PointLess LED Array

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PointLess LED Array

From Open Circuits

PointLess LED Array Project

Contents

1 Summary

2 What it Does

3 Parts List4 Circuit/Program Design

4.1 Circuit

4.2 Printed Circuit Board

4.3 Firmware5 Files

6 Building your own

7 Further reading

Summary

Name: PointLess LED Array

Status: still developing, but is working

Technology: PIC microcontroller with code in BoostC

Author: russ_hensel ( where you can find an email address to reach me )

Futulec http://www.futurlec.com/ sells an 8 by 8 array of 64 LED's in a package about 2 inches square. Butwhat to do with it. Well obviously light it up. That is the basis of this project. What is it good for? still lookingfor a good reason, but it was fun.

PIC microcontroller with code in BoostC.

Files now posted

What it Does

Displays designs on the array, you can spell out messages one character at a time or present little animateddesigns. The code supplied does all of these. Perhaps I will make a movie.

Parts List

PIC16F877A, my favorite, but I think it is time to move to the 18F series, just not quite there yet.

LED array I got the array from http://www.futurlec.com/ LEDM88OG. This is a two color array ( 64 leds ) , Iused only half of them, may use the rest later.

16 small signal transistors may not be necessary, but allow for larger drive currents

3 x 8 current limiting resistors

Substituting a couple of IC gets rid of most of these transistors and resistors. ( also fromhttp://www.futurlec.com/ )

For better parts list see the schematic.

tLess LED Array - Open Circuits http://www.opencircuits.com/PointLess_LED

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REG 5 volt regulator I used LM7805.

REL1...8 Current limiting emitter resistor say 200 ohm.IC2 Low side switch array ULN2803.

IC3 High side switch array UDN2891.

LED Array Not shown, go to futulec or other supplier and look around.

D1 Reverse protection diode, low current rectifier should work, as should just leaving it out ( works mostof the time, then the regulator blows, or not ).

Printed Circuit Board

There is still one air wire left, the rest all auto routes. ( I think the design rules... are in the eagle files, if notemail me. ) You can fix this with one jumper to the top side. ( or perhaps another way, you could even switchports and fix in software or the ribbon cable )

Firmware

I use several arrays to store the bits for any given display. The basic idea is to put the data for one column ina char then use 8 char's to display the whole array. We are basically scanning much like a television, ormultiplexing a set of 7 segment displays. The difference from a TV is that we put out the equivalent of awhole line at once.

I used a spreadsheet to help me visualize the display and construct the data for the array, see the filedownload.


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The code should be reasonably self explanatory. Send Questions to russ_hensel To make the circuit boardeasy to layout I have moved some bit and port positions around, you may have to adjust the software to makeit work with these changes

Files

All in one zip file, click here (http://home.comcast.net/~russ_hensel/OC/ledarray.zip)

This page. Format: Web Archive

Planning guide, shows resource/ pin assignment for PIC. Format: open officeCharacter bit pattern planning spreadsheet. Format: open office

Schematic and Board Layout Format: Eagle

Boostc source and other files, including HEX file. Format: BoostC...

Building your own

My project was hand wired and I made many mistakes. Despite this the code works and I have had a lot offun with it. Because I changed my mind on the right components and other details all the pieces might not gotogether for you without a little bit of jiggling. Some particular tips:

The circuit board does not show the array, just a ribbon connector. This goes to the array. One side to thecolumns, in order 1...8 the other to the rows. The ribbon connector is much bigger than needed, change it to

a smaller one.

The 877 is over kill a smaller PIC should work as well, since the firmware is in C it should be an easy move.Since timing is not critical you could dump the crystal if the PIC has a reasonable internal oscillator.

I used discrete transistors not the IC's shown, the IC's should work better, I think. ( and take up less space )

To make the layout work without crossing traces I reversed the connection order on the printed circuit low tohigh bit, you will have to reverse the bit order somewhere in the code as well.

The code is near ( or above ) the limit for the free BoostC compiler. Much of the stuff is in the effects data,you can delete some. There may also be a fair amount of dead code ( depends on where I am in developmentcycle ) delete this to reduce code size.

A higher clock frequency would give you more flexibility, lower may force in a flicker.

The value of the current limiting resistors is something you may want to mess with, make brighter, and/orburn out the LED's.

A 5 by 7 array could still do the full character set with some redesign of the fonts.

Use the spreadsheet for planning your own fonts and effects.

You may have a power supply that makes the on-board regulator unnecessary, but I would leave it in if youare running on batteries ( 9 volt transistor bat for example ).

The circuit is not very complicated, close to a development board. You could start from a development boardand put the other circuit components off board, perhaps on a board with the display. The hand wiring should

not be a big deal.

Things I am still working on:

Add some runtime selection of messages/display

Add lower case font.

Improve fonts.

Add PWM control of brightness.Add more display tricks to the software, perhaps some font variations.

There is most of the code in place for a real time clock, displaying time should be pretty easy

Other as time and ideas come to me.

Mistakes here? Please let me russ_hensel know.


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Further reading

Tobis Corner: RGB LED Matrix (http://tobiscorner.floery.net/projects/avr/rgb-led-matrix) also has an 8x8

array of LEDs. But it's much cooler, because each of Tobi's LEDs is a RGB LED, so it can display

practically any color.

Kevin Cuzner is making "Dot Matrix Clock" (http://cuznersoft.com/wordpress/?cat=13) , which uses

several 8x8 LED panels, each one apparently identical to this 8x8 LED array.LED

POV display

24" Wall ClockOptoelectronics#LED Arrays64 Pixels Roundup (http://interactive-matter.org/2009/05/64-pixels-roundup/) lists many interesting

things built out of a 8x8 LED matrix.

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PointLess LED Array