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:

https://pac-audio.com/products/tr-4?_pos=2&_sid=b059f84a1&_ss=r

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

 

The problem with trying to do what you want is in the nature of a CAN bus pin. In the recessive state CAN_H will float in the neighborhood of ½Vcc. The exact value of this voltage depends on the transceivers connected to the CAN bus. In the dominant state, CAN_H will be actively held high by at least one transceiver on the bus. Again, this level may depend on the transceivers connected to the bus. IMHO I would advise using an actual transceiver to detect the presence of dominant bits and feed that signal to a retriggerable one-shot.

 

why would you want to trigger your dash cam from can bus? This seems a bad strategy to me.

 

Just monitor the Main-Batterie's Voltage.
It will jump-up over 13.8-Volts when the Engine is started.
This is a very reliable method.
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What vehicle? I know some of the newer trucks have a two position fuse for the 12V dash outlets. Put the fuse in one slot and the outlets are constantly powered... put in in the other slot and they will only be powered with the key on.