As we speak, mechanical typewriters are out of date and we depend on computer systems for all of our writing wants. However there was a interval throughout the transition between the 2 during which electrical typewriters, then digital typewriters, and eventually digital phrase processors had been frequent. These phrase processors had been significantly attention-grabbing, as a result of they had been rather a lot like computer systems — they only had very restricted capabilities because of {hardware} meant to maintain prices down. Chad Boughton wished extra functionality from his classic Brother WP-2200 phrase processor and his first step was controlling the CRT with an ESP32.
The Brother WP-2200 was a digital phrase processor with a novel wide-format CRT (Cathode-Ray Tube) display screen. As a devoted phrase processor, it wasn’t actually a “laptop” within the regular sense, but it surely did have a floppy disk drive for loading and saving paperwork. However as a result of its solely function was to allow writing, it isn’t helpful for anything. Nonetheless, its kind issue — particularly that display screen — is actually cool and Boughton has concepts for utilizing it as one thing extra attention-grabbing than a phrase processor.
For this undertaking, he began the journey by carrying out two crucial duties: studying the keyboard matrix and controlling the CRT.
Studying the keyboard is definitely fairly easy, as just about all keyboards work in the identical manner. The important thing switches are wired in a matrix circuit, scanned row by row, which solely takes a handful of pins (equal to a minimum of the sq. root of the variety of keys). On this case, Boughton used a Teensy LC microcontroller improvement board to interface with the keyboard matrix and output the outcomes over serial.
Controlling a CRT is way more tough, because it requires exactly directing the electron beam with the deflection coils. These coils push the beam within the X and Y axes. Driving the coils requires calibration after which directing the beam in a helpful method, comparable to typical raster scanning, requires refined management.
As an alternative of controlling the CRT immediately, Boughton used a TTGO VGA32, which has an ESP32, to ship alerts to the WP-2200’s authentic CRT driver circuitry. These alerts are a bit like composite or VGA, however at a decrease degree and so Boughton needed to do some reverse-engineering with an oscilloscope to find out what enter the CRT driver expects. He was then in a position to output that utilizing 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 necessities of the CRT driver.
Now Boughton can learn key presses and management the CRT, which implies the Brother WP-2200 is prepared for no matter Boughton needs to do subsequent. He might, for instance, throw a single-board laptop in there and use the previous machine like a large laptop computer.
