Daisy chaining SMCs with USB


I’m trying to control two SMCs from one USB line and I’m having a lot of trouble. Could I have somebody lay out the correct wiring diagram for this configuration?



I find that there are several lovely illustrations about how to do the daisy chain but none of them seem to address how USB factors in, and the combinations I tried don’t seem to be doing it.

For the record, both SMCs are being run from the same lead-acid batteries, and each SMC works great when connected by USB to my PC. The software I’ve written uses the binary Pololu protocol to communicate, and I scan for daisy-chained devices by sending the Get Firmware Version once for each possible device number, and looking for responses. I have noticed that as I do this, the green RX LED on SMC2 does not indicate activity.


To connect to the Simple Motor Controllers’ serial ports via your computer’s USB, you should connect the boards according to the second diagram under the Daisy Chaining section of the controller’s user’s guide. In that diagram, from left to right would be the first controller (connected to the computer via USB) and then your second controller. (It sounds like your setup does not need a third device, unlike the diagram.) Both Simple Motor Controllers’ Input Modes must be “Serial/USB”. To use our example code, the Serial Modes must be “Binary”, and the CRC Modes must be set to “Disabled”.

If you are still having trouble after you have verified that you are using those settings, can you post a picture that clearly shows your connections? Also, can you verify that you set the two controllers to different device ID’s?


Thanks, Jon. Unfortunately I let the smoke out of one of my SMC since my first post. It was an unrelated situation–no daisy chaining involved. I was just going to use two separate USB connections to get around my daisy-chaining problem. It worked fine with my dev machine, but when I hooked up the Raspberry Pi to try it without a tether, poof. I realized too late that my Raspberry Pi and SMC’s grounds were 12V apart; I’d put the Pi’s power supply on the negative terminal of one of the 12V batteries, and the SMC’s ground on the other. Now the Pi’s I/O chip gets really hot and the SMC’s shows only the barest signs of life.

Any, thank you for the information. I’ll try your suggested arrangement when I’m back in action with two working SMCs.

Any chance you have a discounted replacement option for those of us deep in technical regret?


I am sorry that happened. I noticed that you have already contacted us through email about this specific issue; you should continue that discussion over email.