Good Government.  Gooooood Government.   Sit.    Stay."

1996\11\11@111523 by Matthew Mucker

1996\11\11@112143 by Byron A Jeff

1996\11\11@122722 by hjmuller

> Date:    Sun, 10 Nov 1996 16:35:27 -600
> From:    Zhahai Stewart <spamBeGonezhahai@spam@HISYS.COM>
> Subject: LED matrix multiplexing
>
> I am considering building a small LED matrix sign, probably
> using 12 stackable 8x8 LED matrix blocks (approx 2"x2").  This
> would produce a display surface of 8 rows each 96 wide - enough
> for 16 chars of 5x8 with one space between.  (One use would be
> a Caller ID I could read at night with my glasses off :-)
>
[part of message supressed]
{Quote hidden}

>
> Questions:
>
> Is 1/8 duty cycle enough?
>
> That would mean an average of 2.5 ma current for each lit
> LED, which seems rather small; would I need higher current?
> (50 ma/LED means 5 amp drivers!).
>
> Is there a prefered direction for scanning, like top row to
> bottom row (vs side to side within each 8x8 block)?
>
> Other suggestions?
>    Thanks, Zhahai
>
>
> @ Zhahai Stewart       RemoveMEzhahaiEraseMEKILLspamhisys.com
> @ A Meme Gardener      http://rainbow.rmii.com/~hisys/zhahai.html
> @ Standard Disclaimer  YMMV - Your Maya May Vary
>

Hi Stewart:
                I suggest that you use the MAX7129  DIP24 (from MAXIM). This is
a
SERIALLY INTERFACED, 8-DIGIT LED DISPLAY DRIVER and you can get a free sample
from WWW.MAXIM-IC.COM or PHONE 1-800-998-8800.
               Do you have any information about CALL ID system that you
mention ? I'm interested in this class of information, and other user on the
list too. (Have you Technical Specifications about CALL-ID?
               Bye, Hugo




-------------------------------
Hugo J. Muller
E-mail:    spamBeGonehjmullerspam_OUTRemoveMEsatlink.com
Parana - Entre Rios - Argentina
-------------------------------

1996\11\11@165348 by Dwayne Reid

'LED matrix multiplexing (Correction !!!)'
1996\11\11@235223 by hjmuller

[Supressed message)
Hi Stewart:
                I suggest that you use the MAX7219  DIP24 (from MAXIM). This is
a
SERIALLY INTERFACED, 8-DIGIT LED DISPLAY DRIVER and you can get a free sample
from WWW.MAXIM-IC.COM or PHONE 1-800-998-8800.
               Do you have any information about CALL ID system that you
mention ? I'm interested in this class of information, and other user on the
list too. (Have you Technical Specifications about CALL-ID?
               Bye, Hugo

Sorry, in the previous message i write MAX7129 while the correct part number
is MAX7219. Thanks to Matt.


-------------------------------
Hugo J. Muller
E-mail:    .....hjmullerRemoveMEsatlink.com
Parana - Entre Rios - Argentina
-------------------------------

1996\11\12@025049 by fastfwd

I forget who started this thread, but here's a bit of advice...

Many people have suggested that the easiest/best way to multiplex all
those LEDs is with very high currents and very low duty cycles.

That's fine for the finished product, since each LED will only be
subjected to those very high currents for a short time.

While you're debugging your software, however, you should limit the
LED current to whatever value your LEDs can handle CONTINUOUSLY.  If
you're single-stepping your code through an emulator (or if there's a
bug in your code that prevents the multiplexing from working
properly), this'll keep you from burning out hundreds of LEDs.

-Andy

Andrew Warren - fastfwd@spam@ix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499

1996\11\12@104136 by Zhahai Stewart

> > I am considering building a small LED matrix sign, probably
> > using 12 stackable 8x8 LED matrix blocks (approx 2"x2").

> >  This
> > could be done with 96 high side drivers sourcing 20 ma each,
> > 96 current limiting resisters, and 8 low side drivers sinking
> > about 2 amps each (fairly hefty).  Or reverse this, and have 96
> > low side drivers (at this current, could be PICs directly) and 8 x
> > 2 amp high side drivers.
>
> Wait I'm missing something. Aren't these displays internally
> multiplexed?

No, I believe that the 64 LED's in each of the twelve blocks are
arranged in an 8x8 matrix.  16 pins.  8 are cathodes for columns,
8 are anodes for rows (also available vice versa).  To me
the obvious way to scan them is to power one anode (of 8) at a
time, while driving the appropriate subset of cathodes (depending
one which LEDs in this row should be lit currently).

For 96 wide by 8 high (27" x 2", twelve x8x blocks), this means 96
individually controlled column drivers, and 8 massive row drivers.

There have been some great leads regarding low side drivers (for the
96 sinks).  What about the 8 high side (in this regard) high current
drivers, many amps each?  I now read that the peak current for some
of these LED blocks (per LED, 1/10 or less duty cycle) can be 80-100
ma!  (by 8, would be 640-800 ma per block, via the row anode, times
twelve is up to 10 amps!).  I don't have to have absolute maximum
brightness, so I could compromise this to much less current.  But it
seems that I still need 8 high current transistors for the
rows/anodes.

I have read that logic gate power MOSFETs when used high side
(between power and the LED anodes) take several volts (eg: 5)
above the power supply to switch!  That makes it hard to simply
interface them (as high side drivers) to PIC outputs.

How would I use a PIC output to switch approx 5 volts at 2-10 A
(most to least compromise) into each of the 8 anode/rows?  Only
one (or none) at a time is needed.  At LED multiplexing speeds;
no relays please :-)

I guess this also brings up the question of appropriate multiplexing
speeds.  Would a 16 msec cycle, with 2 msec per row, be a good
frequency?  Or does it need to be faster to avoid visible flicker?

Thanks for the help!
   Zhahai


@ Zhahai Stewart       EraseMEzhahaiRemoveMESTOPspamhisys.com
@ A Meme Gardener      http://rainbow.rmii.com/~hisys/zhahai.html
@ Standard Disclaimer  YMMV - Your Maya May Vary

1996\11\12@111426 by Byron A Jeff

1996\11\12@130644 by Bob Blick

1996\11\12@152027 by Zhahai Stewart

> Do you have any information about CALL ID system that you
> mention ? I'm interested in this class of information, and other
> user on the list too. (Have you Technical Specifications about
> CALL-ID?

No, I'm afraid I don't.  That was a later question :-)

If nothing else, I was thinking of starting from the Weeder Tech
caller ID PIC project.  Weeder Tech is at 513-752-0279.  Terry
Weeder writes up projects for Nuts-n-Volts magazine, as well as
selling interesting PIC based kits. (Caller ID, DTMF, X-10, IR..)

  Zhahai

@ Zhahai Stewart       RemoveMEzhahaiKILLspamTakeThisOuThisys.com
@ A Meme Gardener      http://rainbow.rmii.com/~hisys/zhahai.html
@ Standard Disclaimer  YMMV - Your Maya May Vary

1996\11\12@152033 by Zhahai Stewart

>>>> I am considering building a small LED matrix sign, probably
>>>> using 12 stackable 8x8 LED matrix blocks (approx 2"x2").
>>>>
>>>> This could be done with 96 high side drivers sourcing 20 ma each,
>>>> 96 current limiting resisters, and 8 low side drivers sinking
>>>> about 2 amps each (fairly hefty).

>> [These are interally multiplexed]

>> No, I believe that the 64 LED's in each of the twelve blocks are
>> arranged in an 8x8 matrix.  16 pins.  8 are cathodes for columns,
>> 8 are anodes for rows

> What you just described is internally multiplexed.

OK.  Just not the way I use the term, no problem.

> You're still thinking in terms of driving an entire 96 element row.
> It's not necessary I believe but of course the biggest display I've
> built only had 40 columns. I drove one column at a time (max 7 LED
> on at a time using 5x7 displays). Looked great.

I am concerned that I could not get much brightness from a 1/96 duty
cycle.  Two modules I've looked at are spec'd at:

 max  80ma@1/16 or 15ma continuous (surplus)
 max 100ma@1/10 or 20ma continuous (new)

I'm not sure how much I can boost the max current with a low duty
cycle; I am assuming that there is a max dissipation limit (long
term as well as short term) as well as possibly other limits.
Suppose I boosted the former (surplus) module to 100 ma.  That would
be barely over 1 ma average current (at 1/96 duty cycle,
multiplexing).

Anybody else have any experience with such a stretched out
multiplexing cycle?  I presume it would work (at the 48 KHz
pulse/500 HZ cycle you suggest to avoid flicker), but be
fairly dim.  I have in mind using the display for multiple
purposes, some outdoors (tho not in direct sunlight).

You are right that it would simplify the electronics in some
ways.

But this would mean driving 8 LED's at time, with 100 ma
current each, so each of the 96 column drivers would have to
sink 800 ma (when all LEDs in that column were lit).  The row
drivers would only have to source 100 ma each, not a biggie.
With 1/96 multiplexing, I couldn't drop these currents much and
still be visible at all!  (Say to 160 ma/colum, 20 ma peak per
LED, at 1/96 duty cycle).

I'm still leaning more towards 96 column drivers each sinking up
to 100 ma (eg: the TPIC6B595 suggested), and 8 mongo high side
drivers handling one row each for all 12 blocks; or 16 each driving
6 blocks (48 LEDs each); or 24 each driving 4 blocks (32 LEDs each),
etc.  I am still open to alternatives, tho.

> Also consider how long it going to take the PIC to load up 96 bits
> of data for each row.

They need to load it only 8x full cycle frequency.  If the shift
registers were clocked.  I am figuring around 5 PIC instructions
per bit to test a data bit, set the data out line, and pulse the
clock out line (40 instructions inline for one byte), plus say 8
per byte to load each byte in to be tested or shifted, for an
average of about 6 instructions per bit - if it were bit banged.
Could do better with a SSP if available.  To load a 96 bit shift
register (for the columns) this would be around 600 instructions
per LED row, times 8 is 5000 instructions per full refresh (to
load the shift register).  For a 500 Hz full refresh, this would
require a faster PIC; for less, less so.

The alternative of loading one 8 bit row driver shift register 96
times per cycle rather than one 96 bit column driver 8 times per
cycle, comes out to about the same.

Loading either 8 bits parallel would cut the time a great deal, if
there are enough spare I/O pins.  (In the 1/8 cycle scheme, I could
use 12 edge triggered latches in a sequence, and clock out 8 bits
at a time).

Thanks for all the helpful discussion!
   Zhahai

@ Zhahai Stewart       spamBeGonezhahai@spam@hisys.com
@ A Meme Gardener      http://rainbow.rmii.com/~hisys/zhahai.html
@ Standard Disclaimer  YMMV - Your Maya May Vary

1996\11\12@154332 by Clyde Smith-Stubbs

Zhahai Stewart <RemoveMEzhahaispam_OUTHISYS.COM> wrote:

> Anybody else have any experience with such a stretched out
> multiplexing cycle?  I presume it would work (at the 48 KHz
> pulse/500 HZ cycle you suggest to avoid flicker), but be
> fairly dim.

The human eye is more sensitive to peak brightness levels than
it is to average levels; in my experience a 1/10 duty cycle
looks about half as bright as a 1/1 duty cycle at the same
peak current. 1/96 is certainly low, but it might be worth
experimenting with. It's necessarily a subjective assessment.

It would be unwise to drive the display
at higher than rated peak current, though. And remember Andy's
warning about current limiting during development.


--
Clyde Smith-Stubbs       | HI-TECH Software,       | Voice: +61 7 3354 2411
clydespamhitech.com.au      | P.O. Box 103, Alderley, | Fax:   +61 7 3354 2422
http://www.hitech.com.au | QLD, 4051, AUSTRALIA.   |
---------------------------------------------------------------------------
For info on the World's best C cross compilers for embedded systems, point
your WWW browser at http://www.hitech.com.au, or email spam_OUTinfospam_OUTspam_OUThitech.com.au

1996\11\12@193632 by Dave Mullenix

1996\11\12@194101 by Gonzalo Palarea

1996\11\12@195056 by William Chops Westfield

1996\11\12@202632 by Byron A Jeff

This is an extremely interesting discussion....

>
> >>>> I am considering building a small LED matrix sign, probably
> >>>> using 12 stackable 8x8 LED matrix blocks (approx 2"x2").
> >>>>
> > You're still thinking in terms of driving an entire 96 element row.
> > It's not necessary I believe but of course the biggest display I've
> > built only had 40 columns. I drove one column at a time (max 7 LED
> > on at a time using 5x7 displays). Looked great.
>
> I am concerned that I could not get much brightness from a 1/96 duty
> cycle.  Two modules I've looked at are spec'd at:
>
>   max  80ma@1/16 or 15ma continuous (surplus)
>   max 100ma@1/10 or 20ma continuous (new)

So in fact they could be pulsed higher at a lower duty cycle. But like you said
let's take the 100ma.
>
> I'm not sure how much I can boost the max current with a low duty
> cycle; I am assuming that there is a max dissipation limit (long
> term as well as short term) as well as possibly other limits.
> Suppose I boosted the former (surplus) module to 100 ma.  That would
> be barely over 1 ma average current (at 1/96 duty cycle,
> multiplexing).
>

Well the eye doesn't work linearly. The pulsed brightness seems brighter
than the average. So an led pulsed at 100ma and 1/100 cycle will seem
much much brighter than the same led continous at 1ma.

> Anybody else have any experience with such a stretched out
> multiplexing cycle?  I presume it would work (at the 48 KHz
> pulse/500 HZ cycle you suggest to avoid flicker), but be
> fairly dim.  I have in mind using the display for multiple
> purposes, some outdoors (tho not in direct sunlight).

I haven't dealt with outdoor situations but like I said earlier I've built
a 40 column display pulsed at 1/40 duty cycle at 11ma each. plenty bright.

{Quote hidden}

>
> You are right that it would simplify the electronics in some
> ways.
>
> But this would mean driving 8 LED's at time, with 100 ma
> current each, so each of the 96 column drivers would have to
> sink 800 ma (when all LEDs in that column were lit).  The row
> drivers would only have to source 100 ma each, not a biggie.
> With 1/96 multiplexing, I couldn't drop these currents much and
> still be visible at all!  (Say to 160 ma/colum, 20 ma peak per
> LED, at 1/96 duty cycle).

That's your target. The TPIC6B595 can handle it and sourcing 20ma is no
problem. Keep adding columns until you don't feel it's bright enough, then
stop and add another set of anode drivers.

>
> I'm still leaning more towards 96 column drivers each sinking up
> to 100 ma (eg: the TPIC6B595 suggested), and 8 mongo high side
> drivers handling one row each for all 12 blocks; or 16 each driving
> 6 blocks (48 LEDs each); or 24 each driving 4 blocks (32 LEDs each),
> etc.  I am still open to alternatives, tho.

Try the pulsed low to medium current solutions first. BTW using the system above
how exactly are you going to control brightness? If you current limit the
high side drivers, then you'll get variable brightness. If you current limit
the columns, you'll need 96 resistors (i.e. a 16 pin pack for each display).
By dropping the current using 1 column, you only need 8 resistors for the
whole display, and the brightness will be constant.


{Quote hidden}

>
> > Also consider how long it going to take the PIC to load up 96 bits
> > of data for each row.
>
> They need to load it only 8x full cycle frequency.  If the shift
> registers were clocked.  I am figuring around 5 PIC instructions
> per bit to test a data bit, set the data out line, and pulse the
> clock out line (40 instructions inline for one byte), plus say 8
> per byte to load each byte in to be tested or shifted, for an
> average of about 6 instructions per bit - if it were bit banged.
> Could do better with a SSP if available.  To load a 96 bit shift
> register (for the columns) this would be around 600 instructions
> per LED row, times 8 is 5000 instructions per full refresh (to
> load the shift register).  For a 500 Hz full refresh, this would
> require a faster PIC; for less, less so.

OK now mine. Presume that port B is driving the anode drivers and Port A
the cathode serial drivers. On initialization the serial cathode string is
initialized by setting all drivers to 1. After that a single 0 is clocked
and latched into the drivers selecting successive columns. 6 instructions.
Now to prevent bleed from one column to the next the row drivers have to
be turned off between successive columns. So Port B has to be cleared, The
column switched, and portB loaded with the next value. Presuming that
indirect access is used to get the data for each column, we're talking
about 10/11 instructions total:

disploop clrf  portb
        bsf   porta,clock
        nop
        bcf   porta,clock
        nop
        bsf   porta,latch
        nop
        bcf   porta,latch
        movf  INDF,W
        movwf portb
        incf  FSR,F
        decfsz count,F
        goto  disploop

To get 500Hz per column a 2.688 Mhz clock is required. Probably a bit
faster because a small delay between columns is required.

>
> The alternative of loading one 8 bit row driver shift register 96
> times per cycle rather than one 96 bit column driver 8 times per
> cycle, comes out to about the same.

I guess I wasn't playing fair because I planned to load the short side in
parallel, and not bother to latch it (unless of course you need port B
for some other activity.)

BTW the senario above leaves 3 portA pins available on an 18 pin PIC for
communication.

>
> Loading either 8 bits parallel would cut the time a great deal, if
> there are enough spare I/O pins.  (In the 1/8 cycle scheme, I could
> use 12 edge triggered latches in a sequence, and clock out 8 bits
> at a time).

Could do that. I kind of like the cathode shift registers because no real
data is involved, just clocking and latching a bit that only changes at
the beginning of a cycle.
>
> Thanks for all the helpful discussion!
>     Zhahai
>
> @ Zhahai Stewart       zhahaispam_OUThisys.com
> @ A Meme Gardener      http://rainbow.rmii.com/~hisys/zhahai.html
> @ Standard Disclaimer  YMMV - Your Maya May Vary
>

'LED matrix multiplexing (Correction !!!)CNID'
1996\11\12@204055 by Lauw Lim Un Tung

hi,

It's better if you build your project with MC145447 (CNID IC) and display
the result to small LCD 16x2 than you make scanning display with LED
Matrix, because it has more difficulties.

_______________________________

       Lauw Lim Un Tung
       Pecindilan 5/14
       Surabaya 60273
         INDONESIA
phone  : 62-31-318895
e-mail : RemoveMEtungKILLspam@spam@peter.petra.ac.id
_______________________________

On Tue, 12 Nov 1996, William Chops Westfield wrote:

>     Here in North America, caller ID information is sent as standard 1200 baud
>     ASCII text between the first and second ring.  The signals are exactly
like
>     the ones used by your 1200 baud modem.
>
> Bell 202 or Bell 212?  (we'll assume it isn't Vadic 1200)
>
> I haven't used a 1200bps modem in about 15 years.  Can you even put a modern
> modem (ie, the 2400bps ones you can get for $10 surplus?) into a dedicated
> 1200bps mode where it won't need to train/etc before receiving digits?
>
> BillW
>

1996\11\12@211656 by Ian Stirling

1996\11\12@224814 by Dave Mullenix

1996\11\12@230931 by Byron A Jeff

'Caller ID modulation (was Re: LED matrix multiplex'
1996\11\12@230941 by Eric Smith

Dave Mullenix <djmullenspamBeGone.....FACSTAFF.WISC.EDU> wrote:

> Here in North America, caller ID information is sent as standard 1200 baud
> ASCII text between the first and second ring.  The signals are exactly like
> the ones used by your 1200 baud modem.

Yes, except that most people don't have a 1200 baud modem.  In the early
1980s, people commonly used Bell 212 modems that operated at 1200 bps, using
600 baud phase shift keying (PSK).

Caller ID uses Bell 202 compatible signalling, which is true 1200 baud
frequency shift keying (FSK), but only half duplex.  However, FSK is ideal
for rapid transfer of small amounts of data, as it does not require any
training sequence.  (That's also why credit card validation systems use
FSK.)  However, Bell 202 was never popular for use with personal computers.

Many currently produced modems support Bell 212, but very few support
Bell 202 for general use.

Modern modems use quadrature amplitude modulation (QAM):

       standard        data rate       buad rate
                       (bps)

       V.22bis         2400            600
       V.32            9600            2400
       V.32bis         14400           2400
       V.34            up to 28800     various, up to about 2700 IIRC
       V.34bis         up to 33600     various

The easiest way to receive caller ID signals is with a chip specifically
designed for that purpose, such as the Motorola MC145447.

Cheers,
Eric

'LED matrix multiplexing'
1996\11\13@053254 by Kalle Pihlajasaari

Hi all LED matrix fans,

A few comments.

Large Backlit LCD displays are available and might be suitable
in some circumstances.

To minimise the number of drivers required you should reorganise
your matrix into as close to a square as possible electrically.

For 8 x 96 you have 768 LEDs (sqrt = 27.7...) 'nice' numbers
are 24 x 32 which would give you a 1:24 multiplex with 32
collumns.  This will be a total of 56 drivers as opposed
to the 104 with the skinny display layout.  About half the number.

The multiplex time and max current are altered by about 3 (better
or worse depending on which way you were planning to drive the
skinny arrangement)

Now the problems are:

No longer quite as logical display arrangement
Possibly more high current drivers.
Slightly more code.

Cheers
--
Kalle Pihlajasaari     KILLspamkalle.....data.co.za
Interface Products     Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750      Fax: +27 (11) 402-7751

1996\11\13@085847 by Byron A Jeff

1996\11\13@093609 by Ray Gardiner

Brilliant flash!(pun)...this is easy, all you need to do is use
the new 8 pin pics use one for every column of leds if need be and then
simply drive each one from a clocked serial bus. let's say each
column is 8 leds, and then any width, The central controller
simple clocks the bit patterns to each 12Cxx, this way you can have
100% duty cycle and you are distributing data (low power) rather than
switching all those FETS uselessly. What's more the system could be
extended by adding rows without affecting display brightness. As mux
methods do.
                                       ray gardiner

{Quote hidden}

>> Hi all LED matrix fans,
>>
>> A few comments.
>>
>> Large Backlit LCD displays are available and might be suitable
>> in some circumstances.
>>
>> To minimise the number of drivers required you should reorganise
>> your matrix into as close to a square as possible electrically.
>>
>> For 8 x 96 you have 768 LEDs (sqrt = 27.7...) 'nice' numbers
>> are 24 x 32 which would give you a 1:24 multiplex with 32
>> collumns.  This will be a total of 56 drivers as opposed
>> to the 104 with the skinny display layout.  About half the number.
>
>True it's 32 cathode drivers. Each now has to sink 32*20ma = 640ma. That's
>more than 1/2 AMP. Packaging comes into play then. Of course it's easy
>to find power MOSFETs that can sink that kind of current, but then you
>have to wire each one individually. Plus you still need a controller to
>select which one(s) are on...
>
>>
>> The multiplex time and max current are altered by about 3 (better
>> or worse depending on which way you were planning to drive the
>> skinny arrangement)
>>
>> Now the problems are:
>>
>> No longer quite as logical display arrangement
>
>Not a big deal.
>
>> Possibly more high current drivers.
>
>This is the killer in my estimation.
>
>> Slightly more code.
>
>Just a bit...
>

Ray Gardiner, Shepparton, Victoria 3630,  Australia,   spam_OUTrayKILLspamnetspace.net.au

1996\11\13@103432 by Byron A Jeff

'LED matrix multiplexing (eyes & duty cycles, MAX 7'
1996\11\13@210255 by Zhahai Stewart

> Zhahai Stewart <RemoveMEzhahaiRemoveMEEraseMEHISYS.COM> wrote:
>
> > Anybody else have any experience with such a stretched out
> > multiplexing cycle?  I presume it would work (at the 48 KHz
> > pulse/500 HZ cycle you suggest to avoid flicker), but be
> > fairly dim.
>
> The human eye is more sensitive to peak brightness levels than
> it is to average levels; in my experience a 1/10 duty cycle
> looks about half as bright as a 1/1 duty cycle at the same
> peak current.

Given the highly non-linear response of the eye (closer to log, I
believe), I have a hard time knowing what half as bright is.  As
bright as the same LED at half the current?

How about this: What duty cycle at 20 ma tends to approximate the
brightness of an identical LED at constant X ma (eg: 5ma)?  This
should allow an A/B sort of test: set the constant current then
increment/decrement the duty cycle to match - or vice versa.

I'm certain this experiment has been done many times.  Anybody know
the results (or have a ready way to test this now?)

====

As for the LED matrix, I think the Maxim 7219 is very interesting, if
the price is reasonable.  One such chip would handle *everything* for a
single 8x8 LED block: 8 anode drivers, 8 cathode drivers, internal
clock and multiplexing, 8x8 internal RAM, serial shift register,
current limiting (no R's needed even).  It even has brightness
controls in 16 levels (as well as current set by one resistor).

I had seen the chip mentioned (Scott Edwards?) for controlling
7-segment LEDs (up to 8 of them), but didn't know it could also be
configured to control LED matrixes (by disabling the internal
BCD-to-7-seg decoding).

Only problem (other than price and availability) is that the peak
current is <40ma, typ 37ma.  This is less than half the peak for the
LED blocks (80 or 100ma).  I could live with that; close enough.

Thanks for the pointer, folks!  (Anybody got a source for a dozen or
so at good prices?)
    Zhahai

@ Zhahai Stewart       KILLspamzhahaispamBeGonehisys.com
@ A Meme Gardener      http://rainbow.rmii.com/~hisys/zhahai.html
@ Standard Disclaimer  YMMV - Your Maya May Vary

1996\11\14@024221 by Matthew Mucker

1996\11\14@040921 by Shel Michaels

'Yet another LED project'
1996\11\14@173902 by W. Lee Vick, Jr.

PIC.gurus,

       I also have a little LED project and was looking for some help with
it. I'd like to build a box which determines the order of finish of a pine
box derby (small wooden cars about 7" by 3" which run down a slotted track)
race. Ideally there will be one micro controlling things, 6 sensors (one for
each lane in the race), and 6 7-segment LED's which will show the position
in which the cars finished, and a button for resetting the system for the
next race. Thanks to info on the 595 I've figured out how to use it for
displaying the race results (or whatever else I want to display). My
questions are about the micro,the sensors, and the LED's:

       1. Can anyone recommend a good IR TX/RX pair which is small, cheap,
and will work over distances of about 3". Also, how do I wire this thing up?
Do I just treat it as a normally open switch?

       2. Any recommendations for 7-segment LED's? Ideally they'd have
current limiting resistors built in (to save wiring - I'm just an engineer
so my wire-wrapping skills are very suspect), be cheap (a recurring theme -
hey, this is for the Cub Scouts and they're not rich), and be as big as
possible (and no, I don't want to pay $5-10US each for 3" high versions).

       3. I figure I need about 14 I/O pins, maybe an INT, and a timer or
two. Which PIC should I use?

       I thank you, and if I can get all this working then the little Cub
Scouts thank you.

                                       Cheers,

                                       Lee.

************************************************************************
* Lee Vick           *   I had a nightmare that I was in an elevator   *
* leevickspamti.com     *   with Kenny G and Michael Bolton, a gun, and   *
* +1 713-274-2241    *      just one bullet... So I shot myself.       *
************************************************************************
* Standard disclaimer: TI as an organization is much too smart to      *
*                      to agree with anything I have to say.           *
************************************************************************

1996\11\14@192940 by Steve Hardy

> From: "W. Lee Vick, Jr." <RemoveMEwlvickspamBeGoneRemoveMEmicro.ti.com>
>
> PIC.gurus,
>
>         I also have a little LED project and was looking for some help with
> it. I'd like to build a box which determines the order of finish of a pine
> box derby (small wooden cars about 7" by 3" which run down a slotted track)
> race. Ideally there will be one micro controlling things, 6 sensors (one for
> each lane in the race), and 6 7-segment LED's which will show the position
> in which the cars finished, and a button for resetting the system for the
> next race. Thanks to info on the 595 I've figured out how to use it for
> displaying the race results (or whatever else I want to display). My
> questions are about the micro,the sensors, and the LED's:
>
>         1. Can anyone recommend a good IR TX/RX pair which is small, cheap,
> and will work over distances of about 3". Also, how do I wire this thing up?
> Do I just treat it as a normally open switch?

Since you work for TI (I assume Texas Instruments) they make optoelectronic
devices like this - you should take advantage of your employer's resources.
My employer makes tape drives.  These contain such sensors for determining
whether the tape is loaded.  Unfortunately, I have no idea who actually
makes the sensors.

>
>         2. Any recommendations for 7-segment LED's? Ideally they'd have
> current limiting resistors built in (to save wiring - I'm just an engineer
> so my wire-wrapping skills are very suspect), be cheap (a recurring theme -
> hey, this is for the Cub Scouts and they're not rich), and be as big as
> possible (and no, I don't want to pay $5-10US each for 3" high versions).

A bit optimistic price-wise unless you can find some surplus.  HP make
LED displays.  I got HDSP3400's which are reasonably cheap, a few cm
high and good efficiency.  Current limiting resistors not built-in so
you should use resistor packs if wiring is a problem.

Forget wire wrapping!  Making a PCB is so easy these days.  But first,
prototype the circuit on a breadboard.

>
>         3. I figure I need about 14 I/O pins, maybe an INT, and a timer or
> two. Which PIC should I use?

Well you don't need a timer if you are only interested in the _order_
of events, unless you need an overall timeout in case one of the cars
goes "off the rails".  You don't even need interrupts because the PIC
is fast enough to do everything by polling.  You just set up one humungous
program loop which updates and multiplexes the display, queries the
start button and reads the sensors as appropriate.  The number of I/O
pins is a bit of a killer otherwise you could use an 18-pin device.  You
will have to go for a 28-pinner such as 16C73.

Because of the simple application (not timing or interrupt critical) it
would be easy for you to completely test the software operation using
MPSIM.  This would almost guarantee that you would only have to burn the
EPROM once.

{Quote hidden}

>
>         I thank you, and if I can get all this working then the little Cub
> Scouts thank you.
>
>                                         Cheers,
>
>                                         Lee.
>
> ************************************************************************
> * Lee Vick           *   I had a nightmare that I was in an elevator   *
> * KILLspamleevickspamBeGoneti.com     *   with Kenny G and Michael Bolton, a gun, and   *
> * +1 713-274-2241    *      just one bullet... So I shot myself.       *
> ************************************************************************
> * Standard disclaimer: TI as an organization is much too smart to      *
> *                      to agree with anything I have to say.           *
> ************************************************************************
>

I would have lined them up and plugged both of 'em at once.

Regards,
SJH
Canberra, Australia

1996\11\15@002319 by Tony Matthews

1996\11\15@062248 by efoc

'Caller ID (was Re: LED matrix multiplexing (Correc'
1996\11\15@083052 by Hank Gupton

1996\11\15@083717 by Louis A. Mamakos

'LED matrix multiplexing (Correction !!!)CNID'
1996\11\15@085002 by Hank Gupton

'Yet another LED project'
1996\11\15@093622 by W. Lee Vick, Jr.

Steve,

       A few comments on your comments (for you and others to comment on)...

>>         1. Can anyone recommend a good IR TX/RX pair which is small, cheap,
>> and will work over distances of about 3". Also, how do I wire this thing up?
>> Do I just treat it as a normally open switch?
>
>Since you work for TI (I assume Texas Instruments) they make optoelectronic
>devices like this - you should take advantage of your employer's resources.
>My employer makes tape drives.  These contain such sensors for determining
>whether the tape is loaded.  Unfortunately, I have no idea who actually
>makes the sensors.

       Well, TI is HUGE and I don't work anywhere near anyplace where they
make these sensors. It's not like we have a company store where we can go
and pick up sensors, chips, laptops, or missiles cheap (TI makes all those
things and more). One would hope it would be a little easier to get things
from inside but in companies as big as this that's not always possible.

{Quote hidden}

>>         2. Any recommendations for 7-segment LED's? Ideally they'd have
>> current limiting resistors built in (to save wiring - I'm just an engineer
>> so my wire-wrapping skills are very suspect), be cheap (a recurring theme -
>> hey, this is for the Cub Scouts and they're not rich), and be as big as
>> possible (and no, I don't want to pay $5-10US each for 3" high versions).
>
>A bit optimistic price-wise unless you can find some surplus.  HP make
>LED displays.  I got HDSP3400's which are reasonably cheap, a few cm
>high and good efficiency.  Current limiting resistors not built-in so
>you should use resistor packs if wiring is a problem.

       OK, what I meant to say was that I can live with 1" high LED's but
if someone happened to know where I could get 2" for the same price, I'd be
happy to hear that. Define reasonably cheap for those HDSP3400's.

{Quote hidden}

>>         3. I figure I need about 14 I/O pins, maybe an INT, and a timer or
>> two. Which PIC should I use?
>
>Well you don't need a timer if you are only interested in the _order_
>of events, unless you need an overall timeout in case one of the cars
>goes "off the rails".  You don't even need interrupts because the PIC
>is fast enough to do everything by polling.  You just set up one humungous
>program loop which updates and multiplexes the display, queries the
>start button and reads the sensors as appropriate.  The number of I/O
>pins is a bit of a killer otherwise you could use an 18-pin device.  You
>will have to go for a 28-pinner such as 16C73.

       Right, I want the timer so I can set up a loop to shift the current
data I want to display out to the display circuitry and then latch it in -
this loop would be run every half second or so. Start up the system with
dashes displayed where the numbers go, start the timer routine, then all I
have to do is change some RAM locations and the display will take care of
itself. I COULD always do this in the main loop, but I'd rather loop on
polling the lane sensors to keep the resolution small.

>> ************************************************************************
>> * Lee Vick           *   I had a nightmare that I was in an elevator   *
>> * @spam@leevickSTOPspam@spam@ti.com     *   with Kenny G and Michael Bolton, a gun, and   *
>> * +1 713-274-2241    *      just one bullet... So I shot myself.       *
>> ************************************************************************
>
>I would have lined them up and plugged both of 'em at once.

       Thought of that. But there is the possibility the bullet would
deflect and not handle the one in the back. This is one where ya gotta go
with the worst case scenario. ;-)

       Thanks!

                                       Cheers,

                                       Lee.

1996\11\15@113546 by fastfwd

W. Lee Vick, Jr. <PICLISTspamBeGonespamBeGoneMITVMA.MIT.EDU> wrote:

> I'd like to build a box which determines the order of finish of
> a pine box derby (small wooden cars about 7" by 3" which run down a
> slotted track) race. Ideally there will be one micro controlling
> things, 6 sensors (one for each lane in the race), and 6 7-segment
> LED's which will show the position in which the cars finished, and a
> button for resetting the system for the next race.

Lee:

It's been done.  If you're only interested in HAVING one of these
things, rather than in BUILDING it, call John Shreffler at New
Directions, Inc.  He sells something called "The Judge"... LCD timer;
2- to 8-lane capability; 1st, 2nd, and 3rd-place indicators, etc.

New Directions can be reached at 703 319 0840.

-Andy

Andrew Warren - spamBeGonefastfwdix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499

1996\11\16@081521 by Matthew Mucker

1996\11\19@003448 by Barry Bine

'Searching for source of LED backlight 40x2 LCD mod'
1996\11\19@043852 by NEIL GANDLER

'LEDs revisited'
1996\11\19@231243 by Matthew Mucker

'Searching for source of LED backlight 40x2 LCD mod'
1996\11\21@211935 by Kalle Pihlajasaari

Hi Neil,

>  I am searching for a distributor of led backlight LCD modules 40x2.
> Distributors with a good selection. The 40x2 modules from Digi-key
> have crazy viewing angles. I just learned the $50 hard way. I
> prefer sources that have reasonable prices in small quantities (~$50)
>  What would also be helpfull is an LCD module with seperate LED
> connections. The above mentioned module has its LED GND connected
> to system ground. I would like to use my low side driver (DS75452)
> to control brightness, through my PIC PWM output. I would appreciate
> any help.

A few weeks ago I was quoted a onesies price of US$235 for a 40 x 2 LCD with
a transflective setup (works with the Backlight off) from the local chapter
of AVNET a very large component house.  The local chapter is called AVNET Kopp
but only because it merged with Kopp last year.

I don't know of details for any other countries but can make call to find out
if you send me e-mail.

Cheers
--
Kalle Pihlajasaari     spam_OUTkalleSTOPspamip.co.za
Interface Products     P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750     Fax: 402-7751

'LEDs revisited'
1996\11\22@055619 by fastfwd

Matthew Mucker <RemoveMEPICLISTspamMITVMA.MIT.EDU> wrote:

> In issue 31 (Feb. 1993) of Circuit Cellar Ink, Tom Cantrell
> describes a part by HP-- the HDSP-211x.  The '211x is an
> eight-character LED display. Each character is made of an array of
> 5x7 LEDs.
> ....
> The article is three years old, but if the part is still available,
> even if it's expensive, it's GOTTA be cheaper than all the support
> circuitry that would be needed for individual drivers.

Matt:

I wouldn't bet on it; last time I checked, those things cost $20-$30
each, in quantity.

-Andy

=== Andrew Warren - TakeThisOuTfastfwdspamRemoveMEix.netcom.com                 ===
=== Fast Forward Engineering - Vista, California          ===
===                                                       ===
=== Custodian of the PICLIST Fund -- For more info, see:  ===
=== http://www.geocities.com/SiliconValley/2499/fund.html ===

1996\11\22@141311 by Eddie Starling

This HDSP-211x sounds like what I was looking for. Does anybody know where I can get it in single quantities. Also, I would like a larger display, does anybody know of one that can be had in single quantities?

Eddie Starling
(516)549-6066
KILLspamedstarspamspam_OUTix.netcom.com

----------
From:   Matthew Mucker[SMTP:mmuckerRemoveMEAIRMAIL.NET]
Sent:   Tuesday, November 19, 1996 1:19 PM
To:     Multiple recipients of list PICLIST
Subject:        LEDs revisited

To the person who is building an LED caller id display--

In issue 31 (Feb. 1993) of Circuit Cellar Ink, Tom Cantrell describes a
part by HP-- the HDSP-211x.  The '211x is an eight-character LED display.
Each character is made of an array of 5x7 LEDs.  It's a 28-pin DIP part
that includes all the driver circuitry to display ASCII characters-- you
could even do the caller's name!  It's available in red, yellow, and green.
It allows custom character creation.  It is driven with a parallel
interface.  The article does not go into technical detail, but it appears
from a diagram that the pins are  labelled !RD, !WR, D0-D7, A0,A2, A3, A4,
!FL, !CE, !RST, CLK and CLS.

The article is three years old, but if the part is still available, even if
it's expensive, it's GOTTA be cheaper than all the support circuitry that
would be needed for individual drivers.  Plus, the interface will be a lot
easier, cutting your development time and costs.

Let me know what you find out.

-Matt


P.S. The HDSP-250x is the same part but is 7mm high, versus 5mm for the '211x.



 "DOS Computers manufactured by companies such as IBM, Compaq, Tandy, and
millions of others are by far the most popular, with about 70 million
machines in use wordwide. Macintosh fans, on the other hand, may note that
cockroaches are far more numerous than humans, and that numbers alone do
not denote a higher life form."

'LED matrix multiplexing (eyes & duty cycles, MAX 7'
1996\11\22@141714 by vince

'caller-id, was Re: LED matrix multiplexing (Correc'
1996\11\23@213824 by aab

>    Here in North America, caller ID information is sent as standard 1200 baud
>    ASCII text between the first and second ring.  The signals are exactly like
>    the ones used by your 1200 baud modem.

>I haven't used a 1200bps modem in about 15 years.  Can you even put a modern
>modem (ie, the 2400bps ones you can get for $10 surplus?) into a dedicated
>1200bps mode where it won't need to train/etc before receiving digits?

Modern modems decode caller id directly. The tones occur between the
first and second ring so no retrain is necessary.

The caller id decoder kits available consist of a Motorola MC145447P
caller id decoder chip and a MAX232 RS-232 driver. The 145447 could
be hooked to a pic software or hardware UART (there I mentioned PICs :-)


--
Best regards,
Andy Burgess
EraseMEaabSTOPspamRemoveMEcichlid.com

1996\12\14@004041 by Todd Peterson

'HELP with an LED Driver'
1996\12\16@155859 by Scott Horton

1996\12\16@172219 by Zhahai Stewart

> I am using a PIC16C84 to drive some 7 segment LED displays.  My problem
> is that the LED's are those BIG (3 inch) ones and each segment needs
> 40mA.  I was going to use a 2803 to drive them but with all 7 segments
> on, it looks like the power was too high.

> Can some of you suggest the best (simplest/cheapest) way to drive these
> LED's.

You could use multiple ULN2803's or ULN2003's, keeping the package
dissipation within bounds on each;  (ie: Don't use all channels per pkg).
They're cheap.  {For any reader who is unfamiliar, there are 8/7 channel
DIP packaged darlington low side drivers.)  This may be closest to your
current design (no pun intended) and thereby simple in that way; also
cheap.

You could consider the the MAX7219, which will handle everything for up
to 8 zeven-segment-plus-decimal LED displays.  It has high side drivers,
low side drivers, BCD-7 segment decoders, oscillator, current limiters,
RAM for the BCD, intensity modulation via PWM, shift register input
(fewer pins).  Around $8 in small quantities, US.  I believe that
Harris/Intersil have a similar parallel interfaced chip in the ICL7218.
Being N-way multiplexed (for N digits), this may be less bright than you
wish, tho you can probably up the peak current some to compensate.  This
may be the simplest, in that one chip and a single current setting resistor
handles up to 8 digits; you don't even need current limit resistors per
segment.  (You can also use the MAX7219 in direct undecoded mode, with
individual control of each segment).  Check the Maxim web pages.

Or you could substitute the TI TPIC6B595 8 bit SIPO latched shift register
with low side drivers; I think these can handle your 40ma / segement
continuous current, unlike the ULN2803.  Again, fewer pins needed, but
you need to handle multiplexing the high side, or use one per digit
unmultiplexed.  This is back to your earlier design, but with a shift
register/latch with more drive.  Check the Texas Instruments web pages.
   Zhahai

@ Zhahai Stewart       spam_OUTzhahaiRemoveMEEraseMEhisys.com
@ A Meme Gardener      http://rainbow.rmii.com/~hisys/zhahai.html
@ Standard Disclaimer  YMMV - Your Maya May Vary