04/16/2014 at 11:14 •
First, I did some little tests to get the pins of the stepper motors right ( I didnt find a datasheet on google ). I must add that I had never before worked with stepper motors and had no idea how to use them. Afer a little google search ( also about the darlington arrays and their function, I just heard that they were used to drive steppers ) I got them working and was drawing my first square on the drum plotter. Functions for penUp and penDown were quickly programmed, and after a lot of further programming and googling ( I‘ve tought myself the arduino language so far ) I drew my first 8x8 bitmap image stored in a simple 2d byte array. Using PROGMEM, I gradually increased that size up to 128x128 pixels, where the Arduino‘s storage was full. At that time, I was using an application I quickly wrote in Flash to get a png image to the arduino ( by copy-pasting the generated array definition into the arduino sketch ). But I wanted to go bigger and easier and so I looked into Processing, patched some examples of using PImage, reading pixels ,serial and controlP5 together and voilà, I had the perfect little printing software for my plotter ( one can almost call it a printer now, as it doesn‘t draw vectors anyway )
04/16/2014 at 11:13 •
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.if none of the solenoids is activated and the motor turns clockwise, the spring for the hammer is pulled in position.
- 2. if then the first solenoid is activated, the hammer is released and then again ready for step 1.
- 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.