Peugeot 308: Control AC with Rotary Dials

Hello!
For many vehicles, the air conditioning system must be controlled via the touchscreen. This distracts the driver from the road and can be fiddly, especially on bumpy roads. For example, I would like to be able to adjust the air temperature without looking at the screen.

Therefore, I am working on building a module using an Arduino and 3 rotary encoders that will allow me to control the airflow and temperature on both sides with knobs. To do this, I will directly access the CAN-INFO-DIV bus, which has a speed of 125 kbps and is a low-speed bus. I have identified the corresponding IDs and data, but unfortunately, the CAN modules with the MCP2515 and MCP2551 only support high-speed mode. Therefore, I am looking for a module that supports low-speed mode or a way to convert the mode. Does anyone have any advice? Thank you in advance! Yule

Hello,

Nice project! What's the problem with the MCP2515? Why not just set it to 125 kbit/s? Or is there something special about the corresponding bus in the Peugeot?

Please also remember that the corresponding CAN ID can only be sent by one participant on the bus.

The typical approach is to have one side (transceiver) capture all CAN IDs and forward them to the other side (another transceiver), except for the ID that needs to be replaced. The CAN ID to be replaced is generated locally.

Best regards, Rainer.

Hello Rainer,
Thank you very much for your reply!
The problem is that the Peugeot and the Arduino are not communicating because while both operate at 125 kbps, the Peugeot uses the Low Speed Comfort Bus, whereas the Arduino can only send and receive data in High Speed mode.
According to this oscilloscope measurement, the recessive voltage for CAN High is 0 volts, while the dominant voltage is 4 volts. For CAN Low, the recessive voltage is 5 volts, and the dominant voltage is 1 volt.
So, I need to convert the frames from the Arduino to the low-speed version, and I don't know how to do that.
"It works perfectly with a Windows 11 tablet and a Peak Interface; apparently, this interface can switch modes. So there's no problem with the ID, etc.; the intended frames are okay."
Best regards,
Yule.

As a supplement, I'm including an oscilloscope image that shows what a frame generated by the Arduino CAN shield looks like.
Okay, these are not in the correct order. The one on top is an Arduino, and the one on the bottom is a genuine Peugeot part.

!! ISO 11898-3:2006 !!

That's the job of the CAN transceiver. You need to check what components are soldered onto your circuit board. For low-speed applications, for example, you might find a TJA1054A or a TJA1055T.

MCP2515 and MCP2551. According to the datasheet, the 2551 cannot be configured differently, and it does not have the corresponding pins.
I don't know if the 2515 actually offers the possibility of controlling another transceiver in a specific way.
The TJA1055T is only available as a surface-mount device (SMD), but it could potentially be used for that purpose.
I've been searching for a long time, but I haven't found a suitable part that can be connected via SPI.
Building a converter that changes the signal levels is conceivable, but exceeds my capabilities.
It's quite surprising that I seem to be the only one experiencing this problem. Hopefully, someone else will chime in.

Replace the MCP2551 with a suitable transceiver for low-speed CAN.
Just pay attention to the correct voltage levels; there's not much else to worry about besides CAN-H/L and RX/TX.

The examples I mentioned are just illustrative.

I have now found and ordered a suitable converter.
PCAN-TJA1054 (High-speed CAN to Low-speed CAN Converter).
Expensive, but easier than building something yourself. I received it in about 2 weeks and will report back here then.
In the meantime, I can take care of the code and the hardware.