TV Typewriter

I was an avid reader of Radio Electronics magazine. I don’t think I ever missed an issue. When the TV Typewriter article was published in September 1973, I had to have one. The magazine article was just the highlights of the design, so I sent off for the detailed construction package. When it arrived, I immediately began fabricating the boards with Radio Shack PCB blanks and a resist pen. I was too poor (or cheap) to purchase the ready-made boards. I also started scrounging parts. I managed to get nearly everything I needed from Poly Packs and Digi-Key, but I could not afford the MOS components (the 2524 and 2518 shift registers and the 2513 character generator), so I wound up begging my parents to buy the MOS chips for my Christmas. I placed the order with James Electronics (now Jameco) over the phone and my mom drove me to the other side of Belmont, CA to pick up the order.

In typical tightwad fashion, I fatefully decided to not order the male Molex connectors for the boards. I cut lengths of 14 AWG bare copper wire pieces (probably pulled from scraps of electrical cables) and soldered them to the board pads instead. Although it initially seemed to work, I later decided to tin them with solder. It would have helped if I had cleaned the flux off 🙄… The board stack would occasionally require a bit of flexing to re-seat the connectors when the unit would act up.

After the project was built, all it could do was to display characters I entered one at a time using a numeric keypad. Of course, I was too cheap to buy a real keyboard. Although I was pleased to have gotten the thing to work, I got the idea that I could possibly adapt it to be a poor man’s Teletype.

I managed to find an affordable keyboard. Back in 1974, that was quite a feat. I then designed and built a serial port and terminal add-on board using an AY-5-1013 UART and some glue logic to do the lower to upper-case translation and decoding the CR, LF, NUL, and BEL control characters. There was a DB-25 connector that provided TTL level communication at 110 or 300 baud. I also fabricated a metal enclosure for the whole thing at the high school.

I found a gutted acoustic coupler with no electronics. I designed a 300 baud modem from an Intersil 8038 for the FSK transmit and some Exar chip for the decoder. I now had the ability to connect with the high school district’s HP 2000E timeshare Basic computer. I could now “work from home.” At only 16 lines of 32 upper-case characters, it wasn’t great. But it was better than anyone else had at home at the time!

That acoustic coupler modem is all that remains of the TV Typewriter. There are no surviving schematics of the add-on board or the modem. Maybe one of these days, I will open up the modem and trace it out.