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Lock down project: DIY RedEye Printer
04-22-2020, 11:51 PM (This post was last modified: 04-23-2020 02:18 AM by BobVA.)
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Lock down project: DIY RedEye Printer
Inspired by Meindert's article on an Arduino RedEye interface (based on Martin Hepperle's excellent code and plans), I dug out the HP IR transceiver I'd bought a couple of years ago.

Much as Meindert described, it all went surprisingly smoothly for my first Arduino project. I had to make a couple of tiny changes to the code to get it to compile on the Linux IDE (capitalization in the INCLUDE file names) and that was that - it was capturing IR printing from my HP-25LP and HP-48.

Back to the junk box and I unearthed a little thermal printer module I'd obtained on eBay. It had a TTL serial interface, so the 5v Arduino had no problem driving it, and the slow RedEye data stream meant I only needed two wires (no handshaking lines needed). Martin's default pin assignment works perfectly for this, with the IR receiver on D3, leaving the TXD line free for the printer.

The only software changes were the baud rate (from 115,200 to 9600 bps) and setting the "translateAltCr" flag to TRUE (which suppresses most ESC sequences and, most importantly, changes the 0x04 line ending that HP uses to a regular LF). Both of these items are defined in the sketch (.ino) file.

I did add a procedure and a little code to the "addToBuffer" procedure to remap some special HP characters to the closest symbol in the printer's character set (e.g. pi, divide, right arrow, etc.).

I put the whole mess (printer, HP IR board and Arduino board) in a plastic storage box for a few days of testing. I need to sort out something nicer once I'm sure it's all working.

The only software addition I'm considering is a timer to send the printer a line feed if it's been idle for a few seconds after having printed. Unlike the the HP thermal printers, you can't see the very last line on the print out without advancing the paper.

It's not as sleek as the 82240B and doesn't print graphics but, being a line printer, it is extremely quite and very fast. I'm pretty sure it will replace the 82240B I kept on my desk for check book balancing and tax time.

Thanks Meindert and Martin!!

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Lock down project: DIY RedEye Printer - BobVA - 04-22-2020 11:51 PM

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