Burroughs B25 K2 - 3675 6104

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Master Kiibohd Hunter

13 Jan 2016, 22:51

Now that I've mostly recovered from CES, I can start posting keyboards again! I may not be able to post a keyboard every day, but I should be able to post one every few days.

So, this keyboard, I thought it was just another dome...turns out I was wrong. It's something very odd. It's a foam'n'foil dome very very similar to Topre, which I currently refer to as Prototopre as they appeared before Topre started making office equipment. My research currently points to Brother as being the most likely manufacturer/designer (there's a single Brother patent that references this dome design) but nothing concrete.

The strangest part about this keyboard though is that it's labeled as "Made in USA". All other Prototopre keyboards were made in Japan. The pcb looks extremely similar to the Japanese ones, so perhaps it was just mislabeled (or just a tax dodge :P). My guess is that it's from around 1984 or so.

These keyboards are similar to Topre in feel, but a bit less harsh. Unfortunately, many are in bad shape (this one is in amazing shape) with the foil pads falling off. (Fun fact, when I brought a Prototopre to the 2013 Toronto meetup, Ed Matias said he preferred them to Topre).

The keycaps on this keyboard are dye subliminated. I've broken sliders/keycaps on Prototopres before so I'm very hesitant to take them off.


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14 Jan 2016, 00:00

Is it possible to replace the foam and foil pad in these with a helical spring?

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Master Kiibohd Hunter

14 Jan 2016, 00:56

I've made the pads work even with my finger, so it might be possible. Though I'm not sure the thresholding is setup correctly.
My guess is that the pads are bare copper so the spring would have to be at least non-conductive.

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14 Jan 2016, 01:02

Bare copper? That's weird? Oo I thought an intrinsic property of capacitors is that the elements are separated by a dielectric. If you connect two capacitive plates directly they'll discharge immediately - unless that's somehow the objective here (but then it would just be the same as a conductive switch).

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[ XMIT ]

14 Jan 2016, 05:13

Turns out air is a really good dielectric.

I'm not sure these pads are actually conductive on the bottom. Hard to tell from the photo. Maybe they're a metal foil or mylar and thus conductive. Maybe they're covered with a thin insulating layer and thus not conductive.

Thanks HaaTa for the photos. I have a nearly identical board here that is labeled "Made in Japan". You mentioned that you got something to trigger with your finger - do you have a protocol converter for this one?! It would be neat to actually use it.

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[ XMIT ]

14 Jan 2016, 05:14

Oh, and - these key caps come off easily enough with a wire puller if you pull straight up (if they are the same as the one I have in the garage). It looks like a Topre mount except with only one nub at 6 o'clock instead of two at 6 and 12 o'clock.

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Master Kiibohd Hunter

14 Jan 2016, 05:55

So, I was going to make a protocol converter for one of my Seikosha keyboards (Epson).


But, I found that sent out ASCII rather than press/release signals so I moved on to another keyboard (this was around the time I was doing a protocol converter almost every week). The easiest test was trying out the capslock key because the led would turn on when I pressed it. Now, even the Model F is affected by your finger pressing the pad (it's basically a touch screen), it just depends on what the threshold is.

I have a few other keyboards with these switches that I'll be taking photos of pretty soon.

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14 Jan 2016, 08:27

Indeed. Capsense is indeed back in fashion after all these years. Model F and Topre PCBs will fire a key event based on just your finger pressing the sense pads. I haven't tried this on beamspring but I bet it works too. They could handle a hundred or so digital sensors at once back in the late 70s. Not quite enough for a touchscreen at the time, but getting there.


14 Jan 2016, 17:22

Thanks for sharing Haata.

The PCB design is just crazy complex.

I'm currently examining the PCB of an IBM PC-XT, a different style of capsense, and it's nowhere near as labyrinthine as that! Perhaps the IBM design uses a few tricks, such as the unconnected pad?

The IBM logic boards seem to have chips with model numbers specific to IBM, even those that are generic TTL, making reverse-engineering too cryptic for me. Is the Borroughs board populated with identifiable parts?

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Master Kiibohd Hunter

14 Jan 2016, 19:19

I think it may have identifiable parts, though there's more transistor logic going on in the board than what IBM did it seems. This particular board has a bunch of rework which is annoying when reverse engineering.

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19 Dec 2016, 19:37

I'm sorry to revive an old thread, but I feel this might be relevant, and perhaps it explains why your board doesn't say 'Made in Japan'? This one posted on Ebay (for an exorbitant price, especially considering how dirty it looks) has a simple black 'Made in Japan' sticker under the detailed label on the back.

http://www.ebay.ca/itm/Vintage-Computer ... Sw5ZBWOvZk

EDIT: I just noticed the top right 4 navigation keys are grey on this one, but it appears to be a slightly older version, as yours says 'Rev A' and this one just says 'Version 1'

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