Electronics Question

[XcOM]

I have a quandry,

I am attempting to have two machines, with 3 power supplys, one will power all extras, Lights, Fans ect.

this will have a solid key switch so you can turn it on without the key, also with it being a solid switch i will just wire in the +5v and ground from the psu to get it to start.

The main bug bear i have is this, i want to use some sort of relay to make the switches on the other machines not work unless the main psu is turned on,

my first thought was to use a relay to complete a circuit so when you pressed it would complete it and instruct the machine to turn on, but for the life of me no matter how much i google i can't find an answer to this question,

of how would i do this, is there an easier option, or would a relay work.

if so is there anyone there who knows how to wire this up on a tech diagram, i am using software to create the wiring loom but this is the last bit i need to figure out.

Thanks,
XcOM,

PS, Renderman, if your electronics man could help, could you pm me his contact details.

[Xpirate]

Relays should work, but I'm not sure if they make momentary relay switches.

If all you want to do is prevent the other machines from powering on, the relays wired in series with the momentary switches would probably be the simplest thing to implement.

[XcOM]

good, thats what i wanted to hear,

now all i need to do is convince my bro.

[xmastree]

this will have a solid key switch so you can turn it on without the key,Not sure what you mean by that, but let's carry on...



The main bug bear i have is this, i want to use some sort of relay to make the switches on the other machines not work unless the main psu is turned on,I think I know what you're getting at here...

Two computers, each with their own PSU, and a third one running extras in both units. Neither PC will turn on unless the shared PSU is running.
Am I right so far? :?

That's easy. Use a 5V or 12V relay in each PC, energised from the shared PSU and route the computer's power buttons through a pair of NO contacts.

That way, if the shared one is off, pressing either power button on the PCs will have no effect.

[XcOM]

+rep both of you,

And yes xmastree, that was exactly what i mean, thanks for the advice.

[crazybillybob]

Make sure you put a diode across the Coil of each relay or the when the relay de-energizes it will spike the PSU and could cause it to shutdown (or damage it).
You make also need to "Debounce" the relay out put (this way the motherboards only see one push, not many) this maybe needed because relay contacts are on metal springs and when they closes the contacts actually bounce off one another causing multiple 0-5Vdc spikes, each spike could be seen as a button push.

A better way would be to use an Opto-isolator or a opto-couple (optical relay)
An Opto-isolator is a Transistor (semiconducting switch) that is triggered by an IR LED all in a small 6 pin package. With the little current needed to start the pc it should do fine. The switch would cause the LED in the package to light, which would cause the transistor to out put a voltage to trigger the Mobo to start.

An Opto-couple is an LED triggered Solid-sate relay (no contact bounce). The switch Triggers the LED, the LED causes the Relay to pass Voltage, the Motherboard starts.

Both are Triggered with + 5V and you'll not have to worry about the RF noise and Spikes that you see with a Relay.

If you want to go this way, Let me know I'll hook you up with Part #'s and a drawing on how to hook them up (It's pretty easy, just sounds hard ;) )

Good Luck!,
CrazyBillyBob

[xmastree]

You make also need to "Debounce" the relay out put (this way the motherboards only see one push, not many) Now you're frightening him...
For one thing, when the relay pulls in, there's no current through the contacts as the power switch will be in series with them. Current only flows when the power switch on the computer is pressed.
And I'll bet the power header on the mobo is debounced anyway.

[XcOM]

i was planning on using diodes anyway as i spoke to my dad about this, and he recommended both options, using a relay or billybobs version,. both would work, b ut he did say with a relay i would need to leave it a few seconds before i tried to turn on the other pc's to combat the debounce.

+reps both

[xmastree]

he did say with a relay i would need to leave it a few seconds before i tried to turn on the other pc's to combat the debounce. A few seconds? unlikely. milliseconds perhaps. By the time you have moved your hand from the main switch to the PC's power button, it should all have settled down.
Although, like CBB suggested, an optoisolator might be better.

[Xpirate]

Optical isolators would have a smaller foot print as well. They may be a little more expensive than relays though. You can find relays in junk yard cars. My old Volkswagen had several of them.

[xmastree]

Optical isolators would have a smaller foot print as well.

Slightly, but relays aren't always huge.

http://www.maplin.co.uk/Module.aspx?ModuleNo=37494&doy=25m9&C=SO&U=strat15

http://www.maplin.co.uk/Module.aspx?ModuleNo=2605


My old Volkswagen had several of them. yeah, automotive relays are much bigger, and unnecessary for this application.

[SXRguyinMA]

good info here, but I've got a related question...how can you hook up a PSU to get it to turn on without having a mobo attatched? like his 3rd PSU just to power lights, fans, etc. How do you turn it on without it bing hooked to a mobo?

[xmastree]

That's easy, link the green wire to one of the black ones.

[SXRguyinMA]

cool, I'll have to give that a shot, thanks! +rep