Play A .WAV Instead Of Typing Line After Line Into Vintage Microcomputer

March 28, 2026 by Donald Papp 27 Comments

[Casey Bralla] got his hands on a Rockwell AIM 65 microcomputer, a fantastic example of vintage computing from the late 70s. It sports a full QWERTY keyboard, and a twenty character wide display complemented by a small thermal printer. The keyboard is remarkably comfortable, but doing software development on a one-line, twenty-character display is just not anyone’s idea of a good time. [Casey] made his own tools to let him write programs on his main PC, and transfer them easily to the AIM 65 instead.

A one-line, twenty-character wide display was a fantastic feature, but certainly lacking for development work.

Moving data wasn’t as straightforward in 1978 as it is today. While the Rockwell AIM 65 is a great machine, it has no disk drive and no filesystem. Programs can be written in assembler or BASIC (which had ROM support) but getting them into running memory where they could execute is not as simple as it is on modern machines. One can type a program in by hand, but no one wants to do that twice.

Fortunately the AIM 65 had a tape interface (two, actually) and could read and store data in an audio-encoded format. Rather than typing a program by hand, one could play an audio tape instead.

This is the angle [Casey]’s tools take, in the form of two Python programs: one for encoding into audio, and one for decoding. He can write a program on his main desktop, and encode it into a .wav file. To load the program, he sets up the AIM 65 then hits play on that same .wav file, sending the audio to the AIM 65 and essentially automating the process of typing it in. We’ve seen people emulate vintage tape drive hardware, but the approach of simply encoding text to and from .wav files is much more fitting in this case.

The audio encoding format Rockwell used for the AIM is very well-documented but no tools existed that [Casey] could find, so he made his own with the help of Anthropic’s Claude AI. The results were great, as Claude was able to read the documentation and, with [Casey]’s direction, generate working encoding and decoding tools that implemented the spec perfectly. It went so swimmingly he even went on to also make a two-pass assembler and source code formatter for the AIM, as well. With them, development is far friendlier.

Watch a demonstration in the video [Casey] made (embedded under the page break) that shows the encoded data being transferred at a screaming 300 baud, before being run on the AIM 65.

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Vintage Calculator Design Shows Just How Much We Take For Granted Today

February 20, 2021 by Donald Papp 14 Comments

[Amen]’s Rockwell 920 calculator from the 70s was a very impressive piece of hardware for its time. It sported a 16-digit display, a printer, and it could run programs. It even had a magnetic card reader/writer that could be used to store programs and data externally. Seen through today’s eyes, it was less like a calculator and more like what we would call a single-board computer. They are also a window into another era, a time when many of the electrical design assumptions we take for granted hadn’t happened yet. When the time came to dig into what made the calculator tick, [Amen] had a lot of work to do just to get basic tools running.

For example, [amen]’s Blue Pill (an open-source, multipurpose test and measurement tool) is, on one hand, the perfect tool to snoop on the inner workings. However, those inner workings happen to use negative logic at -17 Volts, which means a logical zero is -17 V and a one is 0 V. Oh, and it uses an oddball clock rate, to boot. Since the Blue Pill doesn’t support -17 V negative logic (does anything?) a bit of custom work was needed to craft an interface. Once that was working, the Blue Pill was off to the races.

The unfamiliar elements didn’t end there. The pins on each IC, for example, are in a staggered layout quite unlike the DIP pattern most of us (and our tools, breadboards, and IC clips) are familiar with. As for the processor itself, [amen] has access to low-level documentation on Rockwell processors and instruction sets, but the timing diagrams are puzzling until one realizes the processor has two clock inputs at two different frequencies, resulting in what [amen] describes as four separate “clock phases”.

These design decisions were certainly made for good reasons at the time, and they even have a certain internal harmony to them, but it’s still a window into an era when the elements underpinning much of what we now have and work with had not yet happened.

Check out the video embedded below to see [amen] explain what it took to hook the Blue Pill up to a Rockwell 920. Also, if you’d like to see one of these vintage machines demonstrated in all its functioning glory, here’s a video of one being put through its paces.

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