PC Soft Power

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

I would like an Arduino to be able to turn a PC on or off - i.e short out the 2 pins on the motherboard which simulate a switch getting pushed in.

How can I achieve that? - has anyone else undertaken a similar project?

(i'm thinking of using web control with an ethernet shield)

Thanks,

Ian

2

The wire at the on/off key is generally pulled-up to 5V by a 4.7k resistor from the standby supply of the ATX power supply. You can pull it down by at least three methods, depending on your personal level of paranoia:

  • direct connection to ground and any digital output.
  • a transistor inbetween
  • an optocoupler inbetween
3

Or a simple +5vdc low current reed relay. The Arduino controls the relay coil through a digital output pin and the relay contacts are free to wire across any existing switch contacts.
Example: http://www.allelectronics.com/make-a-store/item/RLY-541/5VDC-SPST-N.O.-DIP-REED-RELAY/1.html

Lefty

4

So funny... generally I am the one who recommends reed relais. However they are US$ 2 ....

Just a correction... There is a voltage devider involved so the pull-up is not to 5 but to around 3 volts. But that makes not much difference..

5

Hi,

Thanks! - you dont know where there is a schematic for your idea do you deSilva?

Ian