Chariots of Fire

I added my old USB chip (FT 232RL) to the game so that I can both control and get diagnostics from the microcontroller. The MCU runs at 20MHz now and I think it wouldn't keep up with the printer at any slower frequency. Getting diagnostics allowed me to plot the main roller/motor movement sequence:

I had a lot of trouble figuring out when to turn the paper sensor on. To understand what the printer does I had to rebuild the old printer from the pieces I had. And I discovered that there's a lever that is pushed when the printer head moves to the very right. When this lever is pushed - no paper is fetched if the roller turns. And paper fetching is actually done with roller turning backwards. But adding another sensor is a pain so I just deduced from the roller movement when it expects the paper sensor to turn on.

This happens when the roller moves backwards, then sits still for 450-600ms, and then moves again backwards. A few cm after that I will turn the paper sensor on and printing commences. The paper-on period is between the two vertical tics on the image.

Another thing I discovered is that the printer is, well, too fast for my rig. It scrolls paper through at mindnumbing 12cm/second. While my rig can probably do 2-3cm/second. However I can control this by printing my stuff inside a box/frame. That forces the printer to slow down. But even that is not enough, the edges get distorted due to slow movement. I need a stronger stepper motor.

This shows my completed rig, with everything I've built so far attached:

There were a few quirks getting the printing working though. Had to add a few hacks. But after some fiddling it finally started working.

The printed page from this video looks like this:

It is a bit fuzzy but it's mostly down to the printer head being too much distance away from the paper surface, paper being slanted and also the print head itself is slanted. So lots of fiddling to do to get to better quality.

Phase 1 successful. I need to give this project some rest now as I've lagged behind my other responsibilities.