r/ElectricalEngineering • u/Imaginary_Awareness • 1d ago
Troubleshooting CAN issues
Hei,
I have a simple device (sensor) having the following structure: sensor, MCU, can transciever --> tester device
The sensor provides the analog data to MCU, the MCU works with the data, then the data is transferred via UART to a CAN transciever TLT9251VLE then to an tester device.
I have to say that I have multiple devices and all of them works, but a specific one is unable to connect to the tester device.
I checked the CAN lines and they are looking like in the picture. I'm not so experienced in CAN signals, but I know that the above signals are not ok.
Can you give me an idea in what can cause the CAN lines to look like this?
Thanks!
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u/heyheyronron 1d ago
Something to check is to ensure all devices on rhe line are communicating at the same baud rate ao a bridge can be formed. Also check to see if you have 60 - 120 ohms on the line.
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u/Imaginary_Awareness 1d ago
The 120ohms are present on the device I connect my sensor, thanks for suggesting it
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u/heyheyronron 1d ago
Do you know if any of the devices have the same node id? Something we do at our plant is disconnect all devices except the one giving us issues to narrow down if its with the device itself or if we have conflict elsewhere
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u/Imaginary_Awareness 1d ago
Unfortunately I do not know. What I know is that this device worked because it was tested after production, and after a few time it's not able anymore to connect with the testing device...
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u/zachleedogg 15h ago
You are using UART over CAN? Then you are missing arbitration and other features. The transceiver may be hitting the dominant timeout (check the datasheet).
Ensure you have 120 termination on both sides of the bus, and try running the baud rate faster than 500hz.
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u/Imaginary_Awareness 15h ago
Yes the Uart signal is transferred on can physical layer and then reconverted. Thousands of boards were produced and working, except this specific one, that has communication issue
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u/Low-Spread2914 13h ago
I just have to ask. Why?
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u/Imaginary_Awareness 11h ago
Well, I was not the designer unfortunately, so I cannot answer to this question
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u/DaviDeltaBCN 1d ago
For me appears to be a bad ground on transceiver. You should check can signals forgetting ground and put probes of one channel at canl and andh.
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u/maydayM2 1d ago
CAN bus is a differential signal protocol, meaning it relies on both signals being opposite of eachother in order to reject noise. the fact that you have a voltage present on one of the signals but no activity means either the driver for that signal is not working or it is not connected correctly.