Hi all,
I am looking for a very simple solution (if there is one) to 'pressing' power switch on a pc.
When voltage is applied to the circuit it changes a n/o wire pair to a n/c for approximately 1 second simulating a manual press of the pc front panel power button.

I would like to avoid using something like an Arduino etc.

Thanks all in advance
Richard.

 

Welcome to AAC!
Are you proposing to modify the PC by soldering to the PC power switch button?

 

Hi,
Thanks for getting back.

I'm looking to replace the 2 wire connector from the motherboard (maybe add 'inline' so I can keep the front panel switch).

All I need to do is to power up the PC from being fully shut down once the mains power has been switched on from the wall socket. I know the PC can be set up to reboot after power outage but this is not the scenario and the bios doesn't support power on from cold boot.

Thank you
Richard

 

When voltage is applied to the circuit

What supplies this voltage?

 

Can be a 5v /12v dc psu or 230v ac whatever is needed I have all available at the location. the 2 wires just need to be temporarily shorted. (simulate push button)

Thank you

 

A '555-based timer driving a reed relay might do the job.

 

Thanks,
I'll investigate this option (fairly new to electronics).
I will report back
Richard

 

Afternoon,
I have searched but cannot find a solution to your above suggestion. Could you recommend a circuit.

Thanking you in advance

 

A 5 V wall wart can power the timer circuit plus it's output small relay. You probably could figure out which wire is which, and if one of them is GND then you could drive the other one with an open-collector transistor circuit instead of a relay. If that is outside your skill set, there is nothing wrong with going with a small relay.

Separate from that, you probably want two timers.

A PC's power supply is actually two separate supplies, one for all of the power stuff, and a very small one to power the circuit that looks for the button press and wake up the big one. This is sometimes called the housekeeping supply. It is less than 5 watts, but still takes a small amount of time to wake up. A one-second delay is way longer than needed, but a nice round safe number.

So, power is applied, and after one second a small relay closes for one second to simulate the on/standby switch being pushed. Does this sound like what you are after?

If so, what is your skill set for building a small circuit? This could be a couple of transistors, or a couple of logic gates in a DIP package. I like two transistors over 555's; fewer parts.

ak

 

A 5 V wall wart can power the timer circuit plus it's output small relay. You probably could figure out which wire is which, and if one of them is GND then you could drive the other one with an open-collector transistor circuit instead of a relay. If that is outside your skill set, there is nothing wrong with going with a small relay.

Separate from that, you probably want two timers.

A PC's power supply is actually two separate supplies, one for all of the power stuff, and a very small one to power the circuit that looks for the button press and wake up the big one. This is sometimes called the housekeeping supply. It is less than 5 watts, but still takes a small amount of time to wake up. A one-second delay is way longer than needed, but a nice round safe number.

So, power is applied, and after one second a small relay closes for one second to simulate the on/standby switch being pushed. Does this sound like what you are after?

If so, what is your skill set for building a small circuit? This could be a couple of transistors, or a couple of logic gates in a DIP package.

ak

Hi, yes this is what I am looking for, I can solder but no good at designing or working out what is required. Simpler the better.
Thx
Richard

 

Can you measure the voltage across the push-button when not pressed?

 

Can you measure the voltage across the push-button when not pressed?

I cant check but my understanding is that it is no more that 5v

 

One transistor, 1 second timer with relay.

 

Hi, yes this is what I am looking for, I can solder but no good at designing or working out what is required. Simpler the better.
Thx
Richard

The 2 wires from what I understand is 5v into the switch then back onto the main board? It is a 5 volt logic signal, pull low to turn on.

 

One transistor, 1 second timer with relay.
View attachment 298024

Thanks for the reply, what would the RL1 relay be and how would it be powered, my electronics knowledge is tiny. Thank you.
Richard

 

One transistor, 1 second timer with relay.

That's where I was headed, but with a 2nd transistor in front to delay the relay operation.

ak

 

what would the RL1 relay be and how would it be powered,

The circuit and the relay are powered by a 5 V wall wart that has the same AC power source as the computer being controlled. The wall wart wakes up, powers the circuit, the transistor comes on, the relay contacts close, the RC delay times out, the transistor turns off, the relay contacts open.

R1, C1, and the transistor's operating characteristics set the amount of time the relay contacts are closed.

The relay can be just about anything. The contacts are switching only milliwatts of power, so a tiny reed relay would be fine.

Where are you located?

ak

 

The circuit and the relay are powered by a 5 V wall wart that has the same AC power source as the computer being controlled. The wall wart wakes up, powers the circuit, the transistor comes on, the relay contacts close, the RC delay times out, the transistor turns off, the relay contacts open.

R1, C1, and the transistor's operating characteristics set the amount of time the relay contacts are closed.

The relay can be just about anything. The contacts are switching only milliwatts of power, so a tiny reed relay would be fine.

Where are you located?

ak

I have gotten my head around it now, I will give this a try and give my feedback, just need to order the parts now.
You guys are great and quick to respond.

Thank you

 

That's where I was headed, but with a 2nd transistor in front to delay the relay operation.

ak

I'm thinking that no delay is necessary.
Just close the switch immediately and hold it long enough for the PC power to come up, and that would start the computer.
No?

 

I'm thinking that no delay is necessary.
Just close the switch immediately and hold it long enough for the PC power to come up, and that would start the computer.
No?

how would this be implemented with the above circuit