I am trying to use a transistor to switch a button on a remote control, by bypassing the remote control button for the collector and emitter of the transistor.

I am running a program on the pi to turn the button on and off every 0.5 secs, by turning on one of the GPIO pins every 0.5 secs. I know this program works, because if I connect the output pin to an LED it turns on and off spot on 0.5 secs.

But when I put that same pin onto the base of my transistor, it seems like the 0/low that I give out of the pin doesn't seem to register, either that or there is some sort of delay in the transistor switching off.

If I use the 0.5 sec for both on and off, the remote light just stays on permanently, until I kill the program (upon which after a few seconds the remote light flickers on/off about 6 or 7 times but much quicker than half a second. I have NO idea why this is happening!!)

I'm thinking of possibly putting a pull down resistor to try and help the 0/low output from the pin hit the transistor a little quicker and hopefully switch it off more instantly.

Does this sound right? Is there possibly something obvious I'm overlooking? I'm quite new to the electronics side of this.

I'm using a 2N3904 transistor.

I've tried putting a pull down resistor (made from the 3 resistors I have lying around, in series) but the values are only totalling about 250 ohms so it's not having the same effect as it would if I put, say, a 10K resistor in.

I've also tried switching the raspberry pi's own pull down resistor to on, with no effect (though I don't really know how to test if that's working or not)

  • You can find lots more help on the Electrical Engineering site on Stack Exchange.
    – Marla
    Jun 29, 2014 at 14:11

1 Answer 1


The remote circuit you are attempting to control should be a DC circuit. Notice on the schematic provided that the emitter of the transistor is on the more negative side of the remote circuit. Collector is on the more positive portion of the remote circuit. enter image description here

You should also be using a resistor in series with the base of your transistor. Using the internal Rpi pulldown resistor is ok.

Connecting to the remote circuit with collector and emitter reversed from what I have shown will not work well.

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