Arduino to power on computer

I have an old computer that doesn't have WOL. I would like to be able to wake it using another computer. I figure I can connect a transistor (base to pin 2, collector to ground) to the arduino and then the motherboard power switch (emiter and collector). Then control it by using pin 2. What am I missing. I have a bad feeling about this ;) .

My suggestion would be to look into using an optoisolator.

--Phil.

You could use a germinian diode.(sp) Which are like switches that are turned on when a magnet is near it. You could have this, and an electromagnet on the arduino...goood...luck

Germanium diodes [u]don't[/u] work that way. Okay maybe it might be possible to observe a Hall effect, but I've never heard of it.

A reed switch is more like it...it's a small glass tube with two contacts sealed inside, a magnetic field causes the contacts to stick together. If you use an electromagnet, you now have a reed relay. But you can simply buy those premade.

Okay maybe it might be possible to observe a Hall effect, but I’ve never heard of it.

The reason you have not heard of it is because it’s rubbish.

A hall effect device is a single piece of bulk silicon with electrodes at either end and across it. A diode is a junction of N and P silicon.

Is the on switch connected to the mains? If so be very careful and use opto isolation and an SCR or triac.

The reason you have not heard of it is because it's rubbish.

I was trying to give him a little credit. ;)

But some light Googling brings up the magnetodiode effect, discovered in 1958. This is caused by a Hall effect (a B field altering the path of moving electrons within a substance) inside the diode material. Obviously a diode specifically designed for this effect is going to be more useful as a magnetic field sensor than a normal diode.

Anyway, the effect exists, though it would useless if not unobservable with a plain germanium diode and coil as proposed.

Hey macegr thanks, I have never come across that one before, for those who are interested see:- http://books.google.co.uk/books?id=_H5n-5sO5BAC&pg=RA1-PA362&lpg=RA1-PA362&dq=magnetodiode+effect&source=web&ots=5viSYEfBz3&sig=S7rdy9SkCUfK3YBI4RUtQtRanIc&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PRA1-PA367,M1

:)

Excellent explanation of opto-isolators... which I agree with previous poster are things you ought to think hard about including in your circuit....

http://homepages.which.net/~paul.hills/SpeedControl/Optos.html

And if you want help with how the PC that DOES wake on LAN is going to "tell" the opto-isolator to tell the other one to wake up, see...

http://www.arunet.co.uk/tkboyd/ele1pp.htm