Electra Bearcat 210 (BC-210)

While working with Lex on the technology of the Regency "The Touch" ACT-T16K Computer Radio Scanner, he shared in an email to Sean Riddle and the Datamath Calculator Museum that Electra's Bearcat 210 (BC-210) Radio Scanner was actually preceding the "The Touch" and might use a single-chip calculator circuit manufactured by Texas Instruments as "Computing Brain".

Sean immediately acquired a BC-210, de-capped the NB733-03 ML980 marked chip and shared his findings. The mysterious component is obviously a TMS0970 chip in Revision F and part number TMS0973B. Well that's not possible! The BC-210 is known for its large 10-digit 7-Segment LED Display and the TMS0970 is known from the TI-1200 and Little Professor as a cost-effective member of the TMS1000 Microcomputer with 9 digit and 8 segment outputs.

We studied Sean's amazing photos of the TMS0973 from his Bearcat 210 scanner and earlier photos of a TMS0974 from a TI-1270 calculator to find out that Texas Instruments indeed reduced the number of digit outputs of the original TMS1000 from 11 to 9 to maintain the use of a small 28-pin package when designing the TMS0950 but went for the TMS0970 back to 11 digit outputs. With most TMS0970 applications being either replacements of former TMS0950 designs or like four-banger calculators and educational products using only 9-digit or smaller displays, the TMS0970 was "usually" packaged in TMS0950-compatible packages. And with Texas Instruments squeezing one of the two additional digit outputs between the four keyboard inputs, neither schematics nor layouts would look good with the "11-digit" TMS0970.

Understanding that as of today - almost 50 years after the introduction of the TMS0970 - this Bearcat 210 scanner is the only known application unleashing the full potential of the single-chip calculator circuit, we decided to get our own unit for further research of its internals.

Dismantling a Bearcat 210 Radio Scanner with Date code 7732 and manufactured in August 1977 by Electra Company in Cumberland, Indiana reveals a very compact and efficient design with just three printed circuit boards (PCBs):

Here at the Datamath Calculator Museum we consequently focus on the the B733-2 ML980 marked TMS0973B chip and its interaction with the Keyboard-PCB, Display-PCB and other components on the Main-PCB. Lex provided us with the Service Manual of the Bearcat 210 Radio Scanner and Electra provided us with a TMS0973B mounted in a socket for easy repair. The TMS0973B single-chip calculator is using 10 of its 11 R Outputs with discrete transistors to drive the common cathodes of the 10-digit LED display and the 8 O Outputs with external transistors to drive the 7 A to G segments and decimal point of it. The keyboard is connected in a 8*3 matrix to the scanning segment outputs of the TMS0973B and the 3 K2, K4, and K8 Inputs. The remaining R10 Output and K1 Input are used together with the 8 O Outputs to communicate with the Synthesizer through its shift register. Two RS-Latches are used to control Read/Write operation and Data I/O flow and two signals are used for other control of the Synthesizer chip.

Best prerequisite for using our DCM-50A Platform to allow the Characterization of Single-Chip Calculator Circuits of the TMS0970/TMC0900 Family after already studying a TI-1270 (TMS0974) calculator manufactured in July 1976 and a WIZ-A-TRON (TMC0907) educational toy assembled in June 1978.

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, September 5, 2023. No reprints without written permission.