BUSICOM LE-80A Calculator from the 70's: Texas "Calculator on a Chip" implementation - Printable Version +- HP Forums (https://www.hpmuseum.org/forum) +-- Forum: Not HP Calculators (/forum-7.html) +--- Forum: Not remotely HP Calculators (/forum-9.html) +--- Thread: BUSICOM LE-80A Calculator from the 70's: Texas "Calculator on a Chip" implementation (/thread-5237.html)

BUSICOM LE-80A Calculator from the 70's: Texas "Calculator on a Chip" implementation - jebem - 11-29-2015 08:59 PM I got this tiny little pocket calculator since some time ago. The seller told me it was working but when I collected it in my mailbox it was not. Basically it doesn't power on. Today I took some time to have a look. This is one of many implementations from different vendors that used the Texas Instruments TMS0105 "Calculator on a Chip" in the 70's. My specimen uses a TMS0105BNC variant and has a date code of 7303 (1973, week 03). As usual, someone forgot the LR1 batteries inside and it leaked corroding the copper traces in the battery holder section. So I have just used an 4 x 1.5V AA external battery holder to test it. It worked at first try. It uses a Browmar Optostic 9-digit 7-segment LED display. The display is amazing. Look to those tiny dots (LED's) on each segment! The calculator do not have a dedicated "=" key. Trying: 12345679 x 9 += I get this result with a "u" indicator (overflow positive?): By the way, does anyone have information on the indicators used by these TMS0105 processors? Trying: 12345679 x 9 -= I get now two indicators, "-" and "u" (overflow negative?): Entering all eights and I get this "C" indicator: And entering a negative number: (to be continued) RE: BUSICOM LE-80A Calculator from the 70's: Texas "Calculator on a Chip" im... - jebem - 11-29-2015 09:21 PM Dismantling the machine. Despite being so small, it packs no less than 4 printed circuit assemblies interconnected by the good old wire harness: - Keyboard - Processor - Display - Power Supply and Timing Clock As I was in the mood to look a little deeper in the circuit, I hand designed a partial schematics by direct observation. Despite being a standard design, it doesn't use the conventional driver ICs commonly seen in most implementations with this TMS0105 chip. They drive the LED segments anodes directly and use 9 x discrete 3796-28 Si NPN bipolar darlington transistors to drive the LED cathodes. Current consumption using fresh batteries (4x1.5V) is high for such a tiny machine: - One single digit lit: 140mA - All digits lit: 190mA Battery holder showing the corroded contacts.