Commodore Minuteman 2SR

Date of introduction:  February 1974 Display technology:  LED-stick
New price:  $69.00 Display size:  8
Size:  6.0" x 3.5" x 1.25"
 153 x 90 x 36 mm3
Weight:  7.4 ounces, 210 grams Serial No:  79097
Batteries:  4*N NiCd Date of manufacture:  mth 03 year 1974
AC-Adapter:  Type MM 3
 6.0V 200mA DC
Origin of manufacture:  USA
Precision:  8 Integrated circuits:  MOS MCS2523, SN75491, ITT 492-5
Memories:   Displays:  National Semiconductor NSN 98B
Program steps:   Courtesy of:  Joerg Woerner

Commodore Business Machines (CBM) introduced with the C110 already in September 1971 their first portable electronic calculator, actually a rebranded Bowmar 901B, better known as Bowmar Brain.

While the C110 was a rather short-lived product, did it pave the way to an incredible success story. Its successor Minuteman 1 was introduced within just a few months and started a completely different design language but still using Bowmar electronics. The next evolution - consequently named Minuteman 2 - replaced first the Bowmar electronics and then the Texas Instruments Klixon™ keyboard with Commodore's own designs. It took another iteration with the Minuteman 2SR to drop even the Texas Instruments calculator chips and replace it with a design from MOS Technology, a company Commodore acquired in October 1976 and fueling in October 1977 a revolution with the PET2001 (Personal Electronic Transactor), the best selling "Personal Computer" of its time.

Calculator Introduction Design Electronics Calculator Chip Keyboard Display
C110 September 1971 Bowmar Bowmar TI TMS0103 TI Klixon Monsanto MAN-3A
Minuteman 1 January 1972 Commodore Bowmar TI TMS0103 TI Klixon Monsanto MAN-3A
Minuteman 2
Version 1
June 1972 Commodore Commodore
TI TMS0103 TI Klixon Monsanto MAN-3A
Minuteman 2
Version 2
September 1972 Commodore Commodore
TI TMS0103 Commodore
Wild Rover Corp.
Monsanto MAN-3A
Hewlett Packard
Minuteman 2SR February 1974 Commodore Commodore
National Semiconductor

The next iteration of Commodore's design language was introduced in 1974 with the Minuteman 3 series of calculators.

Dismantling the featured Minuteman 2SR (MM.2SR) manufactured in March 1974 by Commodore reveals some major changes compared to its predecessor MM.2:

• The rather large Wild Rover Corp. keyboard was replaced with a much smaller keyboard coming right out of a Minuteman 3 calculator
• The six AA-sized rechargeable batteries were replaced with four smaller N-sized cells
• The TMS0103 single-chip calculator circuit was replaced with a MOS MCS2523 chip
• The printed circuit board is much smaller than before and sports significantly fewer components
• The Monsanto MAN-3A 7-Segment LED modules or Hewlett Packard 5082-7450 LED display was replaced with a National Semiconductor module

The printed circuit board (PCB) of the Commodore Minuteman 2SR is centered around a MCS2523 single-chip calculator circuit manufactured by MOS Technology and supported by one SN75491 Segment Driver chip and one ITT 492-5 (SN75492) Digit Driver chip. The remaining components on the PCB are mainly used to generate the necessary supply voltage of the MCS2523 and its clock signal for the internal timing.

The display module of the MM.2SR looks was manufactured by National Semiconductor and used 3 small light bars per segment.

The electronics of the MM.2SR is powered by four N-sized rechargeable NiCd batteries and uses an external Type MM3 charger.

Klixon™ is a trademark of Texas Instruments.

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© Joerg Woerner, October 30, 2021. No reprints without written permission.