64 pixel RGB LED Display - Another Arduino Clone

Step 3 Schematic

Image (1) shows how the shift registers are wired. They are daisy-chained, so data can be shifted into this chain and also through it. Therefore adding more shift registers is easy.

Image (2) shows the rest of the schematic with the MCU, connectors, quartz...

The attached PDF file contains the whole works, best for printing.

Comments

[kevindk92]

Hello,
what is the function of P1, P4 and P5?

(I love the project!)

[madworm]

P1: Connects to an USB/Serial adapter for code upload or control.
P4: Used for directly programming the chip (once for the bootloader).

P5: Some pins are shared between the programming port (P4) and the connections to the shift register chips. The jumpers can be used to disconnect them while using P4. You could also use it for connecting other things, but you'd lose control over the matrix of course.

[kevindk92]

thank you!

I've another question:
your last shift register IC5 needs to source over 200mA/port?
in step 2 of this instructable you said:
Each port can source or sink about 25mA of current. The total current per chip sinked or sourced should not exceed 70mA.
why aren't you using a ULN2803 instead?

(sorry for my bad english (Belgium))

[madworm]

Maybe 200mA peak, but the 1:8 multiplexing brings that down to about 25mA on average. Each row is only on for about 1ms. It is not ideal, but works. It's only a geek toy and not a professional LED display ;-)

I don't use an additional sink driver, because of chip count. If I had to rebuild the device, I'd replace the sinking 595 chips with tpic6c595 or similar and add p-channel mosfets to source current. I have a prototype with a source driver (udn2981a), but that chip is too slow for PWM.