Monday, March 14, 2016

Perhaps a different calculator?

When I started this project I wanted to find a printing calculator with a keyboard that was similar in layout to that of the Busicom 141-PF to serve as an input/output device for my CPU. I vaguely remember looking specifically for calculators with 00 keys, 12-digit capability, and a "number of decimal digits" switch. After looking at a bunch of models in my local Staples office products store I chose the Canon P170-DH Printing Calculator.

This I brought home and immediately disassembled to determine its suitability. It's powered from the A/C mains so I wouldn't have to worry too much about power consumption. I spent quite a while trying to figure out the mechanism for what appeared to be a capacitive- or inductive-sense keyboard before I realized what I'd taken for a meandering sensor trace was actually the gap between two meandering conductors that were bridged by a conductive pad on the bottom of the rubber keypad "spring". Doh! I thought it might be fun to play with the florescent numeric display but really had no need for it in the Busicom replica.  I knew I'd need to figure out how to drive the printer at some point, but I never really looked at it. Having never even turned the thing on I'd assumed it was some sort of dot-matrix or thermal printer.

As the years have gone by I gave thought to buying a second calculator of the same model so I'd have a working copy to compare with the one I planned to hack up, just in case I hadn't really learned enough about it before irreparably disassembling the thing. After all, commodity products don't stay on the market forever.

This evening I decided to see if I could find some sort of documentation on the printer. I opened the shell of the calculator, exposed the printer mechanism and took a real look at it. To my surprise I found it was an impact printer with three print wheels; one prints black numbers, one prints red numbers, and one prints special symbols, and the mechanism that presses the wheel to the paper (or paper to wheel) isn't at all obvious. Wow! Now I really wanted to see what I could dig up on it. I wrote down the numbers printed on the mechanism and exercised my Google-Fu. After finding a couple of Chinese site selling broken mechanisms for spare parts I found another Chinese site selling this calculator wholesale, and that site listed the printer as an Epson M-32TL.

Shifting my search to this string I finally hit paydirt: a memo from a distributor concerning a bunch of Epson printer mechanisms including the M-32TL. Only this was an End-of-Life notice issued a year ago. While I'm not planning on buying the mechanisms myself, this also means that product incorporating this printer mechanism is also likely to be discontinued. I jumped to the Staples website and, sure enough, this model is On Sale due to a "special purchase". Special, in this case, meaning the last of the stock.

Now I'm in a quandary. Do I buy another P170-DH now while I still can, or do I look for a different printing calculator to work from? I still like this one, so I'll get a second.

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