I would like to ask for help designing a circuit to turn on a relay when there is CANbus activity in a vehicle. (sounds like other questions but with CAN)
What I have so far is a SPST bistable latching relay (Hella 933364027) that I am driving with a ULN2803A darlington. One line to the relay turns it on (SET) , the other turns it off (RESET).
The RESET is already taken care of. But I would like help with the SET.
The darlington is wired so the SET signal needs to go to LOW for something like 10ms < 1s. But this should only happen when the relay is not closed (SET) already.
CANbus bus voltage levels are differential, 2.5 V +/-1.25. So what I looking for is a simple circuit that looks at CAN+/- and triggers the relay to go only pulling the SET line low long enough to activate the relay. The whole system is running at around 13-14v (automotive).
The more I think about it, this looks like a 555 of some such thing that looks for voltage on the differential CAN +/- and triggers for a short while but also has a disable line.
I appreciate any help here, and will certainly give credit in my article update (https://vinthewrench.substack.com/p/building-a-simple-safe-shutdown-switch)
How can I design a circuit that turns on a relay when there is activity on the can bus?