How to debug a CAN Bus

Projects Networking, Protocols, and Devices
1

I hope you can give me some suggestions how to debug a can bus problem.

I hope there are ways to see problems without a oscilloscope because that would be a bit expensive to buy.

To describe my concrete problem.
I set up a CAN Bus between two (also tried 3 successfully) arduino nanos and i used MCP2515 and MCP2551 with a 8MHz crystal.

I followed this tutorial to set it up on a breadboard. This article links to this page for the arduino programming. It is based on the seeedstudio library.

On the first day of me tries it worked without problems with 2 and 3 arduinos.
(even though i did not use any resistors to terminate the bus)

After this success I kept researching about other libraries which might be better than the one from seeedstudio or provide some more abstraction from the interface.

I found the CANBus library from Cory J Fowler, which seem to solve some bugs in older libraries.

But It did not work (I use for the interrupt pin 2) I also modified the receive and send example to a lower bit rate and to be clocked at 8MHz.

if(CAN0.begin(MCP_ANY, CAN_125KBPS, MCP_8MHZ) == CAN_OK) Serial.println("MCP2515 Initialized Successfully!");

(I also bought and added in between the termination resistors.)

I also let the loopback example run successfully

When i went back to the seeedstudio library it as well stopped working.

Because the library from Cory Fowler seems to be more up to date I think it does not make sense to try debug on this old library

The output from the CAN_send script:

Entering Configuration Mode Successful!
Setting Baudrate Successful!
MCP2515 Initialized Successfully!
Error Sending Message...
7
Error Sending Message...
7
Error Sending Message...
7
Error Sending Message...
6
Error Sending Message...
6

The output from the CAN_receive script:

Entering Configuration Mode Successful!
Setting Baudrate Successful!
MCP2515 Initialized Successfully!
MCP2515 Library Receive Example...

Any suggestions how to proceed?
Is there anything i can measure with a multi-meter?

2

I am still interested in ideas how to debug a can bus. even so my problem was caused by bad breadboard connections. For now I found the solution that it is helpful to duplicate the connections to the main power.

3

Debugging a CAN bus without an oscilloscope is limited in what you'll be able to determine. With a multimeter in resistance mode and the power removed from all devices on the CAN bus, you should be able to measure the resistance between CAN High and CAN Low at 60 ohms. This value is due to the two 120 ohm terminations in parallel.

With the multimeter in DC voltage mode and the BUS in an IDLE state, the CAN High and CAN Low lines should measure close to 2.5 volts in reference to ground.

It would be beneficial for you to have an oscilloscope or at the very least a commercial CAN adapter for your development.

4

you can have a look at Canbus monitor

also a USB-CAN dongle so you can monitor traffic on a PC is useful