Vintage IBM: Big red switches!

[Guest_agentspikey95]

I thought this would be the ultimate beginner's PC mod, maybe i could try it on an ATX machine...

Remember how the old IBM PCs (and most other vintage IBM products) had those huge red flip switches on the back corner? I think iw would be awesome to add this to my dell optiplex.

So, is something like this possible on an ATX machine? anybody know where i can buy these switches?

[phreak97]

you could steal one from an old pc:P also, while, yes, it is possible, it's going to be hard to do with an atx machine.. actually, it might not be so hard. do you mind if the power button on the front of the pc does nothing? im not sure how stable its going to be, but theres a pair of wires you can cut from the motherboard plug and wire into the switch, this will turn things on and off, but i dont know if your pc will start up automatically when it's switched on.

[Agentspikey95]

Complete replacement is what i was aiming at.

What seemed fishy about it to me when I though about it, is an ATX power button makes contact only as long as you're pushing it, whereas an old XT switch (meant to supply power to the PSU, instead of trigger a signal voltage) make constant contact, which i assume would not work with ATX...

Everything should be pretty easy if i can get that to work. The power button, Reset, and HDD light are on a small PCB, so i can probably figure it's connector's pinout fairly easily.

Maybe even get to painting my computer tan, my drives back and replacing half of the front with a black grate (good idea for ventilation, more room for blue LED's  B)  

[phreak97]

well, i tested out my theory, and while it switches on the power source and gives everything power, the motherboard doesnt initialize, so it's useless.

[TJ_Kat]

or, instead of using an on-off switch from an old machine, find an (on)-off switch that looks just like it. It should retain the same functionality of the current switch while giving it the vintage look.

[kendrick]

The other option is to use the big red switch as an actuator for a separate circuit which activates a relay to duplicate the function of the OEM power switch. So even if the big red switch is a continuous contact switch, all it's doing is powering on a PIC or something similar which bounces a relay once and gives us our momentary switch action. Powering the switch off would duplicate the effect (for OEM switches that power the board both on and off) or would activate a different function.

-KKC, master of the overengineered circuit. It's like Rube Goldberg, but microscopic.

[Agentspikey95]

That's what i was thinking of doing, (only with a capaciitor- flip the switch, capacitor dumps it's voltage into a relay) but then that prvoides other problems I won't go into.

It all seems terribly coplicated...would it be possible to turn my PSU basically into an AT PSU, and wire it to be always on, then use the switch as intended, turning on and off the PSU's power feed?

It's gonna be hard to find one of these things aside from finding an old IBM at a thrift and stealing it's switch or case (which i'd rather not do, i'm a bit of a collector of those)
I know some older folks who cruise garage sales every weekend or used to work in the  computer business back then, maybe they know somewhere i can get a dead IBM PSU...

[viletim]

Agentspikey95,

Basicaly you want to use a DPST (standard AT) power switch in place of an (ATX) pushbutton...

The ATX power supply is turned on/off by connecting /PS-ON (pin14, green wire) to ground. It's (supposed to be) an open collector output from the motherboard so it's safe to do this while the mobo's plugged into it. Here's a couple of ways to do it with a switch.

1/ Connect /PS-ON to one leg of the switch and the + leg of an electro capacitor (say, ~100�) to the other. Connect the - leg to ground. When the switch is turned on, the cap will pull the line low and turn on/off the power. It will charge up in about half a second and the line will go high again. Probably a good idea to put a resistor (100k?) across the cap to bleed away the charge when off.

For this method, flipping the switch off and on again = 1 button push.

2/ Use a one-shot (logic gate) with positive and negative edge triggered inputs. 74LS221 is a good choice. Connect both inputs of the one-shot together and to Vcc via a pull-up resistor. These inputs go to one leg of the switch, the other goes to ground. Choose an R/C combination to give a delay of about a quater of a second. Connect the /Q output to the /PS-ON input of the power supply. What this circuit does is pulse the /PS-ON line low whenever there is a change in the input logic level. You might want to connect a diode in series with the output (annode to /PS-ON cathode to /Q) to fake an open collector output. Power comes from +5v standby.

For this method, flopping the switch once = 1 button push, which is what I think you were after. It's not quite ultimate beginner stuff though...

[phreak97]

only problem with that, is that turning on the power source doesnt start up the pc. it just switches all your drives and things on.
that's kinda what i was talking about before..

or did i misunderstand?

[viletim!]

whoops...you're right...
well...I can salvage most of what I said by replacing /PS-ON with the power input header on the motherboard. I don't think it's a good idea to send TTL logic into this input though. A 4066 (quad bilateral switch), a relay or possibly just a transistor (if the pin just needs to be shorted to ground) can act as a buffer between the circuit output and the motherboard. If using a relay then use a huge capacitor (for #1) or a transistor driver (for #2).