Electronics How to boot from logical high signal

Hi,

I'm planning on using a remote doorbell to power my computer on.
I've got it and have it running from a molex. After stripping the unused parts I have a logical high signal when I press the button (4.5V, guess 100mA max)

The problem is, I don't exactly know how a power button works, I think you connect thee sense wire to the ground, but not sure

the easy way would be to use a relais, but I hate those clicking sounds

So, what would be the best way to hook this up to the mobo? A transistor? Optocoupler? Transistor used as a NOT-gate?

And could you please explain carefully, because my electronics are a bit rusty, I remember most components and their functions, but I'll make mistakes in the connections (for instance switch the C&E on a transistor or use a NPN instead of a PNP :s)

 

The easiest way might be to bury ther relay somewhere inside your pc, you would hardly hear anything. Otherwise, I think an optocoupler would work, with the led hooked up to your doorbell (with a resistor of course) and the collecter of the phototransistor hooked up to the sense wire, and the emitter to ground. An npn transistor would probably work, if you had the base connected to your doorbells output, the collector to the sense wire, and the emitter to ground. Just try what you have lying around, it is unlikely to break the on/off circuit on your mobo.

 

That's what I don't want to do, it might break, and it's cheaper to ask someone that knwos this kind of stuff (and I sure hope he reads this forum ) then to do it by trial and error and f*ck up my motherboard

 

You would need an inverter from the signal source to your mobo. This way, whenever the signal is low, the sense is held high; whenever the signal is high, the sense is held low.

If you want to isolate the remote doorbell's electronics from the computer's, use an optoisolator.

Read this for transistor operation on the inverter so that you may construct your own from scratch if you wish. The next page, although more complicated, is an interesting read that I recommend.

 

Something like this for an inverter ? (PNP trans, right ?)


only Q's that I have are :
-output to ground or sense pin on motherboard
-5V or 12V on inverter
-Isn't it bad for the motherboard to have a constant signal on that pin (if doorbell signal is low, the pin on the mobo gets a high signal)


optoisolator = optocoupler ???
if so, then it should be something like this ?


pin 1 being sense on motherboard and pin 0 being ground on moboheader


[edit]the problem isn't really the schematics, it's wondering how the power-button works

simple is output chip to Base of a PNP, E&C to mobo header, but what I remember from before is that in that state the mobo header will always recieve the 4.5-0.6=3.9V, and I'm wondering how healthy that is, I guess the best way should be the optocoupler instead of a relais

 

Nah, for that you'd want NPN.

Also, with an optocoupler (which is also known as a optoisolator), you'd want to put a 1k or so resistor in series with the LED.

The power button works by pulling a pin to ground, IIRC.

 

told you I would mix'em up

so, simple NPN (I know I can get a TIP31C in my local electronics shop) or optocoupler, what would you guys suggest

would it be necessary to isolate the 2 circuits ?

 

I would say an optocoupler, as they mean your mobo is completely safe.

 

I still got a mobo with 2 busted RAM slots laying around here somewhere, but it still powers on

I was going to use that to test if I could run it off +5VSB, wouldn't hurt to test the transistor there, but I'll probably go with the optocoupler

 

I'd second the optocoupler, and connect its transistor C & E straight across the switch, E on the low side. Seems safe whatever components are in line with the power switch. Must look one day.

A quick search found what looked promising here,

but he's chickened out and used a relay at the end of the line.

One slight worry about using a remote to turn the PC on is that a second, accidental, pulse will turn it off.

 

not really (in my case, not talking about DOS and Linux) I haven't set the power button action in my windows power management


that, and the doorbell I'm using can only send a signal once every 5 seconds, and my pc is at the windows logon screen in under 5 sec


only "problem" is, I can't hold the power button for 6sec to shutdown when the pc crashes, I'll have to pull the plug

 

Stick a manual switch somewheres, like the back.