A little background for my project. I'm putting a small form factor PC into the shell of an old Gamecube shell. I would like the original buttons to perform their original uses.

The gamecube power button is a latching button and I need it to do two thing. First, I need it to momentarily power a relay that will connect the power button pins on the motherboard, this should only happen on the button press not when its pressed again turn it off (low to high not high to low). Second, the button also needs to control a second relay that will connect two pins on an auxiliary power supply that powers the GPU and its riser. The second relay can just turn on and off with the button. I have 5v power from a usb header on the motherboard, it is stand by power too, so it supplies 5v even when the PC is off.

Thanks in advance for any help.

 

First, I need it to momentarily power a relay that will connect the power button pins on the motherboard, this should only happen on the button press not when its pressed again turn it off (low to high not high to low).

Sorry, I don't understand what you want the button to do (or not do) when it is pressed again(?).

 

Forgive my crude schematic, but this what I'm going for, the box with the 'X' is what ever circuit is needed to turn on that relay for ~200 ms.

 

Sorry, I don't understand what you want the button to do (or not do) when it is pressed again(?).

While in the on (closed) position relay one should be powered and relay two should be briefly powered (~200 ms). While in the off (open) position both relays should not be powered.

I'm an ME student circuits are not my forte.

 

The gamecube power button is a latching button

What do you mean by this? Once pressed the button stay down? or is it just a regular momentary push button?

 

If the button is alternate action not momentary, the simple circuit below should do what you want;
The current through the relay coil (yellow trace) stays on for over 200ms after power is applied to the input (blue trace).
The pulse time is determined by the value of R1 and C1 (higher values give longer pulse).

 

What do you mean by this? Once pressed the button stay down? or is it just a regular momentary push button?

Left: Up/Off the two pins are not connected
Right: Down/On the pins are connected

 

If the button is alternate action not momentary, the simple circuit below should do what you want;
The current through the relay coil (yellow trace) stays on for over 200ms after power is applied to the input (blue trace).
The pulse time is determined by the value of R1 and C1 (higher values give longer pulse).

I'm not sure I understand your schematic, the switch is alternate action it functions like s spst toggle switch. I just want one relay to act like the switch was momentary and the other to act just like the switch. I'm intended to use (and have) two of these 5v relays G6DN-1A-L DC5 if that help or changes anything.

 

I just want one relay to act like the switch was momentary

Circuit in post #6 does just that, it gives a pulse of ~250ms

 

So my switch goes where the 'in' flag is?

 

So my switch goes where the 'in' flag is?

Yes

 

Yes

Like this? The +5 is a 2 pin header pin 1 is +5 and pin 2 is ground, PWR_Switch is a 2 pin header going to the switch pictured above.

 

Like this?

Yes.

 

I just noticed that the relay pulse time is actually only about 150ms, so C1 should be increased to 1μF or so, which will give a pulse width of a little more than 200ms.

 

I just noticed that the relay pulse time is actually only about 150ms, so C1 should be increased to 1μF or so, which will give a pulse width of a little more than 200ms.

Thank you for letting me know.

 

So, I made the circuit and it didn't work. It's almost definitely my fault. I changed the schematic from above to use what should be equivalent components, just through hole rather than smt. When I tested the circuit both relays cycled rapidly and repeatedly. I first thought that it was maybe because I used a polarized capacitor (is that a problem) but then I noticed that I missed the traces in my pcb design connected the coils of both relays (pictured below)

Left: error; Right: fix
Would that be the only issue with circuit? I'd love to not make a rev 4.

Thanks again for any help.