Each key is attached by fishing line to a solenoid. The solenoids sit behind and underneath the typewriter in a multi-layer structure. The solenoids are connected to a MOSFET, which allows the lower-power parts of the circuit to control the high-power solenoids.
The MOSFETs are connected in sets of eight to shift registers. The shift registers are connected to an Arduino, which is connected to a computer via USB.