So I’m learning/playing around trying to set up a raspberry pi in my car (why not?)
I want the pi to shutdown correctly when the car turns off, so my plan is to take 2 12V inputs from the car, the “Always on” power (always connected to the battery) and the “ignition on” power (cigarette lighter circuit, when the car turns off, it goes to 0V).
I’m going to use a 78L05 to drop the 12V to 5V on both lines and feed the “always on” voltage to power a PIC.
The other 5V will go in to an input on the PIC.
When this input is LOW it will output a HIGH to the pi and that will get picked up and start a shutdown, also it will start a 3 minute timer then stop allowing 5V to the Pi (so I don’t start killing my car battery because it hasn’t shutdown)
When this input is HIGH I want the PIC to allow 5V (and enough amps to power the pi + charge a phone) to get to the pi…
I’m looking at relays and things I’m not really sure of the best/safest solution. Can anyone advise?
I’ve attached my crude photoshop control unit plan. with 2x 3 pin outs (5v/0v & shutdown signal) (I have rear seat entertainment so one Pi for each side!)
EDIT: I’ve just realised I need to provide 3.3V to the PI input. Any advice to simple drop that down would be appreciated also.
Car’s electrical systems are very hostile places; you often need a lot of filtering, overvoltage protection, reverse polarity protection, and the like when connecting to them. Look up “load dump” to see what you can regularly find there.
That sounds scary! I’d have thought modern cars with all their different ECUs and data networks would have one good protection circuit close to the battery and everything would sit behind that? It would make more sense (to me at least).
clocKwize:
… It would make more sense (to me at least).
I am a mechanic and through experience, what those damned engineers were/are thinking when they design vehicles is beyond me. If you have a scope, test the vehicle’s 12V port, it may be adequate. But, I would still filter/protect your circuit…
codlink:
I am a mechanic and through experience, what those damned engineers were/are thinking when they design vehicles is beyond me. If you have a scope, test the vehicle’s 12V port, it may be adequate. But, I would still filter/protect your circuit…
Haha, of course. Nothing is every as nice as you’d expect it to be when made by professionals. I’ll just use protection :shifty: Is that chip I linked to the right thing to do? Can you recommend anything?
