It all started when I encountered that old white Brother AX-110 electronic typewriter. The daisy wheel was broken so I decided to crack it open and see what‘s inside.

Surprisingly, there was not much inside: Just a little circuit board with a microcontroller, two Mitsubishi M545 8-way darlington arrays to drive the stepper motors for the X/Y-axis and the daisy wheel, the keyboard and the mechanics. On the print head there was a very complicated mechanism with two small solenoids, a dc motor and a lot of gears. I figured it was used for three things ( they DID know how to save parts back then ):

1. 1.if none of the solenoids is activated and the motor turns clockwise, the spring for the hammer is pulled in position.
2. 2. if then the first solenoid is activated, the hammer is released and then again ready for step 1.
3. 3.if the first and the second solenoid is activated, the ink?( I think it‘s graphite ) cartridge gets pulled up, the correction tape is held in place, and the hammer starts hammering it histerically until both solenoids are deactivated and the motor has stopped.

I also found out that if you activate none of the solenoids and turn the motor counter-clockwise, the hammer is firmly pushed towards the drum. That‘s what I use for the Z-axis ( or pen-lifting-axis ).

I cut one of the darlington chips with the connectors out of the circuit board and mounted everything on a wooden plate, including the original power supply. I also added a little fan because the heatsink of the voltage regulator would get burning hot after a few minutes ( like 50°c ).

I also soldered connectors for the arduino out of some headers I got laying around.

later I added a reflective light sensor I built out of an led and an ir-resistor, which I use to detect the sides of the paper and also for scanning.