Teletype Model 43 Terminal keyboard

[OldIsNew]

I obtained a keyboard module from a Teletype Model 43 terminal:

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The switches weren't all working so I desoldered the PCB so I could remove and work on them. And the switches are what I think makes the board rather interesting. They are normally closed switches - opposite of most keyboard switches. And very clicky.

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The contact plates are normally closed and when the key is pressed a metal tab is pressed that flips back one of the plates and breaks the electrical contact.

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Some pics of the switch parts:

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Flipper Plate

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The loose end of the wire in the pic above is soldered to the second switch contact in the center of the pic below:

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Thankfully, after cleaning and reassembling the switches work.

I didn't want to desolder any ICs from the PCB because I think they just look too cool and I didn't want to permanently alter it.

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So instead, I decided to go ahead with a hand wiring job. I used female pin connectors instead of soldering directly to the switch terminals to make it easier to remove switches if they need to be worked on again.

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I altered the logic in my for Arduino C program to account for the normally closed switch matrix. All the rows and columns are kept set to HIGH at baseline then the row being scanned is temporarily dropped to low and the columns checked to see if they remain HIGH - meaning the key being checked is pressed (contact broken) - and thanks to diodes, it works! I'm glad I used the female pin connectors though, because several of the switches that I didn't open and clean - because they seemed to be working OK - are acting sticky and will have to be removed and cleaned.

working front2_sm.jpg (356.98 KiB) Viewed 2136 times

Quick video of typing on the board:

[Slom]

Nice one
I was very curious about the switches in these, so thanks.

[seebart]

Those switch rows remind me of Micro Switch Reed. Really nice, thanks for the video also!