I acquired a Trendcom 100 thermal printer some time ago—the Atari 822 is a rebadging of this printer. In a previous post, I mentioned the non-standard 20 pin parallel port connector on the Trendcom, and I was finally able to map it out. I have 8 data pins, the strobe, and the busy pin, but the printer doesn't seem to have a fault pin—there are two pins that appear to be unconnected, but it's nearly impossible to see whether there are any traces going to these pins since they are covered by the connector.
Using an Arduino, I was able to get the printer running. It's a nice little unit, and capable of bidirectional printing. However, I am getting each character (or most of the characters) printed out twice:
I found an article in Analog issue 2 where the author mentions the same issue with the Trendcom 100 when connecting it to an 850 interface—most of the characters are printed out twice. Apparently the solution was to add a .01 (microfarad, I'm assuming) ceramic capacitor to the strobe line to fix the timing.
I had set up the strobe timing in my Arduino sketch based on the values given in the 850 Technical Manual, so I've at least been able to reproduce the faulty behavior:
The original strobe pulse length was 37 microseconds and I was waiting 37 microseconds after putting data on the data pins to initiate the strobe. I've played around with these values a bit and can't seem to get the duplicated characters to go away. The last thing I tried was a strobe pulse length of 70 microseconds and a wait time of 500 microseconds between data stable and start of strobe pulse. Any ideas on what I might be doing wrong?
It would also be great to find some documentation for this printer (or even better documentation for the 822, since I'm assuming it's mostly similar). I haven't been able to find the line feed character code for the Trendcom, so I have to manually advance the paper.