Question about transistors

Forum 2005-2010 (read only) Hardware Interfacing
1

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 :slight_smile: ), 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?

2

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.

Lefty