I've bought two typewriters from a flee market. I thought of turning them into plotters. The first one had a stepper motor for the horizontal movements, but it feels the steps of the motor makes a rather big step, probably a half character step. And the cylinder also moves in large steps, probably with a solenoid. I might end up just disassembling it picking away motors and solenoids. It costed 1 €.
Then I found a 5 € Brother typewriter. Its cylinder moves very smoothly with small steps, maybe 10 steps per line height. Clearly a stepper motor, not a solenoid. And the horizontal movement is some 7-8 steps per character width. This typewriter will be my plotter project! Either I just use the original stepper drivers or I connect new drivers and spare me from the tedious task of figuring out pins and voltages and whatnot. The pen will probably be a thick-ish felt tip pen attached to the typewriter carriage. The solenoid that stroke the type wheel might do the pen down action if I can lower its force somehow.
Way back in the early 1980's, I was a communications consultant for a small company that put mini-computers in banks to do their processing. I looked at the Brothers typewriters to print output from computer terminals. A company produced a kit to add a serial interface to the typewriter. Worked very well. All the paper and print head movements were controllable, just as you found.
I have no clue if there is any documentation on-line for the interface.
That's good to know, Paul. I haven't opened the machines yet, so I don't know what stepper motors they have and whether I can use their drivers.
But what I found was that the first typewriter indeed had a stepper motor for the cylinder, too. It has a conical clutch thing, engaged by a solenoid. I'll probably glue the clutch and reuse the solenoid for something else. The vertical resolution of the revolving cylinder is about 70 steps per inch. Much smaller steps than I first measured.
But the horizontal steps of the typewheel carriage might be too large. Perhaps micro stepping can compensate.
Both the Canon and the Brother will turn into plotters! The Canon has 6 wire steppers, which work with 4 wire bipolar drivers. The Brother has 5 wire steppers, which I will control using the original electronics. I'll hijack some IC:s which contain darlingtons that steer the stepper motors.
Here's an image from the Canon. This is the wheel holding the (removed) typewheel. It has a stepper motor directly on same axis:
Note the brass plate under the green disk. And a hole in the brass plate. And a photo diode thing recognising the hole in the brass plate. So if you ever need a stepper motor with some kind of position control, you can try to find that in an old typewriter.
If you want to type characters, hack into the keyboard and keep the electronics intact.
They are usually using a 8x8 matrix of keys. Using two 4051 analog multiplexers you can switch all the keys using 8 I/O pins on the Arduino - quite simple. I've done this a number of times.
That crossed my mind. Though I don't know how convenient it would be. I'm planning on plotting beautiful "handwriting" text. They say teens call typewriters real time printers. It would be a fun programming task with a fifo buffer. But I guess I'd rather prepare the text with a text editor on a computer, before I put the plotter to do the writing.
Well, the Canon typewriter has an LCD. Probably for typing and editing one line at a time before printing. But I’ve already done some harm to the original electronics, so I guess I’ve destroyed my chances to actually take over the character handling logics. The typewriter seems to be from 1987 and I don’t think I’m going to hack into the LCD. But I could still use the keyboard for something.
Well, the Canon typewriter has an LCD. Probably for typing and editing one line at a time before printing. But I've already done some harm to the original electronics, so I guess I've destroyed my chances to actually take over the character handling logics. The typewriter seems to be from 1987 and I don't think I'm going to hack into the LCD. But I could still use the keyboard for something.
Oh, that sucks.
All the printer i've seen with LCD can be put into "direct" mode where it's printing right away, so that could have worked.
Anyhow, since you broke the electronics, you will have to sort out your own. I tried doing that but stopped the project since the old steppers found ind typrwriters are high-voltage (30-45V), high-inductance motors, not suited for "modern" hybrid-stepper-drivers unfortunately.
If the darlington-drivers on the PCB are still ok, i would just remove the CPU and drive the darlington-drivers directly from the Arduino.
Well, I've decided that the unipolar 5 wire motors I will drive through the original darlington IC:s (Brother) and the 6 wire motors I will drive as 4 wire bipolars using Sparkfun's EasyDrivers (Canon). The idea of hacking into the Canon LCD-keyboard-character handling is way beyond what I originally intended to do with these typewriters, so I'll probably just leave it.
The Brother seems to run on 12 V. I'll probably just reuse its own power unit. I just have to figure out if 12 V is too much for the Arduino. The Canon uses some 22 V. I have a spare laptop power unit with 18 V 3A, which I intend to use. It will provide voltage and current for the steppers. The stepper drivers in turn will provide the voltage regulating for the Arduino.
I still don't have a clue on whether both typewriters will turn into plotters. If I don't get them to perform half steps or micro steps, I will ditch them.