K8055 use the board to power on & monitor computers


I’ve bought a velleman card (K8055) to be able to power on / off some computers from my network. Initially, I thought I would do it using relays. Though, the power on/off button on a computer is only a simple switch.

I would like to know if it would be safe to directly plug a digital output of the K8055 to the pwron plug of the computer’s motherboard (on/off to power on, and >4s to force power off) and monitor if a computer is running or not by connecting a digital input of the K8055 to the powrled of the motherboard.

If it is possible, may I do it directly or do I need to include any other component in between to avoid any problem (additional resistors for instance) ?

I think most safe solution is to use a relay. Look the K8055 manual page 22 how the relay coil should be connected. Connect the relay (normally open) contacts in parallel with the power switch of your PC.

Thank you for your quick answer.

I am going to see if I can find a relay corresponding to the task (input voltage of less than 5v in order not to add an additional external power supply to the system and low consumption).

For the other task (monitoring the running computers with the power led information), may I just include the input switch in series with the front panel led (from the computer case) to the digital input of the card ?

The voltage over the LED is too low for the digital input of the card. You may use the analog input to monitor the LED status.

I’ve done two circuits and both are working fine. To power on / off the computeur, I use the digital outputs with a +5v from the USB to power a reed relay which in turn is connected to the on / off jumper from the motherboard

To monitor the state of the computer I used a molex plug on which I connected another relay which in turn is connected to a digital input.

It’s working perfectly using the linux library and some small scripts.

It’s a bit like the WOL function but with the ability to reboot the computer remotely if it crashes :D.

This looks good and safe solution.
It is good idea to use the reed relays to totally isolate the systems.
Congratulations on your successful project!