A dumb question, but I need to know.
I've got a car with central locking, the problem is I want to add 3 features to it using an arduino. I know that Pin 23 is the "LOCK" signal, and PIN "35" is the unlock signal.
I will be able to use an interrupt to determine 12V is present on one of the interrupt pins.
The document says that in 'Neutral' (i.e. no lock or unlock signal), there is 5V present on pins 23 and 35. When a signal is sent, it will be at 0V - so to get them to lock / unlock, I plan to join wires to the existing cabling at those pins, and then have arduino provide the ground source for it based on ignition signal.
What I don't know is how can I ground the pin using arduino to deliver the necessary 0V signal ? Is there anything I should watch out for in doing this - Am I right in joining on to the in place circuit (at the pin, there will be two wires leaving, one to arduino, one to the locks / switch - do I need to isolate that at all?
Some more info if it helps!: http://pdf.textfiles.com/manuals/AUTOMOBILE/NISSAN/Sentra/2003_Sentra/bl.pdf Page 17 of the PDF describes the involvement of the pins and the locks (5V neutral, 0V when key turned).
I plan to have the "ON" position of the ignition through a zener diode, and use that as an interrupt to indicate the ignition is on. When the ignition goes to "ON", a lock signal should be sent. When it goes to "Acc" or "OFF", an unlock signal should be sent (so a "CHANGE" interrupt should do it). I might then go further to have the key switch (detects key present in barrel), to then have a interrupt timed to send a lock signal.
Anything to watch out for with my plan?