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Monday, August 30, 2010

USB Typewriter

USB Typewriter


Why make a usb typewriter?
There is something very magical about typing on those old-school manual typewriters. The weighty feel of the springloaded keys, the motor-car styling, and the beautiful marks they print on the page all make for a rich writing experience that can make writer's block melt away. However, the mighty hammering of typewriter keys has long since faded away, replaced by the dull click of the computer keyboard.

In this instructable, I'll help you bring your old typewriter back to life by converting it into a USB compatible input device for your PC or Mac! The hack is intended as a full keyboard replacement, so you can get rid of that piece of disposable plastic you call a keyboard and use the desk space for a classic, functional work of art -- A USB Typewriter!

What is so special about this idea?
Others have attempted this hack before, but while those implementations involved endless jumbles of wires, a disemboweled keyboard circuit, and a phalanx of momentary switches, this project involves none of those things and is actually quite simple and easy to implement. Not only that, but it will work on almost any manual typewriter. I have made quite a few of these USB Typewriters so far, which I sell on my etsy, and each one took 5-10 hours.

You can make one too!
I took the liberty of ordering circuit boards and kits for this project, which I made available on my etsy. If you are not a wiz with electronics, I would suggest you get the full kit here to make the assembly easier. However, if you are adventurous, it is entirely possible to wire up the circuitry shown in this instructable yourself, using perf-board -- Just look at the schematics in step 3. 

This project was created at Hive76, a rad maker co-op in Philadelphia PA. Visit them at

USB Typewriter

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step 1Overview (How it Works)

**NOTE: PCBs and Kits for this project are available here**

The Big Picture:

Under the hood of every typewriter (at least, every typewriter I've seen) is a springloaded crossbar that runs underneath all the keys. When a key is struck, part of that key pushes on the crossbar, and this causes the carriage to advance, the ink roll to move, and so on. We are going to repurpose this crossbar as a place to mount an array of metal contacts, which are attached to a long, narrow circuit board.  This Sensor Board is wired up to the Interface Board, an Arduino clone that talks to the computer over USB.

Take the time now to identify where the crossbar is on your typewriter -- just look for a bar that swings up and down when you press a key.

The Details:
The USB Typewriter 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 of metal contacts which clip easily underneath the keys of the typewriter. A number of shift registers allows the microcontroller to poll each of these contacts one at a time, so that 45 or so keys can be reduced to just 4 wires (a serial input, a clock, power, and ground). See the animation below for an illustration of how this works.

The USB Interface Board features an Atmega168P microcontroller chip (ie an Arduino chip), a USB Type B socket, and some supporting components (power supply, crystal oscillator, and USB voltage conversion). It controls the operation of the Sensor Board, and sends keystrokes to the host computer over USB.

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. Generally, I find that it is enough to install reed switch next to the shift key, the spacebar, and on the return carriage lever (to sense a "return" or "enter" command), although up to 8 reed switches can be placed near various keys in this way.  All reed switches run to inputs of the Arduino.

The Wires: Contrary to what you might expect, the USB Typewriter does not require much wiring. Only 9 individual wires must be run underneath the chassis of the typewriter, and an additional 2 wires must run out to the return carriage lever. This makes the USB Typewriter mod easy to install, and hard to break.
Overview (How it Works)
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