Here's some more information on my
LED MATRIX

36x8 3mm Green leds. Using those complete 8x5 or 8x8 modules is like cheating... ;-)


The display consists of two parts, the LED/display board and the CPU/driver board.
The two boards are stacked together with *lots* of short cables... 


The CPU/driver board. Top row, left to right: 5 column drivers, intensity jumper, powersupply, data connector.
Bottom left to right: ULN row driver, RS232 Levelshifter, RTC, Text EEProm, Character EEProm,
PIC16F874, power connector.


Detail of the LED-module. See text for explanation.

Atlast I've built a working LED matrix project... =)
It took some time but it was woth every minute! 

LED Matrix Module
The module is built from two VERO-boards that is mounted with the tracks in different directions. First the leds was mounted on a black painted vero with the cathodes soldered to the horisontal cu-tracks. Then the remaining anodes was threaded thru another veroboard and soldered to the vertical tracks. This gives me a matrix with 8 cathodes and 36 anodes. Ofcource this isn't a good solution but as I like to use vero-boards in the most extreme ways I thought I'll give it a try...

CPU/Driver module
This module is quite simple. The CPU clocks row-data thru 5 Serial-in-Parallell-out shift and store registers. Then one of the rows is connected to ground by the ULN "driver" at the same time the CPU sends a "strobe" to the SIPO registers. Then the CPU sends data for the next row and so on. The data-stream to be shifted out is built up by the CPU by looking up text data in one EEProm and then resolv character/bit data in another EEProm. The EEProms (both text and chacterset) can be updated from a PC thru the RS232 interface. The current time can be inserted in the textdata by inserting a "Ctrl+T" character. Time is then read from a I2C RTC chip just before it is going to be displayed. The software is written in MPLAB assembler.

More information will probably follow here some time in the future...

>>>Thougths of Enhancements<<<
Things I'll do when I get the time...
A more simple solution for showing graphical images.
Temperature sensor(s)
Software selectable LED intensity.
A nice enclosure.
A new version with a doublesided PCB and SMD 2-color leds and IC's... =)


Technical information:
    Microcontroller: PIC16F874 @20Mhz
    Column Driver: 5x UCN5891A Serial-Input-Parallell-Output shift and store register
    Row Driver: ULN2803A (8 bit Darlington driver)
    Timekeeper: PCF8583  I2C Clock/Calendar
    Characterset Memory: 24C64 8k x8 I2C EEProm
    Text-data Memory: 24C64 8k x8 I2C EEProm
    LEDs: 256pcs 3mm Green Hi-Intensity
    Serial Interface to PC: 9600-N-8-1 Full access to both EEProms and RTC data
    Power: 5-12v @1A