Brother Model 827R (Version 1)

Brother Industries, Ltd. was founded already in 1908 as Yasui Sewing Machine Co, in Nagoya, Japan and is today mainly known for their printers and sewing machines and vaguely remembered for their typewriters. Nevertheless entered Brother already in October 1966 with the fully-transistorized Calther 130 the business of electronic calculators before switching in October 1969 with the Calther 412 (12 Nixie tubes) and Calther 514 (14 Nixie tubes) to a mix of Integrated Circuits (ICs) and transistors. Shortly after Texas Instruments introduced in October 1971 the TMS1802NC "calculator-on-a-chip", Brother introduced with the PRO-CAL 408 one of the earliest battery powered, portable electronic calculators.

Here at the Datamath Calculator Museum we acquired in 2024 this Brother Model 827R calculator on our quest to complete the Characterization of Single-Chip Calculator Circuits of the TMS0600 Family, anticipating a TMS0603 Chip based on information from various calculator collectors.

Dismantling the featured Model 827R calculator manufactured in June 1976 in Hong Kong reveals a cost effective design using a small printed circuit board (PCB) centered around a General Instruments C-595-1 single-chip calculator circuit connected to a 9-digit LED Display, a keyboard assembly and powered by 4 AA-sized rechargeable NiCd batteries. Learn how to decipher the 49.6.14 Date code printed on the keyboard assembly of the pictured calculator.

Taking a closer look at the LED Display shows a small, discrete LED mounted to the left of the left-most digit and used as a Memory Indicator.

A rather unusual approach and definitely not what we would expect from a TMS0600 single-chip calculator circuit, typically using the left-most digit of the display for the minus sign, overflow condition and - if available - the memory indicator. Studying the data sheet of the General Instruments C-595-1 Chips shows some features not offered with previously known TMS0600 designs:

Additionally we noticed two features of the algorithm used with the General Instruments C-590 series and usually not present with early Texas Instruments' designs:

Texas Instruments TMS0100/TMS0600/TMS0700 designs usually support the Constant feature only for multiplication and division and the Decimal Alignment is either Float or Fix with a dedicated [Decimal Point] selector switch. Comparing the results of some calculations with a TI-2550 based on the TMS0601 Chip and this Brother 827R demonstrates:

But again, we were hoping to locate a Texas Instruments TMS0603 single-chip calculator circuits instead of the General Instruments C-595-1 Chip inside the featured calculator. We consequently  started comparing online pictures of various Brother Model 827R calculators and finally found a small but important difference! Some Model 827R calculators sport an orange [C] key and some have a red key, instead. A visual "trademark" of the PRO-CAL 408 introduced in 1972 were certainly its large, orange [C] and [CI] keys, why suddenly a red [C] key? Enter Model 827R (Version 2).

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

© Joerg Woerner, May 12, 2024. No reprints without written permission.