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Basically I've made a circuit of various LEDs passing through a single keyswitch. That means when I turn on the key, LEDs light up. I've connected a relay because the keyswitch I have, works opposite (when key if off, it passes current and vice versa). I'm using this circuit in my PC.

Now I've to pass power button and restart button from the keyswitch. I cannot directly connect it's terminal to the same relay, as it can cross trigger the power into restart and so on.

Should I need to connect separate individual relays to power and restart button in parallel with the 1St relay? Or there's are any other possibilities?

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  • \$\begingroup\$ What is it you're trying to do? Use the keyswitch to turn the PC on and/or reset it - or just enable the power and reset buttons? \$\endgroup\$
    – Finbarr
    Commented May 9, 2017 at 9:03
  • \$\begingroup\$ Just passing both the switches serially through the keyswitch. So that both the switches work only when the keyswitch is ON. In short enable the power and restart. \$\endgroup\$
    – fortyseven
    Commented May 9, 2017 at 9:06

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Yes, you could use three separate relays with the coils in parallel but there are better options. For starters, you could use a single relay with three contacts operated from the same coil, or two relays - one with one contact and one with two contacts.

However, the power and reset buttons on most of the PCs I've built have a common connection to ground, so you may be able to connect the two grounds from each button together and connect them to ground through a single relay contact. Here's a typical motherboard case/system connector by way of illustration, but you'll need to check your specific model to make sure this is possible:

enter image description here

If the LEDs run from the 5V supply, you may even be able to combine the LED ground and the button grounds and switch the whole lot to ground with the single relay contact you already have. If the LEDs run from 12V you can still do this, but you would need a diode to prevent them being powered from the difference between the 12V and 5V supplies. You should also check that the power and reset buttons are powered up together, as it's possible that one is powered from the standby rail and one from the main rail, again you may need to use diodes to ensure that they operate separately.

Finally, rather than use relay contacts you could use MOSFET or bipolar transistors as switches to turn on the LEDs and connect the button grounds.

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