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geekhack Community => Keyboards => Topic started by: ch_123 on Fri, 17 July 2009, 18:06:42
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(http://img197.imageshack.us/img197/9389/img3333a.jpg)
For those of you unfamiliar with it, it's a keyboard from the DEC VT100 (http://en.wikipedia.org/wiki/DEC_VT100), one of the better known video terminals. The keys are linear mechanical switches that feel very smooth. They're pretty light to type on except for certain keys, in particular the 'Set-up' and 'No Scroll' keys which are quite stiff, I assume this is to prevent accidental keypresses. I tried to take a picture of the switches, but it didnt come out well, I'll try tomorrow. Bascially - underneath the keycap are two exposed electrical contacts and a plastic border around them which the key stem slots into (as opposed to around it). Pressing on the key depresses the border which in turn causes the two contacts to move towards eachother until they meet in the center and make the circuit. Also, the Caps Lock is like those old Apple boards where it actually locks down when it's on. As for the connector, yes, it's the same as an amplifier jack. A friend of mine happened to have those adaptors that convert it to a standard mic jack. He then attempted to "record" the keyboard's output into a file while pressing the buttons, and then cat'd the file. But the file was just filled with zeroes. I guess this was because there isn't enough power from a headphone jack to power the keyboard.
The monitor part of the terminal was also there, and we tried to turn it on. When it powered up, it beeped (the speaker is on the underside of the keyboard) and the "online" status light came on, but nothing appeared on the screen. The terminal wasn't connected to anything. Does anyone know if this is normal? We thought it was odd because the bunch of us have played around with some of the later DEC terminals and something would still come up on screen, even if the terminal was disconnected.
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I believe the VT1xx series should be able to operate without anything connected to them. I will have to check out mine when I get a chance. I have a VT-101, basically a VT-100 without some of the more esoteric interfaces it could come with -20mA current loop, for example, which was a legacy interface for teletypes from the days of the ASR-33 Teletype, a common Teletype that was often pressed into service as a terminal because the early computers were able to use them as I/O devices. Long after the terminal became commonplace, the console typewriter, as it came to be called, was used as an operator's console because it produced a hard output useful for debugging problems and the like. I've got such a beast in my cellar; a DECWriter III. I'm not sure if it works or not, I haven't been able to coax output out of it. If it did, it would sure make a spiffy typewriter, provided I could convince it to be in full duplex with itself...
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Well, according to Kbdbabel, part of the jack is responsible for taking in current. I just havent been able to find out how much it needs.
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I'm currently downloading the VT100 Technical Manual (http://vt100.net/manx/details/1,4071) to see whether it provides any answers.
Oh, and seems like the board could use a good cleanup.
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Heh, yeah. The keycaps are really easy to remove, so I might yank them off and clean them off. Let's just say that it was found in a dusty corner of a dusty room.
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Page 4-37 seems to indicate that KB interface logic levels are 12 V and 0 V, so it seems like the board would need a +12 V supply. Apparently +5V is also present in the board (4-41).
Basically one would need to look at the circuit board. If some +5V fixed three-terminal regulator (typically some 7805) can be spotted, the case is clear.
That technical manual is interesting in any case, as it explains key scanning in some detail (see page 4-42, or 4-35 for the key matrix).
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:D cool find
ch_123, you are Keyboard Archaeologist of the Day!