Connecting 5V arduino logic with 12V car logic I need to connect arduino to K-Line in my car's OBDII port.
I used an L7805 to power the atmega but how can I interface 12V car logic with 5V arduino logic?
The problem is, the connection has to be bidirectional- sometimes the arduino will pull the line high/low and sometimes the car will - the purpose of this connection is to get throttle, rpm etc. data.
This would be easy if the connection was one directional - I could use a transistor to steer 12V to going IN the K-Line and voltage divider if I wanted to do the reverse. But how to do both?
I found this that may be helpful to you.  this circuit allows for bidirectional communication between automotive K-line ECUs and an arduino.
 K-Line Interface circuit