Trigger Remote WIth Arduino

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paintlax

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I have a car key fob with buttons for locking/unlocking the car. I was wondering what the best way to simulate the momentary switches being pressed using an arduino. I have a couple of NPN and PNP resistors but I am not sure how to wire everything up. I have a wire soldered to the trace (red) that is connected to the IC pin and another soldered to the ground (blue). When I touch the wires together it works. I tried connecting the red to the collector of the transistor and the blue to the emitter and then sending a HIGH signal from a pin on the arduino to the base but that doesn't work.
 

Do you know if the switch is high side or low side? Do you have schematics or pictures for the key fob?

Using a voltmeter you can determine which wire is the higher voltage. Also using the voltmeter you can determine the amount of current flowing through the switch. This will be needed later when you try to bias the the transistor.

If you use MOSFETs you can avoid biasing. BJT transistors like NPN and PNP are cheaper though.
 

you could use NPN or PNP as switches or using MOSFETS as switches to get your work done.. but the simplest is you buy 5V relays.. in India, they cost around Rs. 35.. they are cheap.. and very easy to use.. you could give them a try to..
 

Since the 'switch' works with one wire to ground, your IC has an active low input.

Therefore, an NPN transistor (collector to the IC pin, emitter to ground and the base to your arduino output thru' a resistor should simulate pressing that switch.
 

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