I have a couple of AT systems in modern cases and one of the more annoying concessions is the power switch. Of course AT systems use a mechanical ON/OFF and modern cases have a momentary button. I have tried to search for a solution, but I think I don't have the terms right. Is there something that can bridge this; basically some electronic ON/OFF that can be triggered by a momentary?
You'll need an SPST switch and a DPDT (bistable) relay. It's a very common setup for things like rear fog lamps, or auxiliary high beams that interlock with the main high beams. It's complicated a little bit in that you probably are trying to control the 120VAC input to the AT power supply with it. It's doable but beyond my own desire to try to figure out exactly how to do it. (If you were doing this all on a 12VDC system it'd be a lot easier)
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Yello
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wrote:Would something like this do it?
No, because that's a latching, not momentary, switch.
Latching pushbutton switches usually have a detent where the button is outward and the circuit is open, or inward and the circuit is closed. Pressing the button will latch it inwards and will close the circuit and keep it closed until you press the button again and it pops out. A momentary switch is typically normally open (NO) and pressing it in will close the circuit *so long as you hold it down*.
It seems you want to press a momentary button once to change the state of the power supply from on to off and off to on, without the button itself latching into the on or off position. A momentary button only closes (or opens depending on if it's normally open (NO) or normally closed (NC); a latching button is either latched into the open or closed position. The goal is for the momentary switch to toggle the bistable relay from open to closed or closed to open.
Compare the action to the Turbo switch which latches inward and must be pressed again to unlatch, and the reset switch which returns to the original position as soon as you let go.
"The Big Bang. The ultimate hero of low frequency. The divine intergalactical bass drum connecting the tribes of our solar system."
Yello
"Solar Driftwood"
After some more research, it seems that what I am looking for is called a "soft latch circuit". But more to the subject of Vogons in general, I would have thought that making the momentary button on a modern case work to turn an AT motherboard on and off would have been a problem with a known solution.
Based on your post, I understand you want to use an AT motherboard in an ATX case. But what kind of power supply do you intend to use, AT or ATX w/adapter?
If you're using an AT power supply it generally comes with the latching button or rocker switch attached to it and you will have to find a way to somehow make it fit in your case. Keep in mind that you will have 120/230 VAC between the wires going in and out of that switch so you need one with the proper ratings.
If you plan on using an ATX power supply with an ATX --> AT adapter, you can replace the momentary button of your ATX case with a latching one of similar size (if you can find one). Then, you can wire the green and black cables of the adapter to it.
Here's a circuit to implement latching:
Cyrix Instead - Desktop Build
You'd use the Q output to drive a relay with a 5V coil and contacts rated for mains voltage.
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