RGB LED Matrix
What can you do with 100 common anode rgb leds? Build a 8×8 matrix and interface it!
The circuit uses 74HC595 shift registers with output latch. Each shiftregister interfaces one color + one shiftreg for the matrix rows. The interfaces uses 6 I/O lines for faster speed and easier interfacing. An AVR running at 8MHz can update the matrix with 8 brightness levels displaying nice fading colors patterns or colored text (or both). The sample program creates fading color patterns using a sine table. For smoother display a double buffer was implemented.
Download: rgbmatrix.c
July 9th, 2009 at 21:38
[...] RGB LED Matrix | Tobi’s Corner 13 May 2008 … What can you do with 100 common anode rgb leds? Build a 8×8 matrix and interface it! The circuit uses 74HC595 shift registers with output … tobiscorner.floery.net/…/avr/rgb-led…/123 – [...]
August 22nd, 2009 at 07:13
Great job! That’s the coolest display I’ve seen in a long time.
The 6 wire interface between the AVR I/O pins and the display is very clean.
Unlike the quirky interfaces with obscure exceptions that I’m often forced to use.
Because I am too often pin-limited in my systems, I would be tempted to use fewer pins:
* could eliminate the “row” pin by making the one-hot row select 74HC595 automatically select the next row whenever you finish loading data into the column bits, by wiring its SCK to the global RCK. But once the one-hot has been shifted out the end, it gets a bit tricky resetting it to the beginning — probably requiring more hardware.
* could use a 3 pin “daisy-chain spi”, with “data”, “SCK”, and “RCK” pins, by connecting the “data-in” of each shift register to the cascading “serial data out” of the previous 74HC595 in the daisy chain. But your method loads the 4 chips in 1/3 or 1/4 the time.
Because I like nice, straight, parallel lines rather than many-to-many crossing permutations,
I would be tempted to connect the LEDs as a “packed pixel” array.
The “packed pixel” array would connect the first 3 columns r,g,b to the first 3 pins of the first 74HC595 shift register, the second 3 columns r,g,b to the next 3 pins of that first shift register, and the third 3 columns r,g,b, to the last 2 pins of that first shift register and the first pin of the next register … but splitting that pixel across 2 chips probably makes the software more complex than your “bit plane” approach.
Years ago, some people would “brightness sort” their LEDs, putting the brightest LEDs at the top of the array and the dimmest LEDs at the bottom of the array.
Is that really necessary with modern LEDs?
November 3rd, 2009 at 06:53
have you ever tried sanding those LED for a better light diffusion?
nice work btw