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TV Typewriter replica project back on track

The thing that's throwing me is that the keytop design on the 'Honeywell' unit is *identical* to the MDS. And others as well.

This site shows a few keyboards, including a Burroughs unit. The keytops are identical on that one also in basic design, and the switches underneath are also identical. Has me wondering if they were all copying the same design or using the same subcontractor. I can see now why Don didn't give me a specific brand name.. all of these were 'surplus' from all over. But it would be interesting to know who ultimately made them.
 
As for the keyboard, take a look at the top of the switch with a button removed. If you see a "MICRO" molded into the top, you have your answer.
 
Did some more fine tuning. It has become clear that the keyboard Don used for his TVT, although ultimately made by Micro Switch like mine, was most likely from a Honeywell unit. The metal brackets on the side seem to be very similar. Nonetheless, I have been able to modify my keyboard (I got over that hangup) to match the layout. I had to countersink one side of it into the left side of the case, and then built a shelf on the other side for the other. That gives me the same width as Don's with the same arrangement. I also applied the vinyl to the wood and glued the case together. I glued on a printout of the switch layout on Don's just to get an idea of where I was headed. I've cut a hole under the vinyl for the rocker switches to go into. What it comes out looking like is fairly close, but I think my vinyl is slightly off color. I think Don's may have been some kind of tan or 'gold'ish color. What do you think? I found a company that makes vinyl dyes of any shade I want.. I might be able to re-dye and get closer. The wood sides.. I don't know... I'm hoping a decent stain might bring the colour closer to the original. The wood is not really looking much like Don's right now.

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Did some key painting.

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Unfortunately the key caps don't come apart. So the only way I can keep the top and callout separate is to fit a small piece of tin foil over the cap, paint the callout, then remove the foil. It's not perfect.. some tiny amounts of paint get under. Haven't figured out a way to make something to expose just the cap for painting.

The first row in Don's is all black, so I went that way:

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I then rounded up the blue keys to just paint the callouts. However to my horror on removing the foil cap from one of them and noticing a small amount of paint, in trying to wipe it away, the plastic was slightly melting. I don't get it.. the entire first row was totally painted over and it's fine, but this one wasn't. Don't know if maybe I have to wait more on the curing process. The paint is acrylic enamel spray I think.
 
Got the keyboard painted. I ended up having to hand paint the keytops blue, which wasn't too bad. I couldn't believe how well Ford blue engine paint matched the existing blue keys.

I also began lettering. I've no idea how Don did his. Looking at closeups on the museum site, it's obvious he cut them from something. Were they actual decals? Photocopies (think they had those in 73?). He made 40 of these keyboards. Must have been incredibly angst inducing.

For me, I cheated a little. I couldn't figure out how to match the font used and debated the merit and cost of having a printer help. Looking at Don's, it didn't look like his legends were glossy or anything fancy. So, I used a good photo of the original keyboard, scaled it, darkened it, and then printed on Avery label stock. Then just like Don, cut them individually. Toner incidentally isn't that great, although it does give a similar dull sheen to Don's. When you cut you have to be careful because the fibers of the paper break at the edges and the toner breaks away too. I ended up sticking the legends down and then going along the edges with a Sharpie. Amazingly.. it doesn't look that far off from Don's. Not sure what I'm going to do with the rocker switch labels and TV Typewriter front label. I *think* those might be thin metal. No idea how Don got those printed up.

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Well, if I had to do 40 of them, I'd have them screen-printed--cheap, easy and great for medium-sized runs. Most PCBs have component legends screen-printed. I think it was around in the time of the original TVT, since it originated during the Song Dynasty. You'll find lots of DIYs for screen printing on the web. Sometimes referred to as "silk screen"--but I don't think anyone uses real silk nowadays.
 
Ah yes.. forgot about screen printing. I tend to think of it being used for much bigger things. I could always go that route and just remove what I've done. I wish I knew exactly what kind of paper they would have used. I may have to go that route on the bigger labels, if that's the way to go. Hopefully they can figure out the font.

BTW are you sure about your dates? Pretty sure the TVT dates to before the Five Dynasties period.. ;)
 
Okay.. all done. Not bad I think. The paintjob on the keys themselves could have come out a little better, but it's tricky painting keys with two distinct parts like that when you cannot separate them.

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I have a mold setting for the square pieces that'll form the 'trim' around it as in the prototype. Those will be in place tomorrow. Really nowhere left to go for now but into PCBs. After consulting wood experts it was determined that the prototype sides are 'definitely' red oak. I also have an upholstery company in Great Britain with vinyl that looks pretty darn similar to Don's. They're sending me swatches by mail. I don't mind redoing the wood work and 'upholstery' one more time if it means I can get that much closer.

Going to PCBs, I am now just a single chip (7432 quad) shy of having all the ICs I require to move forward. I'm still vacillating on whether to try photosensitized PCBs or just do the laser method. I also have to figure out how to arrive at the correct scale for the PCB drawings, since measurements are absent (I guess they printed them at full size in the booklet, but I'm relying on Matt Holley's PDFs).

We talked about this before -- Signetics 2524 shift registers -- I found some TI 'SG2524' with date code 410... a) is that the right thing and b) can I assume that date code means 1974 10th week? Or is it possibly 1984? I was going through TI's date code reading info but the 3 digit codes in the guide don't line up with what's on the chips.
 
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Darn. So even my 1980 Signetics chips are wrong then. They are SG2524 also. I wonder how hard it's going to be to find legitimate 2524s out there. Haven't seen any without the SG ever. Thanks for clearing that up.
 
Well, I warned you at the start that some chips were going to be very hard to find. Check for the AMD chips that I cited a few posts back. You just might have some luck. The Apple I replicators have the same problem with finding the appropriate shift registers.

The golden age of MOS shift registers was about 1968-1976--when DRAM and SRAM came onto the scene it was pretty much over, aside from the analog audio bucket-brigade stuff.
 
Yes you warned me. :)

It looks to me like the 2524v is what I want, and it was used in a lot of military equipment. Maybe that was why it was hard to get even at the time?

I found a possible source here: https://octopart.com/2524v-signetics-6978522

I hate these giant component sites though. Most never answer their RFQs and very few actually ever have anything you're looking for. But this one shows inventory?! Unfortunately I can't order from there as they only deal with US customers, and while I have a US address, my Visa/MC is Canadian. But I wonder if they might actually have what I need.
 
I've finished making the 'surround' blocks for the keyboard. I'm very pleased with the end result.

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I think I'm coming around a bit, as a temporary measure to your suggestion Chuck about modern internals. I have a Raspberry Pi here that I've been playing with. I wonder how hard it'd be to get it to run a 'TVT simulator', and use my TVT's MDS keyboard. I'm still committed to building the boards per original specs, but I might use this thing a lot more if the Pi were an option.. make it simulate various vintage systems of the homebrew era (like a connection to a mainframe or SWTPC 6800 emulator, or even an Apple I emulator). Thoughts? Might make it a bit more useful.
 
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Well decoding a less-than 64 key keyboard like yours is pretty simple and an RPi is waaaaay overkill. If you only needed a serial output, then a very simple 8-bit MCU can do the job--you basically need 8 bits of output and 8 bits of input. Arrange the keys in an 8x8 matrix (or whatever fits), and have each key complete the circuit between an X- and a Y-line. Output a signal on the X-lines of the form 10000000, 01000000...00000001 over and over again to scan the keyboard, while reading the Y-line inputs. When you get a signal on the Y-line input, you know which key has been pressed. If you know what key was pressed before each scan go-round, you can also tell when a key has been released.

You can also implement this in TTL, if you want.
 
Found the shift registers (2524v). At least, allegedly. I called the Electronics Expediters and allegedly they have a bunch. I ordered 20 of them. Still deeply suspicious but we confirmed the 'v' at the end, shift register, made by Signetics. So we'll see what appears.
 
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