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'LED Moving Message Display'
1999\08\01@185915 by Jonathon Doran

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> Thanks, that's a start, but not quite what I had in mind...looking for a PIC
> or similar microcontroller-driven set of multiplexed LEDs to allow roughly a
> 7 x 80 pixel field to be controlled.  Perhaps use a Hitachi LCD display and
> a few buttons for operator interface.  Any other suggestions will be greatly
> appreciated.

How big do you want it?  The HCMS 2975 has a 7*80 field :-)  I asked about
this earlier on the list, with no response so far.

But seriously, you might want to build your display the way they did.  A
320 bit shift register, with some latches.  Serially clock your data into
the shift register, then latch the display.  Shifting 5*7=35 bits and then
latching will cause the display to scroll.

The problem I'm running into with my displays (and I believe all my problems
are now related) is that current surges from the LEDs are causing my PIC to
brown out.  <sigh> HP recommends splitting the supplies, but when you have
pins like:
       Vled
       Vlogic
       GND

on the smaller displays, I have no idea how to wire them up without causing
ground loops.  Surely HP wasn't asking me to connect the grounds of two
different supplies together.  Perhaps they were...

Returning to our original subject, consider using separate supplies.

Jon Doran

1999\08\01@194729 by l.allen

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Sorry...
error
Whoop whoop .. Pull Up Pull Up

The Matrix Cathodes are driven off port D... port C is used for the
SPI interface to the RTC.
Lance Allen
Uni of Auckland
New Zealand

1999\08\01@221911 by Bob Blick

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Hi Bill,

You'll need 80 outputs. There are all-in-one shift registers with powerful
outputs, you'll probably need to get those from the manufacturer as samples
or order a tube of them. Or you could use 10 ser-par shift registers and 80
transistors to accomplish the same thing(or a bunch of darlington arrays).

Then you'll also need a 1 of 7 sequenced output, maybe out of a 4017 type
counter with 7 very very strong transistors.

The idea is to present 80 outputs, wait, then blank, sequence to the next
horizontal line, and present the next 80 outputs, etc.

A lot of work, but perhaps you have lots of time on your hands.

Remember that your displays and your drivers must match,
polarity-wise(unless you use 560 discrete LEDs). That's sort of the key to
a project like this.

Cheerful regards,
Bob



At 06:43 PM 8/1/99 -0400, you wrote:
>Thanks, that's a start, but not quite what I had in mind...looking for a PIC
>or similar microcontroller-driven set of multiplexed LEDs to allow roughly a
>7 x 80 pixel field to be controlled.  Perhaps use a Hitachi LCD display and
>a few buttons for operator interface.  Any other suggestions will be greatly
>appreciated.

1999\08\01@222326 by Bill Kichman

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Hey, that's not bad, I will have to check it out.  Kinda takes the fun outta
things though ;-)
Didja happen to see how big it is physically?

Bill K.

{Original Message removed}

1999\08\01@232057 by Jeff King
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Bill:

The sign at sam's club is the beta brite. They are nice, and you can
program them with RS-232. Check out:

http://betabrite.com/Pages/betabrite.htm

and that should have most of the info.

-Jeff wb8wka


Bill Kichman wrote:

> Hey, that's not bad, I will have to check it out.  Kinda takes the fun outta
> things though ;-)
> Didja happen to see how big it is physically?
>
> Bill K.
>
> {Original Message removed}

1999\08\02@042248 by Brian Jones

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Funny - I too was looking at one of these. Last time is was in
Silicon Valley I picked up 12 7*5 led arrays so figured a 7*60 sign
would be fun. Each array needs 12 pin drivers (ie 144 pins total).
Rather than MUX I thought of using 5450 serial parallel LED drivers
(these are 2 pin in 34 pin out) so I could use 5 and have
software/EEPROM do all the work. That would leave enough pins
on the 16F84 for a serial eeprom to hold the message data and
scrolling options.

I'm not a hardware guy so does this make sense - is there a better/
cheaper way.

Brian
Brian E Jones
Centre for Java Technology
IBM HURSLEY

1999\08\02@095408 by miked

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> The problem I'm running into with my displays (and I believe all my
> problems are now related) is that current surges from the LEDs are causing my
PIC
> to brown out.  <sigh> HP recommends splitting the supplies, but when you
> have
> pins like:
>         Vled
>         Vlogic
>         GND
> on the smaller displays, I have no idea how to wire them up without
> causing ground loops.  Surely HP wasn't asking me to connect the grounds of tw
o
> different supplies together.  Perhaps they were...
>
> Returning to our original subject, consider using separate supplies.
In this case yes the two supplies would have ground common. One V+ to
Vled and the others to Vlogic.
We had a product that we tapped the Ni-Cad pack(not recommended) one
cell down for the logic supply to keep the LED swiching noise out.

1999\08\02@102613 by Wagner Lipnharski

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Ok, now, don't forget about the LED intensity.

Even if you apply twice the LED nominal current (the max peak
recommended by the manufacturer), you can not make it bright enough to
see at the day light if you apply current for less than 10% of the time.

If you are planning to time share current, in a scanning technique,
remember this.

My personal experiments with scanning display, ended in a maximum of
1/8, (1 on, 7 off), using 40% more than the nominal current, at a rate
bigger than 200Hz.

If you will build a display like that, I think you could go a little
further, and do it not only horizontal shifting message, why not do it
scroll vertical, or zooming, dropping, pouring, and sometihng like that?

The only trick here is to have a memory bit mapped space, and your
processor can set or reset any bit into that memory. That block of
memory is then sent (10 or 20 times a second) to the LED driver system,
that will copy that to the LEDs, each bit corresponding to a specific
LED.

If you think about it, it is not that difficult.

But remember about the scanning, a 80 x 8 led matrix would require one
whole horizontal line (row) of LEDS turned ON all the time, so you would
need a 80 drivers to constantly feed the columns.   Considering a 50%
increase in the LED current, lets say from 20 to 30mA, you would need a
power supply around 30mA x 80 = 2.4 Ampers, just for the LEDS consume.

Wagner

1999\08\02@112245 by brad

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Wagner Lipnharski wrote:
>
> Ok, now, don't forget about the LED intensity.
>
> Even if you apply twice the LED nominal current (the max peak
> recommended by the manufacturer), you can not make it bright enough to
> see at the day light if you apply current for less than 10% of the time.

Agreed

> If you are planning to time share current, in a scanning technique,
> remember this.
>
> My personal experiments with scanning display, ended in a maximum of
> 1/8, (1 on, 7 off), using 40% more than the nominal current, at a rate
> bigger than 200Hz.

Yep.. had to do the same..

> If you will build a display like that, I think you could go a little
> further, and do it not only horizontal shifting message, why not do it
> scroll vertical, or zooming, dropping, pouring, and sometihng like that?

Not difficult to do.

{Quote hidden}

I am doing that currently with a 16c66 running at 8Mhz.. Driving a 96x7
led matrix.
Using non latched shift registers (74164) from memory.. driving uln2003
darlingtion arrays thru 300Ohm resistors for the columns and the rows
driven from 2N2955 Transistors..
Because the shift registers are not latched, you must have the rows off
while shifing data in.. A pig of a design really, but it's someone elses
board and just my controller.
Using 96 bytes of contiguous ram for the display buffer, and most of the
remaining ram for comms buffers.. effects buffers and the like.
Everything is updated real-time and is commanded thru an rs485 link
at 9600 baud.
The display is refreshed thru a real time interrupt, and the serial data
to the display is bit bashed as the SPI and UART are mutually exclusive.
Also, given that each bit has to be masked from the relevant byte, it's
not that much quicker.

The characters are stored in lookup tables styled along the lines of
Don McKenzies old Z80 code. (Hi Don!) tho had to put them across 2 banks
so as not to cross a bank boundary... Bloody banks..

The Character generation routine is very very very tight hand coded
assembler, because when it is triggered after a display line refresh
it only JUST has time to finish before the next refresh is due. So
tight is the timing.
The display ram is locked by the char gen routines using a semaphore
to prevent the isr from touching it, should the char gen take to long.
Otherwise the display glitches and presents a tearing type of picture.

Anyway.. writing the code only took me about 2 days on and off, and
it was Hugely educational when it came to shaving 80 or so cycles from
routines to stop jitter and glitching..

The effects are the fun part.. Only completed the slide/wipe and roll
so far.. I'm looking at external ram for some more spiffy effects..
It's fun to see how far you can push a $13 chip, when your competition
is doing it with a full blown HC11 with 32K Ram & Rom at 16Mhz..
But then they will write in C won't they :p)

Cheers...
Brad...

PS. If you want to look at CHEAP, and very good led signs.. take a look
at what out South African buddies are up to. I have gotta say, those
years of trade embargoes have turned South Africa into a very clever
continent.

1999\08\02@121026 by Mike Keitz

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On Mon, 2 Aug 1999 13:40:39 +1000 Gennette Bruce
<spam_OUTbruce.gennetteTakeThisOuTspamTAFE.NSW.EDU.AU> writes:
>Here is a simple idea that works really well - it uses just 3 diodes
>and 1
>extra capacitor.
[...]
>The really cool thing is that the outputs from the 2 diodes are
>completely
>isolated from each other

It doesn't quite work that way.  A diode with DC current flowing through
it acts like a small resistor to AC signals.  Also if one of the loads
changes greatly, the regulator's limited load regulation will appear at
the other output.

You'd be just as well off to forget the diodes and have seperate circuits
for the analog and digital sections that join only at the regulator's
output pin.  The ground circuits are likewise seperated.  This is a
standard good design practice.  In extreme cases, a RC or LC filter in
one of the circuits may be needed, but going to two regulators would be
better.


___________________________________________________________________
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1999\08\02@123348 by eplus1

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<BLOCKQUOTE AUTHOR=".....bruce.gennetteKILLspamspam@spam@TAFE.NSW.EDU.AU">> Here is a simple idea that works really well - it uses just 3 diodes and 1
extra capacitor.
<SNIP>
The really cool thing is that the outputs from the 2 diodes are completely
isolated from each other.
</BLOCKQUOTE>

<BLOCKQUOTE AUTHOR="Mike Keitz">
It doesn't quite work that way.  A diode with DC current flowing through
it acts like a small resistor to AC signals.  Also if one of the loads
changes greatly, the regulator's limited load regulation will appear at
the other output.
</BLOCKQUOTE>

I don't think that either is entirely correct. No, the two supplies are not
"entirely" isolated, but for the negative part of the AC signal, the current
will be prevented from flowing into the other circuits diode (since that
circuits capacitor will temporarily keep that end of the diode at a higher
voltage) and so you do get at least "clipping" of the noise. The positive
part of the AC gets chopped by the diode connected to the circuit that is
producing it as for that instant, it is reversed biased (relative to the
regulated supply) and the circuit is being powered from the combination of
the cap and the positive spike. Exceptions include the (small) voltage
required to reverse bias the diodes and the (minor) discharge of the caps
when the diodes are reverse biased.

Please correct me if I am wrong.

James Newton, webmaster
http://get.to/techref
jamesnewtonspamKILLspamgeocities.com <.....jamesnewtonKILLspamspam.....geocities.com>
1-619-652-0593 phone

1999\08\04@080148 by Tim

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Using common grounds (-ve wire) from to supplies is a common method in micro
based alarm systems and rearly causes problems. I have however beenadvised
by a client that in a CCTV system, 2 cameras in separate buildings cabled
back to 1 monitor with coax had a problem caused by the building earth
stakes being at different potentials causing the camera to blow up.

Never encounted the problem myself though.

Tim Norton
{Original Message removed}

1999\08\05@215303 by Bill Kichman

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Yes, I do building power distribution systems in my day job.  We never allow
separate, isolated grounding to exist due to these problems.  Wned a process
vendor requests an  "isolated" ground rod, he gets a ground rod outside the
building, and a copper #4/0 stranded conductor extended to the main building
ground (loop, counterpoise, building steel, pipe, etc.).  In the case you
describe, there was easily chance for a serious ground potential and ground
currents.  The solution would've been to ground the coax shield at the
building entrance.
For what it's worth...

Bill Kichman, P.E.
Cornwall, PA USA
{Original Message removed}

1999\08\05@215923 by Bill Kichman

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Does anybody have any good leads on really cheap LEDs??  I want to build
this 7 x 80 led moving text sign, but don't want to go broke buying the 560
leds.  Are modules cheaper?  Are they available in 4" height?
{Original Message removed}

1999\08\05@231516 by Tony Nixon

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picon face
Bill Kichman wrote:
>
> Does anybody have any good leads on really cheap LEDs??  I want to build
> this 7 x 80 led moving text sign, but don't want to go broke buying the 560
> leds.  Are modules cheaper?  Are they available in 4" height?

The modules are definitely cheaper. I don't have a price on hand though.
Even considering time savings on construction they must be a better
alternative.

I've used upto 50mm. I don't know if they come larger.

You can get matrix displays with zero display current with mechanical
switching modules with good daylight visibillity. These (that I've seen)
come in sizes to 16" in height. I'd hate to see the price though :-(

--
Best regards

Tony

"COMING SOON"
A Parallax to PIC source code converter.

http://www.picnpoke.com
Email ???

1999\08\06@003537 by Bob Blick

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At 09:57 PM 8/5/99 -0400, you wrote:
>Does anybody have any good leads on really cheap LEDs??  I want to build
>this 7 x 80 led moving text sign, but don't want to go broke buying the 560
>leds.  Are modules cheaper?  Are they available in 4" height?

HSC Electronics in Santa Rosa, CA has 4 or 5 inch modules for about 5
dollars if I recall. They don't do mail order, but if they have them at
that price you ought to be able to find them elsewhere for a similar price.
Perhaps http://www.allcorp.com or Marlin P. Jones?

Cheers,
Bob

1999\08\06@165037 by Bill Kichman

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Hey thanks I 'll check it out.

Bill K.
Cornwall, PA USA
-----Original Message-----
From: Bob Blick <EraseMEbblickspam_OUTspamTakeThisOuTSABER.NET>
To: PICLISTspamspam_OUTMITVMA.MIT.EDU <@spam@PICLISTKILLspamspamMITVMA.MIT.EDU>
Date: Friday, August 06, 1999 12:36 AM
Subject: Re: LED Moving Message Display


>At 09:57 PM 8/5/99 -0400, you wrote:
>>Does anybody have any good leads on really cheap LEDs??  I want to build
>>this 7 x 80 led moving text sign, but don't want to go broke buying the
560
{Quote hidden}

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