Searching \ for '[PIC] Best Pic for the job' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/microchip/devices.htm?key=pic
Search entire site for: 'Best Pic for the job'.

Exact match. Not showing close matches.
PICList Thread
'[PIC] Best Pic for the job'
2005\05\26@155743 by James

picon face

New to the whole pic thing. Got them blinking though. Here is my
question what is the best pic chip for the job.

1. Lowest power consumption pic
2. Run 6 to 12 Leds
3. Work on battery's - Like 4 double AA's
4. Can run some sort of clock program that is user programmable to turn
off and on at certain times. - Still trying to master the code on this
one, also I will take interface Ideas on this one. Could it be possible
to use jumper settings for this?

Thanks for the input - a humble new guy.

James

2005\05\26@161946 by Jan-Erik Soderholm

face picon face
James wrote :

> New to the whole pic thing. Got them blinking though.
> Here is my question what is the best pic chip for the job.
>
> 1. Lowest power consumption pic

Probably one of the "nanoWatt" models. Available in both
the PIC16 and PIC18 lines.

> 2. Run 6 to 12 Leds

A DIP16 or DIP18. 16F684/688/818/819 maybe ?

> 3. Work on battery's - Like 4 double AA's

Add a low power low dropout regulator. 5V or lower.

> 4. Can run some sort of clock program that is user
> programmable to turn off and on at certain times.

Are "times" real 24h clock ("wall clock") times ?
Or just "each 10 min" or something ?
Will it have some interface to set time and to enter
timestamps ? Keyboard ? Serial (from a PC) link ?

Add a 32k crystal to tmr1 and let the PIC sleep most of the
times. While awake, run on intosc for fastest startup
from sleep/lowest power.

> - Still trying to master the code on this
> one, also I will take interface Ideas on this one. Could it
> be possible to use jumper settings for this?

What should the jumpers configure ? What is "this" ?

Best Regards,
Jan-Erik.



2005\05\26@162204 by Dave Turner

picon face
Well, for low power consuption, you might want to try some of the new
nanowatt PICs.  I think the 16F87 and the 18F1320 both have this.

To run 6 to 12 LEDS, you will need 6 to 12 IO pins.  Also, you will
probably want a few more inputs and outputs for buttons, or jumpers.
Most of the PICs with more than 18 pins should cover this.

As for using jumpers for configuration, You would need some sort of
system to connect the pin to either ground or 5V, depending on the
jumper status.  I'm not sure if the pin reads high or low when just
disconnected.

I think nearly all of the PICs should cover all these requirements,
except the tiny 8 pin devices, and probably not the 18 pins (unless
you use strobing).

On 5/26/05, James <spam_OUTgogomagicTakeThisOuTspamcomcast.net> wrote:
{Quote hidden}

> -

2005\05\26@162358 by Shawn Tan Ser Ngiap

flavicon
face
> New to the whole pic thing. Got them blinking though. Here is my
> question what is the best pic chip for the job.
> 1. Lowest power consumption pic

The nanowatt series are supposed to use low power.. They come with internal
oscillators too... Also, look for the low power parts instead of the standard
parts..

> 2. Run 6 to 12 Leds

Any 18pin PIC has enough I/O lines to control 12 LEDs...

> 3. Work on battery's - Like 4 double AA's

Yeah, they can definitely work on batteries... and if you use the low power
parts, you may not even need 4x..

> 4. Can run some sort of clock program that is user programmable to turn
> off and on at certain times. - Still trying to master the code on this
> one, also I will take interface Ideas on this one. Could it be possible
> to use jumper settings for this?

Well... you could use the EEPROM to store user settings... You could use a
7seg display or LCD for the output.. but I'm not too sure what the jumpers
would be for... You could use pushbuttons and build a simple menu system...

Sounds a bit ambitious for a starter project though.. You might want to build
it bit by bit and learn things one at a time.. Good luck!!!

cheers..

--
with metta,
Shawn Tan

2005\05\26@163632 by Jan-Erik Soderholm

face picon face
Dave Turner wrote :

> To run 6 to 12 LEDS, you will need 6 to 12 IO pins.  Also, you will
> probably want a few more inputs and outputs for buttons, or jumpers.
> Most of the PICs with more than 18 pins should cover this.

As it was specifed, 18 would do.

> As for using jumpers for configuration, You would need some sort of
> system to connect the pin to either ground or 5V, depending on the
> jumper status.  I'm not sure if the pin reads high or low when just
> disconnected.

Internal pullup and jumpers to gnd.

With some clever technices you can get three "levels"
on each pin (high/low/open), or more using external
resistor networks.

> I think nearly all of the PICs should cover all these requirements,
> except the tiny 8 pin devices, and probably not the 18 pins (unless
> you use strobing).

Again, there wasn't enough in the "specs" to exclude 18-pins.

Jan-Erik.



2005\05\26@163808 by Bob Blick

face picon face
> 1. Lowest power consumption pic
> 2. Run 6 to 12 Leds
> 3. Work on battery's - Like 4 double AA's
> 4. Can run some sort of clock program that is user programmable to turn
> off and on at certain times. - Still trying to master the code on this
> one, also I will take interface Ideas on this one. Could it be possible
> to use jumper settings for this?
> Thanks for the input - a humble new guy.

If you are running a clock, then you need to run all the time, or have a
pic that can take a second crystal for realtime clock at 32.768 KHz. Your
real power consumption, especially if you run the LEDs even occasionally,
is not going to be affected much by your choice of PIC.

How about 2 or 3 AA batteries? Then you will not need a regulator(save
current that way too).

Since you are a beginner, do it as simply as possible, which means no
multiplexing of pins. Get a 40 pin PIC like the 16F877(A) or 18F452.

Cheers,

Bob



2005\05\26@164221 by John J. McDonough

flavicon
face
----- Original Message -----
From: "Dave Turner" <.....dave.w.turnerKILLspamspam@spam@gmail.com>
Subject: Re: [PIC] Best Pic for the job


> Well, for low power consuption, you might want to try some of the new
> nanowatt PICs.  I think the 16F87 and the 18F1320 both have this.

The 16LF87/88 will run down to 2 volts, so a 3 volt lithium cell could be
comfortable.  They have an onboard oscillator freeing up two more pins as
I/O, and the oscillator is programmable so you can manage the power
consumption even further.

> I think nearly all of the PICs should cover all these requirements,
> except the tiny 8 pin devices, and probably not the 18 pins (unless
> you use strobing).

He is only talking 6-12 LEDs plus a button or two.  An 18 pin part with an
onboard oscillator is going to have 15 or 16 pins available, depending on
whether you reuse !MCLR.  If you want to do ICSP and have obnoxious
circuitry on all pins you might get down to 13 I/O.  With two buttons,
that's still 11 LEDs.  If you insist on a crystal you are down to 9 LEDs,
and that's worst case, still in the 6-12 range.

--McD

2005\05\26@164948 by Mark Rages

face picon face
On 5/26/05, Dave Turner <dave.w.turnerspamKILLspamgmail.com> wrote:
> As for using jumpers for configuration, You would need some sort of
> system to connect the pin to either ground or 5V, depending on the
> jumper status.  I'm not sure if the pin reads high or low when just
> disconnected.

For minimum parts cound, enable the "weak pull-up" option and use
jumpers shorting to ground.   That costs an extra 50-400 uA per pin
grounded.  To save current, you could turn on the weak pull up before
you read the jumpers and back off afterwards.

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2005\05\26@171449 by Bob Ammerman

picon face
The OPs 'low-power' requirements are in significant conflict with
illuminating 6 to 12 LEDs.

Bob Ammerman
RAm Systems

2005\05\26@173034 by phil B

picon face
There are lots of techniques for multiplexing pins to
get more than 1 LED per pin.  Numerous microchip app
and design notes on this topic.  Look at how 7 seg
displays are done to get an idea (you may not need
drive transistors).  There was also a microchip
newsletter (iirc) article from about a year ago that
got a goodly number of LEDs per pin by using output L,
H and high Z (input) plus a bit of mental gymnastics.


My favorite answer is a 12F509 + 2 74HC595s (to drive
up to 16 LEDs) but I suspect thats not what is being
looked for.

Phil

--- "John J. McDonough" <.....mcdKILLspamspam.....is-sixsigma.com> wrote:
> {Original Message removed}

2005\05\26@174259 by Byron A Jeff

face picon face
On Thu, May 26, 2005 at 01:57:45PM -0600, James wrote:
>
> New to the whole pic thing.

Cool.

> Got them blinking though.

Excellent.

> Here is my  question what is the best pic chip for the job.

Fire away.
>
> 1. Lowest power consumption pic
> 3. Work on battery's - Like 4 double AA's

These two go together.

> 2. Run 6 to 12 Leds

This is incompatible with the first two goals. Unless you are doing
intermittent blinking LEDs, the LEDs will consume several of orders of
magnitude more of your battery power than the PIC ever will.

BTW any PIC with 18 or more pins should be able to handle that job.

> 4. Can run some sort of clock program that is user programmable to turn
> off and on at certain times. - Still trying to master the code on this
> one, also I will take interface Ideas on this one. Could it be possible
> to use jumper settings for this?

Of course. But as a first crack I would suggest doing a 3 button
up/down/select interface. Then you only need to read (and debounce) three
buttons to get the interface.

Also you'll find clocks tougher than you think. Any timer that's not
temperature compensated will drift. So they'll get out of time pretty
quick.

I have a rather complex sunrise/sunset outdoor light controller that has
many of the functions you require. No schematic (sorry!) but the code
can be found here: http://www.finitesite.com/d3jsys/clock.asm
You will find code for managing an LCD display, tracking a time for a
clock/calendar, and other goodies.

Hope it helps,

BAJ

2005\05\26@174607 by Byron A Jeff

face picon face
On Thu, May 26, 2005 at 05:10:54PM -0400, Bob Ammerman wrote:
> The OPs 'low-power' requirements are in significant conflict with
> illuminating 6 to 12 LEDs.

That was my first observation. The only way it could have been worse is
specifying a 9V battery for the power source.

One aside on my other post: my sunrise/sunset light controller drifts too.
I usually have to reset it at least once a month.

BAJ

2005\05\26@174722 by Byron A Jeff

face picon face
On Thu, May 26, 2005 at 02:30:33PM -0700, phil B wrote:
> There are lots of techniques for multiplexing pins to
> get more than 1 LED per pin.  Numerous microchip app
> and design notes on this topic.  Look at how 7 seg
> displays are done to get an idea (you may not need
> drive transistors).  There was also a microchip
> newsletter (iirc) article from about a year ago that
> got a goodly number of LEDs per pin by using output L,
> H and high Z (input) plus a bit of mental gymnastics.
>
>
> My favorite answer is a 12F509 + 2 74HC595s (to drive
> up to 16 LEDs) but I suspect thats not what is being
> looked for.

Phil,

It begs an interesting question. Why is that combo better than
a 28 or 40 pin PIC?

BAJ

2005\05\26@190859 by William Chops Westfield

face picon face
On May 26, 2005, at 1:36 PM, Jan-Erik Soderholm wrote:

>> To run 6 to 12 LEDS, you will need 6 to 12 IO pins.

To run 12 LEDs, you need 4 IO pins...

 :-)
BillW

2005\05\26@203456 by Andre Abelian

flavicon
face
Bob,

For low battery application 18LF452 is better.

Andre




-----Original Message-----
From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu] On Behalf Of
Bob Blick
Sent: Thursday, May 26, 2005 1:38 PM
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] Best Pic for the job

> 1. Lowest power consumption pic
> 2. Run 6 to 12 Leds
> 3. Work on battery's - Like 4 double AA's
> 4. Can run some sort of clock program that is user programmable to turn
> off and on at certain times. - Still trying to master the code on this
> one, also I will take interface Ideas on this one. Could it be possible
> to use jumper settings for this?
> Thanks for the input - a humble new guy.

If you are running a clock, then you need to run all the time, or have a
pic that can take a second crystal for realtime clock at 32.768 KHz. Your
real power consumption, especially if you run the LEDs even occasionally,
is not going to be affected much by your choice of PIC.

How about 2 or 3 AA batteries? Then you will not need a regulator(save
current that way too).

Since you are a beginner, do it as simply as possible, which means no
multiplexing of pins. Get a 40 pin PIC like the 16F877(A) or 18F452.

Cheers,

Bob



2005\05\26@204107 by Dwayne Reid

flavicon
face
part 1 1971 bytes content-type:text/plain; charset="us-ascii"; format=flowedAt 03:47 PM 5/26/2005, Byron A Jeff wrote:
> >
> > My favorite answer is a 12F509 + 2 74HC595s (to drive
> > up to 16 LEDs) but I suspect thats not what is being
> > looked for.
>
>It begs an interesting question. Why is that combo better than
>a 28 or 40 pin PIC?

I love questions like this <grin>.  Why indeed?

My usual responses:

1) I can use a smaller packaged PIC (6 or 8 pins if the only thing is to
read a few switches and drive LEDs).

2) I can place the LED drivers near the LEDs and connect with only 2 or 3
lines plus power and ground.  Handy if the PIC is located elsewhere.

3) I can drive the LEDs from an un-regulated supply and keep the PIC supply
nice and clean.  (this is a trick answer: unreg supply is about anywhere
from 3.3 to 6V if using 74hc595 or just about anything at all if using
TPIC6595)

3b) Can drive reasonable sized relays instead of LEDs if using TPIC6595.

4) 74hc595 are just SOooo darned inexpensive!  Drive 8 LEDs for 10 cents or so.

5) One of my boards has 40 status LEDs on it as well as 3- 7 segment
displays.  Also has 16 or so digital inputs (both binary and trinary).  All
driven with only 3 i/o lines from PIC.


No question: if this is a one-off hobbyist project that needs only 12 LEDs,
spend the extra dollars and go for a larger PIC.

But **I** would probably do it with a tiny PIC and shift registers simply
because that's what I'm used to doing for larger projects.  And I just
happen to have several hundred (or more) little (1" x 3") single-sided PCBs
that hold an 8 pin PIC, simple 5V zener PSU (with JFET discharge circuit),
2- trimpots wired for RC time measurements, 3- digital inputs, 2- TPIC6595
shift registers.  The PIC section can be snipped off, leaving the remainder
of the board with the 2- shift registers to connected to previous boards to
make a SR chain as long as needed.   They get used for all kinds of simple
projects.

dwayne

part 2 7298 bytes content-type:image/gif; name="L342A2-01.GIF"; (decode)


part 3 519 bytes content-type:text/plain; charset="us-ascii"; format=flowed

--
Dwayne Reid   <@spam@dwaynerKILLspamspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 21 years of Engineering Innovation (1984 - 2005)
 .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-
    `-'   `-'   `-'   `-'   `-'   `-'   `-'   `-'   `-'
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.


part 4 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2005\05\27@003753 by phil B

picon face
You beat me to it!  Well put.

I would also add that the 595s allow you add more LEDs
(or what ever) in units of 8 by chaining them.  No
real gymnastics needed, just pump the bits out via bit
bang SPI (which is only slightly more complex than
bsf/bcf).  There is a practical limit but its pretty
high.  I used them on an LED light stick design - I've
had as high as 128 working.  The bike light project in
the current Nuts and Volts could have benefitted from
this approach.

Another issue is board space.  A 40 pin PIC takes up a
lot more space than an 8 or 14 pin one.  A 40 pin PIC
seems like over kill to light up 32 LEDs.  

Phil

--- Dwayne Reid <KILLspamdwaynerKILLspamspamplanet.eon.net> wrote:

{Quote hidden}

> > --

2005\05\27@021053 by PicDude

flavicon
face
On Thursday 26 May 2005 04:30 pm, phil B scribbled:
> My favorite answer is a 12F509 + 2 74HC595s (to drive
> up to 16 LEDs) but I suspect thats not what is being
> looked for.
>
> Phil


Doesn't the 74HC595 not have the current output capability of a PIC?  IIRC it
was something like 5-6mA for the 74HC595, which IMO is not much for driving
LED's properly.  But of course, it depends on the specific LEDs and
application of the OP.

Cheers,
-Neil.


2005\05\27@021745 by vasile surducan
picon face
On 5/26/05, James <spamBeGonegogomagicspamBeGonespamcomcast.net> wrote:
>
> New to the whole pic thing. Got them blinking though. Here is my
> question what is the best pic chip for the job.
>
> 1. Lowest power consumption pic
> 2. Run 6 to 12 Leds

PIC16F630 or PIC16F676
6 pin PIC is more than enough for running 12 LED, without additional hardware.
Application with 16F628:
http://surducan.netfirms.com/conexclub/main.html


Vasile



> 3. Work on battery's - Like 4 double AA's
> 4. Can run some sort of clock program that is user programmable to turn
> off and on at certain times. - Still trying to master the code on this
> one, also I will take interface Ideas on this one. Could it be possible
> to use jumper settings for this?
>
> Thanks for the input - a humble new guy.
>
> James
>
> -

2005\05\27@025427 by phil B

picon face
The Fairchild 74HC595 datasheet specs a max current of
35mA per pin though I wouldn't get anywhere near that
with out a pretty gentle duty cycle.  The dip package
has a 600 mW limit, and the SO's is 500 mW.

I've run a number of tests on it because I was
concerned.  With all 8 outputs constantly driving LEDS
at 10 mA for 24 hrs there was very little heat
increase (a couple degrees F) so the 500 mW limit may
be conservative.  This was with both Fairchild and ST
parts.  Any kind of <100% duty cycle is going to help
here as well.

One thing to be carefull of is inrush current and
spikes on the clock and serial in pin.  I use a 1K
limiter and 100K to ground on both RCLK and SERIN.

Phil

--- PicDude <TakeThisOuTpicdude2EraseMEspamspam_OUTnarwani.org> wrote:
{Quote hidden}

> --

2005\05\27@030242 by At van Wijk

flavicon
face
Hoi Dwayne,

Do you use the "JFET discharge circuit" for empty-ing
your power cap? Or what else?

At van Wijk.


----- Original Message -----   From: "Dwayne Reid"

> ../, simple 5V zener PSU (with JFET discharge circuit),
> /..  dwayne



--
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.322 / Virus Database: 266.11.17 - Release Date: 25-5-2005

2005\05\27@035823 by PicDude

flavicon
face
I just checked the TI & Fairchild datasheets -- interesting that you work with
the "absolute maximum rating" of 35mA.   Though the Fairchild does not
specifically state a normal high and low output current, the TI datasheet
specs this as "+/- 6mA output drive", but also states an absolute max of
35mA.

I asking this because it's piqued my interest for future use.  I usually have
a self-coded PWM routine to allow dimming of the LEDs from 1/9 to 9/9
duty-cycle, and on a newer experiment, I'm trying to see if I can easily dim
different LEDs to different intensities.  If I can swing the current I need
when at 100% duty cycle, I'm trying to think of how intense the data output
(from the PIC to the shift register) could be to do software dimming.  I also
see it has an output-enable pin, which could be used for global dimming (at
the cost of 1 extra pin), but not for multiple-level dimming.  I'll have to
think about this some more...

Cheers,
-Neil.



On Friday 27 May 2005 01:54 am, phil B scribbled:
{Quote hidden}

2005\05\27@055453 by aslam jallali

picon face
just one remark from my own experience: make sure that your programmer support whatever PIC you use. If you are using an old type programmer make sure it support the new chip. In my case I have to spend an extra 35 bocks

               
---------------------------------
Discover Yahoo!
Get on-the-go sports scores, stock quotes, news & more. Check it out!

2005\05\27@060828 by Alan B. Pearce

face picon face
>Internal pullup and jumpers to gnd.

However this technique does not usually result in a "low power processor"
because of the way the internal pullups work.

2005\05\27@061835 by Alan B. Pearce

face picon face
>> The OPs 'low-power' requirements are in significant conflict with
>> illuminating 6 to 12 LEDs.
>
>That was my first observation. The only way it could have been worse
>is specifying a 9V battery for the power source.

<VBG> so the OP could add some switching regulator experience as well - but
then I am not sure if a 9V battery has a better watts/cubic cm than AA
cells.

>One aside on my other post: my sunrise/sunset light controller
>drifts too. I usually have to reset it at least once a month.

Sounds like time to add a radio clock - or have a photo cell that detects
the daylight time and sets midnight to the midpoint between sunrise and
sunset each night. Don't know if that would be accurate enough - maybe in
very low rainfall/cloud cover areas.

2005\05\27@062251 by Jan-Erik Soderholm

face picon face
Alan B. Pearce wrote :

> >Internal pullup and jumpers to gnd.
>
> However this technique does not usually result in a "low
> power processor because of the way the internal pullups
> work.

Only turn on wpu while checking the pin ?

Jan-Erik.



2005\05\27@063910 by Bob Ammerman

picon face

----- Original Message -----
From: "phil B" <philpiclistEraseMEspam.....yahoo.com>
To: "Microcontroller discussion list - Public." <EraseMEpiclistspammit.edu>
Sent: Friday, May 27, 2005 2:54 AM
Subject: Re: [PIC] Best Pic for the job


{Quote hidden}

At 10ma the Vol (low output voltage) of the 74HC is probably quite a bit
less than 1 volt. So, assuming worst case:

1 V * 10 mA * 8 = 8mW

Not much dissipation at all.

Bob Ammerman
RAm Systems

2005\05\27@064540 by Alan B. Pearce

face picon face
>> >Internal pullup and jumpers to gnd.
>>
>> However this technique does not usually result in a "low
>> power processor because of the way the internal pullups
>> work.
>
>Only turn on wpu while checking the pin ?

Yeah, someone else pointed that out too.

2005\05\27@065001 by Chris Emerson

flavicon
face
On Fri, May 27, 2005 at 11:45:26AM +0100, Alan B. Pearce wrote:
> >> >Internal pullup and jumpers to gnd.
> >>
> >> However this technique does not usually result in a "low
> >> power processor because of the way the internal pullups
> >> work.
> >
> >Only turn on wpu while checking the pin ?
>
> Yeah, someone else pointed that out too.

But then don't you have a floating input if the jumper's not in place?
That'll probably eat up more current than the weak pullup.

Chris

2005\05\27@075841 by Jake Anderson

flavicon
face
drive it low
if its jumpered it wont matter
if its unjumpered then enable wpu and check


{Quote hidden}

> --

2005\05\27@104414 by phil B

picon face
Minor correction. 10 mA * 1V = 10 mW    8 pins makes
for 80 mW.  Still not enough to worry about.

If you tie the LED high and light it by driving the
output low don't you get the higher differential
voltage (and thus the higher wattage)?  I chose to tie
low and drive high (no personal comments, please!).
the outputs were at around 4.5 V (iirc) so it was a
bit higher.  I use 5 for a conservative (and easier to
do in my head) number.  That works out to be a bit
less than 400 mW.  

Something that I wanted to look at but never got to
was to run the 595s at a lower Vcc to get output high
to be the LED voltage drop (lets say 2V for arguments
sake).  Then the max dissipation would be 2*8*10
(160mW) and eat less battery.

You will see more voltage drop with a higher current.
It wasn't too bad at 10mA as I recall.  I still don't
think drawing < 1/3 the max spec is abusive and my
experience reinforces that.  

Phil

--- Bob Ammerman <RemoveMErammermanTakeThisOuTspamspamverizon.net> wrote:
>
> {Original Message removed}

2005\05\27@122442 by Dwayne Reid

flavicon
face
At 08:44 AM 5/27/2005, phil B wrote:

>Something that I wanted to look at but never got to
>was to run the 595s at a lower Vcc to get output high
>to be the LED voltage drop (lets say 2V for arguments
>sake).  Then the max dissipation would be 2*8*10
>(160mW) and eat less battery.

I do something similar with that 40- LED board I described earlier.  All
the logic runs from a simple zener-regulated 5V supply but the LEDs anodes
are all connected to a Nat-Semi simple switcher set at 3.3V.  The LEDs
illuminate when driven LO by the hc595 and are reverse-biased with somewhat
less than 2 volts while off.  Well within the LED specs.

This display card is mounted to a piece of Lexan fitted to a cut opening in
an industrial control panel.  It makes for a completely water-tight and
fairly good-looking display but total dissipation was a concern.  Running
the LEDs at that low voltage kept the temperature rise very low.  Not using
a switcher would have resulted in considerable heat, given that the whole
thing is running from a 24Vac supply.

Note that the hc595s are running from the same 5V supply as the PIC - only
the LEDs are run at 3.3V.  Another advantage of doing it this way is that
the mosfets in the output stages of the hc595 are fully enhanced.  Running
the hc595 at 3.3V results in much higher RDSon and hotter chips.

dwayne

--
Dwayne Reid   <EraseMEdwaynerspamspamspamBeGoneplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 21 years of Engineering Innovation (1984 - 2005)
 .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-
    `-'   `-'   `-'   `-'   `-'   `-'   `-'   `-'   `-'
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.

More... (looser matching)
- Last day of these posts
- In 2005 , 2006 only
- Today
- New search...