SPI Signal Ground

I have a long chain of 60 SPI controlled PCBs. Each PCB has a single ground connection, and can draw up to 330mA each. What’s the best method for connecting power and signal grounds to preserve the integrity of the SPI signals?

Right now I’m setting up a 14AWG (to support the ~19A total) main wire branch that each PCB will individually connect to. The question becomes how and where do I hook up the signal ground from the SPI controller (my Arduino UNO in this case)?

I’ve attached a simple schematic showing my current wiring plan, let me now what you guys think.

P.S. I’ve already verified with an oscilloscope that there are no signal reflections on the SPI line, so this is a ground problem not a transmission line/termination problem.

I would connect Arduino Gnd to the first board in the chain where SCK & MOSI go to.

Thanks, that's what I was also thinking. It's going to take me a long time to do the power wiring, but I'll let you guys know how it goes once I get it all back together.

Hi, can you show me your code. I am a beginer with the SPI interface, and Im using an SD Card module wich has its SS in pin 10, but I need to connect an ADC wich has MISO, MOSI , SCKL and SS. But Im not sure how to comunicate both in a simple code.

For the SD card, you need the Sdfat library which fat16lib has created & maintains.

ADC, need to know which one you are using.