the easy solution is to replace the momentary switch that came with the case with a latching one in the same form factor

post pic of the power switch and I'm sure we can help you find an appropriate one

Some "smart" AT-ATX converters may already incorporate the logic you suggest.

I have done a few latching conversions with E-Switch TL2285EE. It does work, but it doesn't spring back when it's in the "on" position which looks a little awkward. And you need a soldering iron and heat shrink--cut the wires to the existing power switch, solder them on to the appropriate pins, then heat shrink them to cover them.

You can also, of course, just short the power wires together, use the rear power switch, and leave the case power switch for decoration.

Well, I’m using a 386 AT motherboard mounted inside a Cooler Master horizontal ATX case. (you can see it in action in this video) For now, I’ve left the PSU on, and until I find a more elegant solution, I’ve placed a power strip with individual switches on my desk. I’ve labeled the switch for the AT PSU, so whenever I press it, the 386 springs to life and I just go back in time...

I finally got around to creating (IMHO) an elegant solution using a small 8-pin PIC12F675. Just connect your ATX power switch and a couple of PSU lines to the PIC, and now your ATX power switch works to power on/off your AT motherboard just like you expect. Pressing the power button powers on the PC instantly, but to power it off, you must press and hold the button for 1/2 second.

Here's the (nearly trivial) code if anyone is interested: https://github.com/timali/ATXPowerSwitch.

If anyone is interested in actually using this, you can buy a PIC for a couple bucks, or I have some spare PICs which are pre-programmed that I can send for the cost of shipping.

OMORES wrote on 2025-02-24, 22:41:

Well, I’m using a 386 AT motherboard mounted inside a Cooler Master horizontal ATX case. (you can see it in action in this video) For now, I’ve left the PSU on, and until I find a more elegant solution, I’ve placed a power strip with individual switches on my desk. I’ve labeled the switch for the AT PSU, so whenever I press it, the 386 springs to life and I just go back in time...

If you're still using the power strip for your 386, and if you would like to use an ATX power supply with the ATX power switch on the case instead, you might be interested in my solution (using a small PIC to adapt the ATX power supply and switch to an AT motherboard).

IHMO, the simplest circuit is using a TTL flip-flop IC. The green PS-ON is TTL compatible level, so every press on the power button invert its "Q" output. Can be mounted on a small prototype board and fixed near the case button. A 7474 can do the job.

Luzemario wrote on 2026-08-21, 21:38:

IHMO, the simplest circuit is using a TTL flip-flop IC. The green PS-ON is TTL compatible level, so every press on the power button invert its "Q" output. Can be mounted on a small prototype board and fixed near the case button. A 7474 can do the job.

Would that include debounce and ensuring after a power outage the state defaults to power off? Once I considered those the smallest PIC is so cheap it's easier to do that in software than add the proper components.

jakethompson1 wrote on 2026-08-22, 01:34:

Luzemario wrote on 2026-08-21, 21:38:

IHMO, the simplest circuit is using a TTL flip-flop IC. The green PS-ON is TTL compatible level, so every press on the power button invert its "Q" output. Can be mounted on a small prototype board and fixed near the case button. A 7474 can do the job.

Would that include debounce and ensuring after a power outage the state defaults to power off? Once I considered those the smallest PIC is so cheap it's easier to do that in software than add the proper components.

You can smooth out the debounce and reset using a few 100nF capacitors... microcontroller availability varies greatly around the world... here, even the most basic PIC isn't cheap enough and has to be imported, incurring a 100% tax. Sometimes, a simple 12F675 can cost up to 12 dollars... which, for me, ends up being equivalent to 69 dollars after conversion and government taxes.

Interesting. When I was looking into doing one of these in case I would ever want to buy a FLP01/FLP02 case and not immediately butcher the power switch, I ran into the fact that the PIC10F200 is 76 US cents here so it seemed hard to overcome that.