Trigger power to my Dashcam ignition wire based on vehicle Ignition from CAN high Pin on the j1939 port.

[markarupert]

I want to Trigger power to my Dashcam ignition wire based on vehicle Ignition from CAN high Pin on the j1939 port. I have attempted to use this module:

TR-4

Module senses voltages as low as 0.8v and provides a 12v output with a one second delay. It can be triggered off of speaker leads or 5v remote wires. Easily adds remote turn-on for aftermarket amplifiers Eliminates turn-on pop in aftermarket amplifiers

pac-audio.com

to detect voltage on the CAN high pin but the output voltage seems to bounce up and down. The Can pin seems to be between 2 - 3 volts and this device will sample as low as .8 volts. I am assuming that the Can pin must be floating down below that.

I am looking for another device that won't bounce. Maybe something thing that will continue to pass the voltage through for a couple seconds after the low voltage trigger occurs.

Any ideas

 

[Diver300]

That trigger module is not designed to look at a CAN signal. It's not certain but it might work better if connected to CAN-L.

CANbus has CAN-H and CAN-L, and the voltage between the two is near zero (recessive) and about 2 V (dominant). When there bus is recessive, both voltages are about 2.5 V, but that can vary a quite a bit and is not well defined, and CANbus ICs from different manufacturers will give different voltages.

When a vehicle is off, the bus will be in a recessive state.

CAN-L will be around 1.5 V when there is a dominant signal, which might be enough to trigger that TR-4 module.

To trigger the dashcam when the ignition is on, you should either detect more than 1 V between CAN-H and CAN-L, or detect more than about 13 V on the supply voltage. Either way, you need a time delay, but the TR-4 module has that.

 

[markarupert]

Forgive my rudimentary knowledge, I have worked with and around a lot of IOT and electronic devices but mostly programming. When you say "you should either detect more than 1 V between CAN-H and CAN-L" can I connect both pins going in to the trigger input of the TR4 or is doing that interfering with other device's data processing?