Using the HP-75D Barcode Reader

[Martin Hepperle]

Those who own a barcode reader for their HP-75D probably never made use of it.

To remedy this situation, I have written a small "C" program which can be used to generate barcodes from ASCII text.
These codes can be printed out and then read into the HP-75 with an small BASIC program.

I also tried to read them directly from a TFT notebook screen, but this did not work.
The wand needs a reflective black/white surface because of its own LED light source.
I guess, that a device with an E-paper display, like an Amazon Kindle, would work too, if the documents were scaled so that one narrow bar matches exactly one column of pixels.

The barcode generating "C" program has been written with Turbo C on MS-DOS in VirtualBox, but it can also be compiled under Windows or any other system with a "C" compiler.
Even if the character range is currently limited to the 7-bit ASCII set, it is possible to read textual data or programs into the HP-75 without the need for a mass storage solution.

If you have a HP-75 pod, the required decoder ROM is built into it, otherwise you need the Barcode ROM module.
[With the sources available, one could even think about extracting the 3 of 9 reader routines into a LEX file for HP-75Ds without pod or Barcode ROM. However, the firmware is relatively complex and large, so I did not do this.]

Note that the conversion requires some memory. The barcode ROM asks for about 1400 bytes of RAM and both, the TEXT as well as the BASIC file will be present in RAM during the conversion.
Also note that my reader program assumes that each line of barcode starts with a line number. Of course, this can be changed easily.

Martin

Edit 1-APR-2022: small correction in 3of9.c program and documentation - ZIP archive updated.

  HP75D-Barcodes.zip (Size: 323.06 KB / Downloads: 15)

[vassilisprevelakis]

Hi Martin,

you wrote:
> The wand needs a reflective black/white surface because of its own LED light source.

I remember back in the 80s when I placed my HP 82153 wand over the caps lock LED of my BBC micro and then wrote a program to blink the LED and this allowed me to send data and programs from my BBC micro to my HP-41.

Lots of free time back then !!!

**vp

http://www.series80.org

[Massimo Gnerucci]

Thank you Martin for the programs and documentation.

Maybe I will find a new interest in my PODded 75Ds ;)

[Martin Hepperle]

(03-31-2022 10:03 AM)vassilisprevelakis Wrote:  Hi Martin,

you wrote:
> The wand needs a reflective black/white surface because of its own LED light source.

I remember back in the 80s when I placed my HP 82153 wand over the caps lock LED of my BBC micro and then wrote a program to blink the LED and this allowed me to send data and programs from my BBC micro to my HP-41.

Lots of free time back then !!!

**vp

http://www.series80.org

Ah, so you are the one who built the foundation of the old optical TAN system still available in some online banking systems. They have only increased the number of blinking bars to 5 ;-)
[attachment=10490]

Also, see this thread for the HP-41C solution "PGB".

PS: I have updated the 3of9.c program in the attachment in post #1 as it was missing a final "showpage" which resulted in a missing final page of a multi-page barcode Postscript document.