A very long time ago, on take your child to work day, I went to my mom’s office. I got some stickers for something, then I traded them for this dumb terminal (they were award points for something at the office). This is an ADM3A, from 1977. It is all discreet logic chips, no major integrated circuits. This terminal is where the HJKL navigation keys in vi come from (vi was written on one and those keys have arrows on them on its keyboard). It’s also where the ~ = home directory in unix comes from as well, the ~ key is also the home key.
About 8 years ago, I thought it’d be a fun challenge to get this thing on the internet. I found an old laptop with a serial port, put linux on it, and configured it to use the serial port as a console. I ended up getting it online, and on IRC and Google Talk.
I found this terminal again recently, and wanted to get it back online so I could snag a pic of it on retro.hackaday.com. Unfortunately, it didn’t seem to work anymore. I took a look at it, and the part that failed turned out to be the big clunking mechanical power switch. It had gotten dirty and corroded. I took the switch apart and cleaned it out, and now it works again. Amazing for almost 37 year old electronics.
This time, however, I didn’t have a laptop with a serial port handy, so I made a MAX232 serial adapter for a raspberry pi and hooked the pi up to the terminal. The serial adapter is just a typical MAX232 circuit, I pulled it right out of the datasheet, page 7. You can get these things on ebay for a couple bucks, but I had a couple MAX232 lying around and I figured I could put a header for the pi right on the board, instead of having to make an adapter cable. I only bothered to hook up the tx and rx lines, I skipped DTR and CTR. I used a standard serial port header like motherboards used to have for the serial connection, so I could easily swap between 25 pin serial (which the adm3a has) and 9 pin serial. I had a bunch of the serial port header cables on hand as well….