USB Typewriter

Step 2 HOW IT WORKS

You don't really need to know how this works to perform the mod, but since you are probably as geeky as I am about this sort of thing, read on:

The Details:
The USB Typewriter system consists of three main components: the Sensor Board, the USB Interface Board, and the Reed Switches.

• The Sensor Board is a long strip of flexible metal contacts which clip easily underneath the keys of the typewriter. Each contact is attached to a different pin on a chain of shift registers, which act like a fireman's "bucket brigade", passing a signal down the line from one pin to the next (see the animated picture below).  When the signal being passed down the row of shift registers is intercepted by one of the keys the microcontroller is alerted to a keypress.
• The USB Interface Board features an Atmega168P microcontroller (i.e. an Arduino chip), a USB socket, and some supporting components. By sending the CLK and SER signals, it controls the operation of the Sensor Board (again, refer to the animation below), and by monitoring the "chassis" signal, it can detect keypresses. The animation shows that the Interface Board can tell which key has been pressed, based on which pin of the sensor board was active when the chassis signal was detected. The interface board also controls the USB jack that connects to your computer.
• The Reed Switches: Because the Sensor Board only detects keys that strike the crossbar, several important keys go undetected. These include Shift, Space, and Return. To deal with those keys, we use tiny switches that close when in the presence of a magnet.

The USB Typewriter is an open-source project!  Although you don't need them to follow these instructions, you can find all of the schematics and layout files HERE, and you can find all of the Arduino microcontroller software HERE.