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Calculators: Handheld: Commodore Minuteman MM3MT

Size (approx): 75mm (max) x 105mm x 27mm (max)  (w,h,d)
Weight 140g including batteries


6.0V DC, internal rechargeable battery. 0.2A.  Accepts adapter (undefined) through top end socket in the middle. This example still works today!  Adapter should be 6V positive centre.
Case: Lovely palm-sized  white matt plastic calculator.  Keyboard surround panel in black plastic and black painted metal display surround.  The latter has a raised and silver painted logo and silver painted on/off label.  Squish but positive keys. Sticking with the red white and blue key colour scheme this compact calculator just oozes quality.
Display: 8 digit LED with no lens, ninth digit for minus sign and error flags
Features: Four function plus percentages and three function memory.
Age: 1974
Manufacturer: Commodore Business Machines, Inc.  Made in the USA.  Serial No. 006487.


The minuteman series was a great concept for sturdy handheld calculators.  The display was a lovely flat LED; the vertical bars being made up of four dots.  Inconvenient memory transfer function, switched constant and those dreaded "+=" type buttons are a pain, however.  It sounds like the 3M bit of the model number represents a three function memory.

Components: 1 x cpu: Texas TMS0132NC 7409 (date code week 9 of 1974), 28 pin DIL
2 x chips: Nat Semi? DM75491N 415 display drivers
1 x nine digit red LED display
1 x transistor
4 x diodes
3 x resistors
4 x capacitors
1 x transformer
1 x GP Ni-Cd Battery pack P/N GP30AAK4BMU 4.8V 300mAh
Boards: Main CPU board is is soldered to the keyboard board underneath.  It has the reference numbers PCB 300531, ART 300532A, ASSY 300533 (with a box for a further mark).  A 17 way ribbon connector joins to the display.
Construction: Remove the two screws on the back and gently prize the calculator back away from the front.  The battery floats but all the boards are attached to the front.

Logic comments: (CE) cancels an incorrect numerical entry, pressing a second time (C) clears the calculator
An error results in the ninth digit showing "C" for overflow, "E" for negative overflow, "n" for memory overflow.  Error status shows result but is not recoverable.
Memory overflow hooks the calculator up until you press (MT) and view the result
Minus sign is displayed in the ninth (far left) digit allowing full eight digit negative numbers.
Input overflow is suppressed, typing in nine digits ignores the last one
There is no memory flag - you have to remember it
The (MT) memory transfer exchanges the memory contents to the current register and also deletes / replaces the memory amount which is rather annoying.
It has switched constant on multiply and divide