My car has 3/4 doors with a motorised lock/unlock system with the driver's door being the only one without. That is how it came from the factory. Later I installed a remote lock/unlock system by retrofitting an electric actuator on the driver's side door. Thereby with the remote I could lock/unlock all 4 doors now. This works perfectly.
However, lately, I wanted to install a lock/unlock button inside the car, closer to the front passenger side. So that other passengers inside the can could easily unlock/lock the doors using this button.
The actuator I installed has two wires. It triggers lock/unlock by swapping polarity (12v) between these two wies.
The following is the wiring diagram from my existing remote lock/unlock system. Showing how to wire the type of door actuator I have. And it is how currently been wired.
I bought this button. It has two non-latching push buttons.
I developed this relay+diode combination circuit to connect the existing wire harness from the remote lock/unlock system. The red-circled circuit represents the remote lock/unlock system.
The red-circled circuit represents the remote lock/unlock system.
I had to use seperate set of relays, otherwise it would short both polarities to gether.
I have built the circuit on a prototype board and failed as the main 12v power rails fuse keeps blowing. when I press the buttons on the new switch, indicating a dead short or maybe 15Amp could not tolerate the current. No clue.
Does anyone have a better suggestion for what I'm trying to achieve? Or do you see anything that I'm doing wrong?
Ditch the additional relays and do the modification on the input side. I.e. build an interface that 'listens' for both the remote control and the two buttons you're adding, and then outputs the correct signals to the existing two relays. This prevents the situation where two signals compete, which is likely the reason why your present solution shorts 12V to GND all the time.
You could build this with a couple of logic ports, but at this day and age, it'll be more cost effective, more flexible and overall easier to use a microcontroller instead. Something like an Arduino Pro Micro is more than adequate and nice and compact to boot.
All you need is a simple Arduino/microcontroller board, a handful of resistors and a few transistors to drive the outputs in a 12V-safe way.
If you are going to hack into the vehicle electrics, I would have thought that you would want to get (somehow) at the point where either the driver's door switch or the remote control receiver detects and acts upon a lock/unlock attempt. How the actuators are wired seems not to be so relevant. If the existing driver's door switch is a momentary two position switch then you should be able to connect another similar switch in parallel without any other electronics. Or may be I am missing something.
Instead of relays, another alternative is an H-Bridge (often used for reversible DC motors) is an alternative to an array of relays.
