I want to sense a circuit state in an Automotive circuit (12V nominal) from a 3.3V microcontroller (MSP430Gxxxx). The circuit is normally 12V (or VBat) until either the Wireless ECU or a Door Key grounds the line, triggering an event. How can I safely (in terms of not frying the MCU or affecting the state of the line) sense this?
From the Manufacturer description, this seems to be a simple Open Collector system, it is not a power circuit, so I don't know how much current can be sourced.
I would tap into junction J6.
As this is automotive, current consumption is a concern as well. My MCU will be set up to interrupt on a falling edge trigger, and asleep unless that happens.