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• from the start: software

  ch.dabre • 04/16/2014 at 11:14 • 0 comments

   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 )
  

• from the start : hardware

  ch.dabre • 04/16/2014 at 11:13 • 0 comments

  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.

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