CAN Bus Alarm System

Hello,

I am a software developer and I want to improve the technical aspects of my Citroen Jumper camper van in my free time.

An Arduino/CAN shield should listen for events like "door open" and potentially activate the horn and hazard lights/high beams, or possibly just an external siren. In other words, it's a CAN-bus based alarm system.

"However, in my opinion, this information doesn't seem to be transmitted through the OBDII connector (I'm currently testing with an Opel Adam). While several IDs are being sent, I can't identify an "origin" for them. All the IDs appear more than three times and seem to be only "responses" to the initial request."

I suspect, and I believe I may have read this somewhere, that these messages are received on the "Comfort" (slow speed) CAN bus and can only be accessed there.

Is that correct, and is that the CAN bus that can be accessed via the car radio connector?

Does only the engine CAN bus connect to the outside via the OBDII connector?

Regards,
Chris.

I'm not sure if this is the same for all Opel models, but in the ones I've worked on (Vectra C, Astra H/J), all three CAN buses are accessible via the OBD connector.

However, in this case, "comfort" refers to a mid-range speed, not a slow speed!

Pin 1 of the OBD connector is the Low-Speed CAN (33kbps), which is used for functions like the window lifter and other minor features. This is a single-wire CAN bus.
Pin 3/11 (+/-) is the MidSpeed CAN (95.2 kbps, also known as GMLAN), which handles functions such as climate control, radio, display, etc.
Pin 6/14 (+/-) is the High-Speed CAN (500 kbps) bus, which is used for communication with the engine control unit (ECU) and other devices.

The question is, where are you currently trying to eavesdrop ?

Apart from that, you probably won't be able to simply transfer what you're programming into Adam now to the Citroen!

Thank you for the detailed answer; it has helped me a lot .

I've been listening to channel 6/14 so far, but I'm going to try channel 3/11 now. I need the messages for remote lock and unlock, ignition on/off, and door open. I can't clearly identify those messages on channel 6/14. It would also be nice if I could activate the horn, turn signals, and high beams, but that's not essential.

The Adam system is currently just a proof of concept because the KaWa component is not yet available. The basic (software) architecture will be suitable, except for the specific CAN IDs and their corresponding messages.

Regards,
Chris.

Which CAN shield are you using, and which library?

From a library perspective, the 95.2 kbps might be problematic. In the library I use, I had to adjust the CNF values because the library did not natively support that bitrate .
I'm asking about the CAN-Shield because I suspect that the messages you need are more likely to be found on the single-wire CAN bus. However, to support that, you would need a CAN transceiver on the CAN-Shield that specifically supports single-wire CAN. The commonly used MCP2551/2562 chips on CAN-Shields do not officially support that.
I don't know if it might still work, but as a permanent solution, it might not be so great .

I also immediately noticed the reference to 95.2. It's currently the Seeed CAN-Bus Shield with the MCP2551/2515. There's a define called `CAN_95KBPS` – unfortunately, there's no `CAN_95K2BPS`. I'll try using it. If that doesn't work, I'll wait until the Citroen Jumper is available.

Thank you for your help!

Regards,
Chris.

I think 95 probably refers to 95.2.

Possible. Unfortunately, there are defines like CAN_31K25BPS and CAN_83K3BPS, which would suggest a CAN_95K2BPS.

You can check the values in the library.

These are mine, and they should work.

Code:

#define MCP_16MHz_95kBPS_CFG1 (0x03) #define MCP_16MHz_95kBPS_CFG2 (0xBB) #define MCP_16MHz_95kBPS_CFG3 (0x07)

There are different working values, i.e., if you have other values there, it doesn't necessarily mean that yours are wrong .

Deviations:

Code:

#define MCP_16MHz_95kBPS_CFG1 (0x03) #define MCP_16MHz_95kBPS_CFG2 (0xAD) #define MCP_16MHz_95kBPS_CFG3 (0x07)

How did you arrive at 0xBB?

I used a tool for that, it's called the "Microchip CAN Bit Timing Calculator."

Ah, ok. Datasheet sagt es gibt 3 CNF Bit Timing Register. Okay.

I will report back on whether it works...