Reproduce Circuit to Lock and Unlock my Vehicle Electronically

Thread Starter


Joined Nov 3, 2019
Hello Everyone,

I am attempting to reproduce a circuit in my 2005 BMW X3. I installed a remote start into my vehicle and the lock and unlock did not work with the remote start. So I am trying to reproduce the circuit that I can place into a small enclosure to pulse the lock and unlock to signal the general module to lock and unlock all the doors.

The circuit I am trying to reproduce uses two hall effect sensors (A3161E), I have attached the datasheet. I have also included an image of the circuit.


A simplified version is drawn below.


When idle the two hall effect sensors have a magnet over both of them. When the key turns clockwise to lock, one hall effect is uncovered and when turned counter clockwise the other hall effect sensor is uncovered.

I thought I could reproduce this circuit without hall effect sensors and just use two transistors, couple diodes, and relays if needed. I could use some advice if anyone here could help me make it so the negative (ground) trigger from the remote start will trigger either lock or unlock.

If there is more information I can provide that can help please let me know what I can find out for you.

I am trying to find an oscilloscope to see what is happening better and more visually but need to find one still.

The hall effect sensors are soldered onto the board in a two wire configuration so only a power/signal wire and ground wire are present for each hall effect sensor.

When I check the voltage of each power/signal wire I have 0.8 volts when plugged into the switch. When the wire is not attached to the switch there is about 9.0 volts at the wire. I tested each wire when the key was turned and the lowest the voltage dropped was to 0.730-0.750 volts. Wierd part is both lock and unlock wires voltage change. I dont know why this happens.

The remote start instructions adviced me that a negative signal would trigger the circuit to work. So I tried to just attach a negative ground to each lock and unlock but that did not work.

Thank you to anyone able to help me and I will try to help as much as possible.


Thread Starter


Joined Nov 3, 2019
Below are simplified drawings showing the magnet (seen in yellow) at different positions.

Rest Position:

Lock Position:

Unlock Position: