I need help making a circuit and then the circuit board

Thread Starter

TofuNinja

Joined May 11, 2017
6
I want to make a circuit board similar to this for a computer power supply.

https://www.sparkfun.com/products/12867

My issue is with the on-off switch. I want to be able to use the push switch that is on the front of a pc case to turn it on-off. Could I make a switch circuit that will turn the power supply on when I press the momentary button and then turn it off when the momentary button is pressed again?

I have never made a circuit board before so I don't know what I am doing and any help would be appreciated.
 

Dodgydave

Joined Jun 22, 2012
9,090
The atx psu is turned on by joining the Green wire to any Black wire, a simple 555 flipflop circuit with a push button will turn the psu on/off with one press.


FlipFlip.gif
 

philba

Joined Aug 17, 2017
960
Devil is in the details and getting your "specs" right. Are you saying you want to use a computer case for this with an existing switch? Or that you want to have a push button that simulates the behaviour of a PC on/off switch? If it's the latter, do you want to emulate the short press on/long press off behavior?
 

Thread Starter

TofuNinja

Joined May 11, 2017
6
Devil is in the details and getting your "specs" right. Are you saying you want to use a computer case for this with an existing switch? Or that you want to have a push button that simulates the behaviour of a PC on/off switch? If it's the latter, do you want to emulate the short press on/long press off behavior?
I would like to use the switch that is in the pc case. Is that button a momentary button like I thought?
 

LesJones

Joined Jan 8, 2017
2,609
You would need a latching circuit powered from the auxiliary +5 volts supply which is present when the main supply is off. You could use half of a CD4013 (Or almost any other flipflop) Wire it so it toggles on every transition of the clock signal. The clock signal would come from the push button. This would need a debounce circuit for reliable operation. You would also need a circuit to pulse the reset pin when power was first applied. I don't think a cmos chip would drive the power supplies power enable signal directly so would probably need a transistor or logic level mosfet.

Les
 
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Thread Starter

TofuNinja

Joined May 11, 2017
6
You would need a latching circuit powered from the auxiliary +5 volts supply which i present when the main supply is off. You could use half of a CD4013 (Or almost any other flipflop) Wire it so it toggles on every transition of the clock signal. The clock signal would come from the push button. This would need a debounce circuit for reliable operation. You would also need a circuit to pulse the reset pin when power was first applied. I don't think a cmos chip would drive the power supplies power enable signal directly so would probably need a transistor or logic level mosfet.

Les
About 9 months ago I tried to do this with a 555 circuit but couldn't get it to work. Do you have any links that you could share with examples of how to build the circuit you are talking about?
 

philba

Joined Aug 17, 2017
960
If you are using the switch in the case, there may already be a latching circuit. Pull the front off the case and look at the little board that the switch is connected to and test it. There will be several wires coming off it, one of which is the power on wire.

I think you could use the actual sparkfun kit - easier than designing your own and probably cheaper than sourcing the parts. That's still the case if you have to make your own latching circuit.

As to that 555 based circuit, it looks to be fairly sensitive to the values of R1 and R2. It is possible to get 2 10K resistors that don't make it work. I'd go with Les's approach. Pay attention to debouncing the switch - a simple low pass filter may be enough.
 
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