[Chris Gregg] had a dream. He wanted to convert use a typewriter as a printer. Sure this has been done before, but [Chris] wanted to create his own version. He picked up a 60’s era Smith Corona electric typewriter, with the hopes of driving its key switches with a computer. You can imagine his surprise when he discovered the keys were not electric switches at all, but a complex mechanical system which triggered a clutch to strike the actual paper. Realizing this was not going to be a simple wiring job, [Chris] set the project aside, where it remained for several years.
A conversation with [Bruce Molay], a coworker at Tufts University reignited [Chris’] interest in project. [Bruce] suggested using solenoids to press the keys. [Chris] dove in, and quickly had 48 solenoids on hand. The first problem was mounting the solenoids on the keys. [Chris’] roommate happens to be [Derek Seabury], president of Artisan’s Asylum Hackerspace. [Derek] created an acrylic frame which holds the solenoids and fits directly over the typewriter’s keyboard. This meant that no modifications needed to be made to the typewriter itself. Simply lift off the solenoid array and you’re ready to rock like it’s 1965.
The next step was driving all those solenoids. For that, Chris worked with [Kate Wasynczuk], one of his students at Tufts. [Chris] designed a board using Texas Instruments TPIC6A595 shift registers. The TIPC “power logic” series work like regular 74 series logic, but have seriously beefy outputs. These chips can handle up to 50 volts and 1.5 amps pulsed output current – plenty for [Chris’] 24 volt solenoids. [Chris] taught himself schematic entry and PCB layout in Eagle. After only two tries, he had a working board from OSHPark.
An Arduino Uno converts serial over USB output to a bit stream ready to clock into the shift registers. On the computer side, [Chris] wrote up a basic CUPS driver which allows him to print from his Macbook. The perfect demo for this project turned out to be musical. Click past the break to see The Smith Corona perform “The Typewriter Symphony”, by Leroy Anderson. This may be the first time this particular piece of music has been performed with actual words being typed, rather than random keys.