Recycling an old cell phone to control a computer

I found this instructable: http://www.instructables.com/id/Power-On-Your-PC-using-your-Cell-Phone/
The instructable shows how to use the vibration signal to turn on the computer.
From my experience, the power button on the front of a computer can also be used to turn off the computer, so I think it would be possible to send an SMS to turn on the computer, and then later send another SMS to turn it off.

I am a total beginner when it comes to circuit design, but I do have experience soldering and replacing components on PCBs.

I need help with a few things:

1. From what I understand, the power button pins just need to be momentarily connected for the computer to turn on (when working on PC's in the past I have used a screwdriver to turn it on when testing). Would it be possible to build a circuit that doesn't need the 12V supply in the instructable? Since the phone would go in the PC case and charge from a USB header on the MOBO, I'd like to minimize the the circuit's complexity, but I wouldn't know how to adapt the circuit

2. I would like to do this right and use my own PCB, printed and etched at home, or if it will be too difficult, then perfboard. In any case, designing the circuit is the primary barrier for me.

Any help/advice/recommendations would be much appreciated.

No schematic at instructables.

I think you could build a 555 timer based circuit called a monostable vibrator to give you a one-shot output upon receiving a trigger signal from the phone. You may need to use the 555 output to trigger a MOSFET, which can act as a switch in parallel with your mechanical switch.

#12 said:

No schematic at instructables.

Click to expand...

The schematic was found on page 2 of the instructable:

wayneh said:

I think you could build a 555 timer based circuit called a monostable vibrator

Click to expand...

Thanks, wayneh. After reading up on vibrators and timers here, I think I understand the general idea.
However, I'm not sure what the difference is between the 555 monostable and a MOSFET Monostable, and which I should use. Which would you recommend?
Also, from all the one-shot monostable schematics I can find, it looks as though I will inevitably need a power source, and won't be able to address problem #1 in my first post - probably a silly request indicative of my inexperience with circuits. Would it be possible to power the circuit from the same 5V USB header on the MOBO that the phone will charge from? (MOBO has power off charge feature)
And finally, what will be the correct way of connecting the phone vibrator pins to the 555, or MOSFET monostable, depending on whichever is recommended?

Thanks a lot for the help!

Assuming the phone is charged, there should be no reason why you would need an external power supply.
Power button is self-powered, connect the circuit above in parallel to the power button.
I think introducing a separate 12v is a recipe for disaster, the switch is a contact switch.

Something like a sensitive reed switch would probably do.
In the past, I have played with extending the power switch outside the case. One day the switch got knocked off, leaving two wires unattatched. Waving a screwdriver near them was enough to turn the pc on.

To turn the PC off, don't you need to hold the power button for appx 5 sec?

Power on is press and release.

Power off is press and hold.

I think most motherboards has a feature in the BIOS regarding this.

This type of power off, doesn't turn off running programs. It only shuts down the PC. That could cause trouble when the PC is turned on again. Unless you have a program that closes all running programs....

nerdegutta said:

To turn the PC off, don't you need to hold the power button for appx 5 sec?

Power on is press and release.

Power off is press and hold.

I think most motherboards has a feature in the BIOS regarding this.

This type of power off, doesn't turn off running programs. It only shuts down the PC. That could cause trouble when the PC is turned on again. Unless you have a program that closes all running programs....

Click to expand...

It depends on the setting in the bios.
By default, most bioses are set:
Instant power on
Press-Hold 4 seconds, power off
Press-Hold 10 seconds forced power off (for the cases when the MB is non-functional).
It is possible to set the power button to be instant power-off as well.
Also, pressing the power button /should/ raise an ACPI power button event, which for most OS's should have a handler, which in most cases is start to shut-down. However, on Windows, anything like an open word-document would stop the shut-down.
On Linux, only failed file-handles should stop a shutdown.

coldpenguin said:

Assuming the phone is charged, there should be no reason why you would need an external power supply.
Power button is self-powered, connect the circuit above in parallel to the power button.
I think introducing a separate 12v is a recipe for disaster, the switch is a contact switch.

Click to expand...

Okay, good to know. As far as I had understood by my interpretation of the circuit above, the +12V at the top right meant there's a 12V power source. I guess it means something else, then?

coldpenguin said:

Something like a sensitive reed switch would probably do.
In the past, I have played with extending the power switch outside the case. One day the switch got knocked off, leaving two wires unattatched. Waving a screwdriver near them was enough to turn the pc on.

Click to expand...

Sounds interesting. How would the reed switch be attached to the phone vibration motor contacts and the PC power button contacts?

btw, thanks a lot for the helpful replies, gents. I'm really glad I joined.

Oh, before I forget: any ideas about the 555 vs. MOSFET questions from my previous post?

futureboy said:

Oh, before I forget: any ideas about the 555 vs. MOSFET questions ...

Click to expand...

Either can work and I do like the simplicity of the MOSFET idea. That will take a bit of experimentation to get the timing right and may not be terribly precise. Probably not an issue for your application. If you want something you test a bit and then hard wire in, the MOSFET circuit would be OK. If you want to learn more about timers and have more control, go with the 555. Note that the MOSFET circuit there will give an "off" pulse as opposed to an "on" pulse.