https://en.wikipedia.org/wiki/DIN_connector

7mm diameter

It's a DIN connector so you can probably find more specific technical drawings that show the exact size of the hole you need to punch, but these sizes have already been measured.

Ampera wrote:

https://en.wikipedia.org/wiki/DIN_connector

7mm diameter

It's a DIN connector so you can probably find more specific technical drawings that show the exact size of the hole you need to punch, but these sizes have already been measured.

PS/2 is 9.5mm in diameter.

XT/AT is 13.2mm in diameter - the pins are arranged in a 7mm diameter circle.

However, the hole size for the I/O plate is going to be bigger to allow for clearance as well as some variance in motherboards and motherboard trays, and the I/O plate mounting location.

I'm guessing that the I/O plate hole size is going to be around 16-18mm but would like an actual measurement from a mass produced I/O plate.

That's what happens when I'm on sleep deprivation

and am blind.

Ampera wrote:

That's what happens when I'm on sleep deprivation

and am blind.

I was wondering where you got 7mm from. I had to read through the Wiki page to find the 7mm figure.

I've done the same type of thing before 🤣

Just went and measured the one AT case I had handy at the moment. (It was a Full height tower from around the 486-Pentium era) This one had a circle that had two sides flatted on it. The diameter of the circle was 26mm (~1") and the width between the flats was 22mm (~0.9") -- If you take a 26mm circle and overlay a 22mm wide rectangle over it you'd get the shape of the opening.

Inset from the case and stood off closer to the motherboard was another opening for the keyboard connector, I couldn't quite measure it due to the depth but it appeared to be the same diameter as the width between the flats -- 22mm.

22mm would likely be a good hole size. You want it quite a bit bigger than just the diameter of the keyboard DIN connector as many of the keyboards from that era have a fairly large plastic moulding around the plug itself.

EDIT: I can probably also get you the measurement from my XT clone case over the weekend, see how it compares since I believe it is purely a circle.

chartreuse wrote:

Just went and measured the one AT case I had handy at the moment. (It was a Full height tower from around the 486-Pentium era) T […]
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Just went and measured the one AT case I had handy at the moment. (It was a Full height tower from around the 486-Pentium era) This one had a circle that had two sides flatted on it. The diameter of the circle was 26mm (~1") and the width between the flats was 22mm (~0.9") -- If you take a 26mm circle and overlay a 22mm wide rectangle over it you'd get the shape of the opening.

Inset from the case and stood off closer to the motherboard was another opening for the keyboard connector, I couldn't quite measure it due to the depth but it appeared to be the same diameter as the width between the flats -- 22mm.

22mm would likely be a good hole size. You want it quite a bit bigger than just the diameter of the keyboard DIN connector as many of the keyboards from that era have a fairly large plastic moulding around the plug itself.

EDIT: I can probably also get you the measurement from my XT clone case over the weekend, see how it compares since I believe it is purely a circle.

Thanks! The XT measurement would help as well.

On the AT case, in which orientation are the flat sides in regards to the motherboard?

The 2 motherboards I am looking at, the keyboard connector is 20mm wide, but measured diagonally, it is about 25mm. I guess 22mm would work, it would just have gaps on the sides.. and if somebody fumbled really badly it would allow them to scrape the edge of the motherboard with the keyboard connector.

I'm not sure it would need to be that wide as this would be for an ATX style case with a custom I/O shield that is a lot thinner than what the old XT and AT cases were. I'll have to make a mock-up to test with before I decide on a final size anyway.

Looking at a ps2/AT adapter and an XT? keyboard (doesn't work on my AT boards and I don't have an XT setup to test on), the max diameter is around 16-18mm.

For that AT style case the flats are parallel to the motherboard. Presumably the case was designed that way to give the biggest opening without getting too close to the side of the case.

About 5 minutes ago I made an I/O plate to use my 386 in a newer ATX case. I used a piece of a cereal box covered with aluminum foil tape on both sides, cut to size, with the keyboard cutout made specifically for the board. It is surprisingly rigid, and is fairly easy to to attach with a bit more aluminum foil tape and it even took a couple of screws through the case which will hold it a bit tighter. It looks way better than having nothing there (not to mention its far safer), it should provide EMI shielding due to the foil and it was super cheap (maybe 5 cents worth of tape) and required nothing but a sharp utility knife and some time. I'll post some pictures of the system in a build log soon. Its going to be interesting. 🤣

Well had to check the XT clone for you. It's not got a round keyboard hole, but instead has a rectangular slot of 40mm x 24mm. With the 40mm side being that parallel to the mainboard. The keyboard DIN sits just slightly off center on the long dimension. I don't think I have any more AT cases left to measure from.