IBM Model F - Sensing PCB Thickness?

[ViviLazuli]

Hello everyone! I am new here and to mechanical keyboards as a hobby, but I have an electronics background.

I recently got my hands on a 122-key Model M that I am performing various mods on (I'll post the near-finished build relatively soon hopefully~). One of which is an M to F conversion. I do not know of a capacitive sensing PCB made for 122-key models, so I have used the published source files of idollar's (thank you!) FSSK/FEXT project for measurements to make my own in kicad. I am finished with pad layout and mapping the key matrix thus far

My question is, what is the thickness of the sensing PCB in the original Model F PCB or of the one in the FSSK/FEXT? I do not have one to measure so I would be glad if someone could help This is fairly important I imagine due to spacing within the capacitive sensor pads, as well as to allow the board to flex.

Thank you!

[kmnov2017]

0.8 mm will allow you to bend it in place to fit the curved backplate.

[ViviLazuli]

Thank you! I was thinking either 0.8mm or 0.6mm would be what I would want.

[sharktastica]

Welcome to the club! I look forward to seeing what you come up with!

[zzxx53]

I asked JLCPCB to build me some FEXT PCB (101 key) with 0.6mm thickness a while back, and they rejected my order saying that the possibility of warping is too high. I imagine that a 122 key version is even more problematic.
You might need to ask a few PCB manufacturers before finding one that will make it for you.

[ViviLazuli]

Thanks all for the advice and encouragement. I am still laying out the board but I hope to share the files here once it's a working prototype ^^;

Will report back once I find a PCB manufacturer that will accept it or after some rounds of revisions!

[anthonymak]

The one I am using is 7mm overall thickness (including solder mask and copper trace) When I order I said 8mm but turns our 7mm but it works perfect.

[ViviLazuli]

Thought I'd share some progress pics. Everything's routed, checked dimensions, and it just needs more polish (and maybe a little more design rules checking?) before I attempt to send out the order ^^

I also added some screen print art because a board this big felt like an empty canvas. I think it goes well with the column traces.

[cakeanalytics]

Love the artwork on the back!
Do you suppose you could put a few extra pads in the nav cluster area so that we could get the normal nav cluster layout?

[ViviLazuli]

Thank you!

Unfortunately, the 122-key board uses all 128 key matrix positions available on the xwhatsit controller (127 keys + one calibration pad, which may not be needed but I've never worked with a Model F before *shrug*). It could be done by removing pads under stabilizers for multi-wide keys, but that limits layout choices.

The solution I'm using is to convert the upper 5 keys of the cross-nav into a T-nav and using the bottom key for another purpose.

[ViviLazuli]

I also thought about putting a pad under the empty barrel to the left of the space bar, but alas.

[kmnov2017]

I also thought about putting a pad under the empty barrel to the left of the space bar, but alas.

Use this viewtopic.php?t=23406.

There are 24 pins for columns and 8 sense positions for rows on the PCB, that's more than enough keys you'll need (192 keys!).

[anthonymak]

Thought I'd share some progress pics. Everything's routed, checked dimensions, and it just needs more polish (and maybe a little more design rules checking?) before I attempt to send out the order ^^

I also added some screen print art because a board this big felt like an empty canvas. I think it goes well with the column traces.

Very nice one. but I wish that you can make 3.96mm instead of 2.54mm header pin pad.

[Redmaus]

Thought I'd share some progress pics. Everything's routed, checked dimensions, and it just needs more polish (and maybe a little more design rules checking?) before I attempt to send out the order ^^

I also added some screen print art because a board this big felt like an empty canvas. I think it goes well with the column traces.

Spoiler:

Beautiful! Looking forward to seeing your M122 brandished into an F!

[DMA]

As thin as you can get without getting into exorbitant prices per square inch.