This is the third installment of a series I am doing on modifying an IBM Model M. The plan and key layout is discussed
here. To sum it up the project so far, I started with an IBM 122 key terminal and cut off the numeric and directional keys to bring the total keyboard width to 15 inches which is about the same as the original IBM Space Saving Keyboard. You can read about that mod
here.
I’ve always liked on-key Caps Lock lights and have wanted this with my preferred key type – buckling spring. So while planning a bolt mod, I noticed that there is a stud under the Caps Lock key. This is true for all three of my 1391401 and my modified 1394100 terminal. I came up with the idea to drill this stud out, run a wire up the hole, and mount an LED there. But this would tie the back plate, membranes, and barrel plate together making disassembly difficult. I started looking up what was available in LEDs at Digi-Key and came across light pipes and surface mount LEDs. I bought several sizes and types of light pipes and LEDs to test. The
Bivar light pipes I ordered worked perfectly. I’m using two in this example - you might choose to use one, but order two or three for a few extra pennies.
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The surface mount LEDs that I ordered from Digi-Key might have worked, but were too small for me to solder leads to. Fortunately, I was able to find some pre-wired by
Miniatronics. My local hobby shop did not have them in stock, but they ordered them for me. They come with resistors, four to a package, in red, blue, or yellow. I ordered blue, so have three extra that I might give away or trade (anyone plan on doing red?).
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I used a .125” drill bit to drill out the stud. The 3mm Bivar light pipe fits snugly. I cut off the two micro-studs on the light pipe and used a drop of hot glue to set the LED. I added a 75 ohm resistor to the end of the red lead and extended both leads another 12 inches to the
Teensy. Thanks Soarer.
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The VLP-550-F light pipe protrudes 4.5mm out from the top of the barrel plate.
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If I had used a rounded top light pipe like the VLP-450-R there would be even more light spilling out from behind the key. I drilled a .125” hole in the top left corner of the Caps Lock key and glued another light pipe to the key to see how that looks. I like it best, but decide for yourself if you prefer back-lit or front-lit Caps Lock key indicator.
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These pictures were taken with a flash so the light appears less noticeable than it really is.
