Home Automation Control with a 45-Year-Old ADM-3A Dumb Terminal

Basic computers today are so affordable that they’re almost trivial, as proven by the $5 Raspberry Pi Zero. But that wasn’t always the case. In the early days of digital computing, even the most attainable computers were quite expensive. In the ‘70s, many companies and universities had computers that easily cost tens of thousands of dollars. Those computers needed some sort of interface, and so relatively inexpensive terminals were sold to control them. Those terminals usually didn’t have any real processing power of their own, and only provided input and output capabilities. Daniel Karpantschof recently set up one of those terminals to control his home automation system.

The terminal that Karpantschof used for this project is a Lear Siegler ADM-3A, which was introduced in 1976. The ADM-3A was a “dumb terminal,” which means that it couldn’t do anything on its own. Its only purpose was to send text to an actual computer and to receive text back that was displayed on a 12” monochrome CRT screen. It cost $995 in 1976 (about $4,483 in today’s money), but that was far cheaper than a typical minicomputer from the era that could easily cost $20,000 ($90,000 today). It could communicate with a minicomputer via an RS-232 serial connection. It’s that connection that Karpantschof took advantage of for this project.

Karpantschof used a Retro WiFi SI RS-232 serial modem to connect the ADM-3A to his home network. The ADM-3A still couldn’t do anything on its own, but that modem lets it send and receive commands over the network. In order to accomplish something with those commands, Karpantschof configured a computer on the network that runs Ubuntu and has a bunch of home automation software installed. That software includes Google Assistant Relay, the Google Cloud Platform to gain the Google Assistant API, pyTado, the Console-Menu Library, OpenWeather.org API, and more. That Ubuntu computer is doing all of the work, and the ADM-3A terminal is simply acting as an interface for the front end. A command from the terminal could, for example, adjust an IoT thermostat via the Ubuntu computer. We think that’s a great use for a dumb terminal that is otherwise obsolete today.