Posted on Feb 6, 2014

It can detect what`s being typed on it. It can be used to send text to and/or receive text from a computer via USB. It was designed as a platform for playing interactive fiction games, in particular to play custom software being developed for it by Jim Munroe. As always, I hope to one day flesh this explanation out more, but since this is awork in progress, this will have to do for now. One important note,

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of which I am (unduly) proud: no permanent modifications have been made to the typewriter. This might be important if, in the future, I use a typewriter that I care about better preserving. Each key is attached by fishing line to a solenoid, an electromechanical device that pulls down when electric current is passed through it. 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 (integrated circuits that can, amongst other things, expand the number of outputs on a microcontroller). The shift registers are connected to an Arduino, which is connected to a computer via USB. When the computer sends a character to the Arduino, the Arduino chooses which solenoid to fire and sends that information to the shift registers. Detecting when a key is pressed uses a method very similar to that used by the USB Typewriter : a series of flattened resistors are placed such that when a typewriter key is pressed, the mechanism makes contact. The mechanism has been grounded to our electrical circuit to enable detection. Shift registers are used again here, this to to expand the number of inputs rather than the outputs. When the Arduino detects a contact, it sends the appropriate character to the computer via USB. It`s acting as...

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