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Topic: Question about transistors (Read 503 times) previous topic - next topic

Rick S.

Hello fellow Arduino users!

I am working on a project that uses an IR sensor to detect a signal from a universal remote and turns on/off a computer.  One of my concerns is activating the power switch for the computer.  I want to retain the stock functionality of the power button, but also be able to electronically activate it.

So far, I have 2 2-pin headers connected pin for pin to each other.  one being where you plug in the case switch (just a momentary pushbutton), the other header will plug into the motherboard (probably with wires, not the header itself :) ), so when the case switch is pressed, it will connect the wires on the motherboard and voila, power!

Now, for using the arduino to connect the switch, I could use some type of relay, but that seems like overkill for such a small load (I can't imagine the motherboard uses much current to detect the power switch).  I think I can use a small signal transistor, but that would mean I would have to mind the direction that the circuit is plugged into the motherboard (because transistors can only flow current in one direction, if I'm not mistaken).  Here's a diagram:

My question: is there any way I can make a bi-directional solid state relay with basic components?  I have a bunch of transistors and diodes that will hopefully be able to do the trick.  thoughts?


Feb 12, 2009, 09:16 pm Last Edit: Feb 12, 2009, 09:16 pm by retrolefty Reason: 1
There probably is but I would always recommend the simplest, safest solution possible. Using a very small 5vdc relay like shown here can be driven directly from a digital output pin (use a fly-back diode across the coil if you wish) with no additional components required. The coil draws no more current then a standard LED does. The relay contacts allow complete isolation and are not polarity sensitive.



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