0
\$\begingroup\$

I'm hooking up a microcontroller to be able to turn a bunch of computers on/off remotely. This is via the soft switch on the motherboard which doesn't carry any kind of load.

Looking at relays, the 5v one is slightly cheaper than the 12v one, both are 1A which is far overkill.

Does anyone know if I can save 5 cents by going with the 5v relay or do I have to splurge on the 12v ones?

\$\endgroup\$
  • 2
    \$\begingroup\$ You're mistaken, these 5V or 12V are the coil voltage. The allowed contact voltage usually is far higher. But it doesn't matter either, because the computer's power button is at 5V at max. \$\endgroup\$ – Janka Feb 19 '18 at 23:51
  • 1
    \$\begingroup\$ Which switch? Is it the the momentary button on the front? Is it the big clunky one on the back? \$\endgroup\$ – Nick Alexeev Feb 19 '18 at 23:53
  • 1
    \$\begingroup\$ Why wouldn't you use a magic packet on the network? .....much simpler if they have a network connection. \$\endgroup\$ – Jack Creasey Feb 19 '18 at 23:54
  • \$\begingroup\$ @jack Creasy Maybe OP wants the computers powered off completely. Mine for example can only be woken up from a power saving mode. user81993 You could simply measure the voltage to be sure. Google says 3.3V - 5V. Maybe this helps: electronics.stackexchange.com/q/129463/141308 \$\endgroup\$ – idkfa Feb 20 '18 at 0:12
  • 1
    \$\begingroup\$ @JackCreasey not an option if they crash and freeze up \$\endgroup\$ – user81993 Feb 20 '18 at 0:26
0
\$\begingroup\$

For, specifically, an "ATX" flavor power supply, every one I've looked at (and, I believe the standard they are built to) is a 5 volt logic signal, pull low to turn on.

However, it's certainly possible that some more modern than the junk I work with (after it's done computing, giving it a new purpose in life) might use 3.3 volt logic (most of the supplies I've got experience with do have a 3.3V output, but the power on signal is a 5 volt signal.) There seem to be MANY revisions of the standard, more than I care to sort through.

You might also want to make use of the "power good" logic signal, depending what you are doing.

You may not need a relay at all.

\$\endgroup\$
1
\$\begingroup\$

The current and voltage required for an ATX power supply to turn ON are tiny; connecting multiple computers GND together, and running it to another machine (your 'master' unit), however, can be problematic. Consider some inexpensive optoisolators (4N33, under $1) instead of relays.

Wiring in parallel with the front panel switch will make both the switch and your electronic control simultaneously effective.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.