Thermal Printer Driver Troubleshooting
Hey everyone. I am trying to troubleshoot a thermal printer issue when printing over bluetooth. The printer in question is an Extech 3750T and the software runs on Windows CE. The driver is implemented on top of Winsock and written in C ++. As far as I can tell, the household plugs in by spec.
The problem seems to be that sometimes (about one in ten) when printing an image, the printer just stops. Then, when the next print job is sent, it will output one line (one pixel width) of garbage and print a new page.
The driver is built on top of RTF and converts RTF commands and graphics to printer-specific characters and escape sequences. A developer guide is available here:
http://www.adtech.com.pl/upload/3750T_Developers_Manual.pdf
At this point I'm pretty sure it's not a flow control issue (other than resizing the buffer might help somehow).
One thing that is confirmed is that whenever the printer is screwed down, it sends a paper management character to the device, but by then it is too late to save it.
Also, I think the problem is caused by the image being sent and the text is still printing. A messy hack of just 5 seconds seems to make it go, but this is awkward to implement in a production environment as the text size (font size, weight, etc.) will affect the required latency.
I guess I'm looking for suggestions on how to solve this, not explicit solutions.
Any ideas?
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After about 7 days after that, I got some support from the printer manufacturer and resolved the issue by sending images one line at a time. This particular printer uses an image compression mechanism where a byte represents either 8 bits of a graphic image or can be arbitrarily repeated a maximum of 129 times.
I tried to break the data stream every so many bytes, but it didn't help. I think because the image doesn't like to be split into multiple gears. The problem was transferring one line at a time (roughly 72 bytes).
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