Detect ignition from OBD2?

[jgauthier]

Hey all,

I am working on a project that connects to a vehicles OBD2 connector. The project is in components, and I do not want all of the components to be active when the ignition/engine is off. (To not drain the battery)

I'm trying to determine if there is a reliable way to determine if the ignition is one, or the engine, just from the OBD2 connector. I have a few ideas, but I don't know who well they are baked.

1) The K-line and L-line on my two vehicles are 2.5v when the ignition is on. Perhaps I can use one/both of those as an "input".

2) I believe when the engine in on the battery voltage on pin 16 will be higher (maybe 13vs) than when it's not (maybe 12v). I could potentially use a voltage sensing circuit.

Any advice? Thanks!

 

[GreenGiant]

As far as I know the OBD II port is only active when the car is on, I know you cannot read anything with the car off. Therefor you would not need a sense circuit, just something that doesnt mind being powered on and off. It should be fairly easy to tie into the ignition circuit if there are always active pins on the port, most likely through the radio connections since it should be close.

Can you explain a little more what you are trying to do through the port?

 

[jgauthier]

Well, the project goal is to attach a device to the OBD2 connector and get data from it.
However, the amount of stuff I want to attach is too much for "always" on. so, I really want a trigger that can be used to go on and off. Only from the OBD2 port-- I want a single cable that is easy to move around my different vehicles.

 

[richengle]

Well, the project goal is to attach a device to the OBD2 connector and get data from it.
However, the amount of stuff I want to attach is too much for "always" on. so, I really want a trigger that can be used to go on and off. Only from the OBD2 port-- I want a single cable that is easy to move around my different vehicles.

DID YOU HAVE ANY LUCK WITH THIS PROJECT... IM TRYING SIMILIAR :]

 

[jgauthier]

Wow, this was a long time ago. Here's how I would approach this problem now. There isn't a signal, or anything else that goes "on" when you turn on the ignition. However, what does happen is the CAN bus becomes active. I would use the +12V signal to power a small, low powered, MCPU (like an STM32) (using a DC-DC adapter or regulator). Some stm32s have support for CAN bus on them and the ability to receive interrupts via CAN. If an interrupt comes in (a valid CAN signal perhaps). Once that signal is accepted do whatever else you want with that 12V signal. Boot something else, up or just use the STM32 completely. They are pretty awesome processors. Biggest issue right now is getting them.

I would probably use one of these on the CANH and CANL lines: ESDCAN01-2BLY.
I'd also consider using an isolated CAN transceiver.

Good luck with your project!