An Ancient Brother Word Processor Gets ESP32 CRT Control

Today, mechanical typewriters are obsolete and we rely on computers for all of our writing needs. But there was a period during the transition between the two in which electric typewriters, then electronic typewriters, and finally electronic word processors were common. Those word processors were particularly interesting, because they were a lot like computers — they just had very limited capabilities as a result of hardware meant to keep costs down. Chad Boughton wanted more capability from his vintage Brother WP-2200 word processor and his first step was controlling the CRT with an ESP32.

The Brother WP-2200 was a digital word processor with a unique wide-format CRT (Cathode-Ray Tube) screen. As a dedicated word processor, it wasn’t really a “computer” in the usual sense, but it did have a floppy disk drive for loading and saving documents. But because its only purpose was to enable writing, it isn’t useful for anything else. However, its form factor — especially that screen — is really cool and Boughton has ideas for using it as something more interesting than a word processor.

For this project, he started the journey by accomplishing two very important tasks: reading the keyboard matrix and controlling the CRT.

Reading the keyboard is actually pretty straightforward, as virtually all keyboards work in the same way. The key switches are wired in a matrix circuit, scanned row by row, which only takes a handful of pins (equal to at least the square root of the number of keys). In this case, Boughton used a Teensy LC microcontroller development board to interface with the keyboard matrix and output the results over serial.

Controlling a CRT is much more difficult, as it requires precisely directing the electron beam with the deflection coils. Those coils push the beam in the X and Y axes. Driving the coils requires calibration and then directing the beam in a useful manner, such as typical raster scanning, requires sophisticated control.

Instead of controlling the CRT directly, Boughton used a TTGO VGA32, which has an ESP32, to send signals to the WP-2200’s original CRT driver circuitry. Those signals are a bit like composite or VGA, but at a lower level and so Boughton had to do some reverse-engineering with an oscilloscope to determine what input the CRT driver expects. He was then able to output that using the VGA’s TTL sync and analog video modified with a resistor ladder. The FabGL library helped him configure that output so it meets the requirements of the CRT driver.

Now Boughton can read key presses and control the CRT, which means the Brother WP-2200 is ready for whatever Boughton wants to do next. He could, for example, throw a single-board computer in there and use the old machine like a giant laptop.