why does the scope signal drops to zero I connect 2 MCP2515 (via Uno) ?

Projects Networking, Protocols, and Devices
1

Hi, can anyone explain what might be causing this?

I'm running both arduino's and picoscope via USB's on my PC.

when powering just one board (the transmitter) the scope trace is exactly as i would expect based on the code but when I plug in the receiver board the scope trace flat lines to zero volts.

Running the serial print function through the receiver's Communication port I can see the message is being successfully transmitted but for some reason there appears to be equal and opposite differential voltage ?

The Can Bus is set up with 120ohm termination resistors and wired correctly.

Cheers

Jo

2

Does your setup have the same behaviour as the setup in this video?

If so then your system is working correctly.

3

jdeacon2:
Hi, can anyone explain what might be causing this?

You are posing a complex question with almost no supporting information. You have not even said what Arduino boards you are using, how things are powered or what the PicoScope is monitoring.

...R

4

Appreciate your feedback.

I'm using two arduino UNO boards which are connected via MCP2515 can bus driver boards.

Data captured on the serial monitor on both ECUs seems to indicate that the message was correctly transmitted and received.

The scope trace of the Can signal is also correct but I can only confirm this with the transmitter module not the entire system running. As soon as I connect the receiver module the can signal on the scope flat lines to 0V, but the output on the serial monitor of the receiver module appears to be reporting the correct values. So I believe the message is getting through but I can't explain why the scope signal drops when both arduino's are running.

Thought I'd ask the community here to see if anyone has experience the same issue because I've been scratching my head to find answers for some time but got no where.

thanks for your inputs.

5

I am not familiar with CANBUS and it was only the content of your Reply #3 that brought to my attention the fact that an MCP2515 is a CANBUS driver board.

I suspect it would make things much easier for anyone who does know about such things if you make a simple pencil drawing showing how you have everything connected and post a photo of the drawing. See this Simple Image Posting Guide

...R