That’s a good instructable you’ve posted.
2 comments:
1.)
The HEF4794BP shift register can only SINK current, so you can’t just use 4 of them to drive the 8x8 RGB matrix. That’s why a source driver ( UDN2981A ) was used in the instructable to SOURCE current for the LEDs. Also multiplexing was used there, which works fine for just turning the LEDs on and off. The 74HC595 has tri-state outputs (0V, 5V, high resistance), whereas the HEF4794BP has open collector outputs (0V, high resistance).
2.)
If you plan to use PWM to get more than just 7 colors by turning the LEDs on/off “statically”, you should not use the UDN2981 chip! It is far too slow for that and you’ll get “ghost images” on the matrix. Been there, done that. That’s why the Rainbowduino uses a different source driver! It seems to be hard to get though, at least I couldn’t find a place that sells it.
You can see the >> negative smear effect << caused by the UDN2981 chip here at about t = 5s.