Hooking into computer power switch that has a ribbon cable

[mlcampbe]

I would like to hook up an external button to power on my machine. I have read the threads that say to do so the easiest way is to just tap into the wires leading from the motherboard to the power switch. However, in my case the wires are a ribbon cable that has approx 10-12 wires in it. I can't see how that many are needed as the cable runs from the front power switch to the motherboard and the only thing on the front is power, reset, and a led.

What is the best/easiest way to tap into this type of wiring? Can I just remove the ribbon cable and something else?

How do I identify which pins on the motherboard are used by the switch?

[thecheat]

What brand of computer do you have? There is a standard that most manufacturers use when they make a board, then there are companies like Dell who do whatever they want since they build their own boards.

I had a heck of a time finding an example of a "standard" connector:


The power button would connect to the two light green pins on the bottom middle. If your pins don't look like that, all bets are off. You could start shorting adjoining pins with a screwdriver slowly, checking if it turns on. There shouldn't be any voltage there to be concerned about but YMMV. You can always backtrace the button leads to the ribbon cable with a meter.

[mlcampbe]

Well it is a DELL computer 

Looking closely I see there are 8 pairs of pins on the motherboard - 16 pins total and the only labelled ones are sleep and pwr on which appear to be 2 sets of pins each.

With this info I think I can start shorting pins but given there are 4 pins are there any gotcha's to look out for?

[mlcampbe]

I decided to do some testing - whats the worst that could happen, huh

I found that there is indeed a set of pins that turns the machine on and off. Now that I have this I just need to find a way to tap into those pins. What is the easiest way to connect 2 wires to these 2 pins without cutting apart the ribbon cable?

[Franco B]

I bought some JST connecters from dealextreme. There $2.98 for 10 with free shipping.

[Linky]

Huge pic alert!

[thecheat]

God bless DealExtreme - is there ANYTHING they don't have?

The JST plugs are probably the right size for those pins, too. You could always jump the button-end if you're keeping the computer in the case. I'm using a Dell laptop and am going to have to solder to the daughterboard to get my power switch wired.

[TAG]

I decided to do some testing - whats the worst that could happen, huh

I found that there is indeed a set of pins that turns the machine on and off. Now that I have this I just need to find a way to tap into those pins. What is the easiest way to connect 2 wires to these 2 pins without cutting apart the ribbon cable?

For the sake of those searching for a solution to similar issues down the line (and/or to save me the trouble of testing it myself when I get to that point  ), would you mind sharing which pins in your Dell did the trick?  Thanks!

[mlcampbe]

As I stated before the motherboard has 8 pair of pins as shown below below.  For example the set A1 forms a pair of pins.

The only pins that are labeled are numbers 3,4,5,6.

Pins 3 & 4 have "sleep" written under them and pins 5 & 6 have "pwr on"

A B C D E F G H
1 2 3 4 5 6 7 8

In my case shorting together the F6 pair of pins causes the computer to startup or shutdown (if kept shorted together for 5 seconds).

I hope that helps someone down the road.

[TAG]

I hope that helps someone down the road.

Thanks!

[severdhed]

another option would be to go to the other end of the cable where the actual PC power switch is...if it just has two wires going to it, tap into it there, if it is mounted on a PCB of some kind, then you would need to solder two wires onto the PCB where the power switch connects.

[Kevin Mullins]

And if need be you could follow the circuit traces coming off those two pins to the NEXT accessible solder point. Either on the motherboard side or the button side of the ribbon cable.
(maybe, without it in front of me it's hard to say what you'll run into)

[XeviouS]

In my case shorting together the F6 pair of pins causes the computer to startup or shutdown (if kept shorted together for 5 seconds).

Shouldn't the computer start shutting down instantly (instead of waiting 5 seconds) when you short out the pins if you have the shut down option set 

[severdhed]

the 5 second delay is not actually triggering the windows shutdown process, that just forces the power off.