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Calculators: Handheld: Commodore Minuteman MM3R (code MT) (aka Minuteman)
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Size (approx): | 75mm
(max) x 105mm x 27mm (max) (w,h,d) Weight 100g excluding batteries |
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Power: |
6.0V DC, internal rechargeable battery. 0.2A. Accepts adapter (undefined) through top end socket in the middle. 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. The red plastic display filter is slightly raised and tilted. Squishy but positive keys. Sticking with the red white and blue key colour scheme this compact calculator just oozes quality. | ||
| Display: | 8 digit LED (flat dot type) and ninth digit for minus sign and error flags | ||
| Features: | Four function plus percentages and three function memory. | ||
| Age: | 1973 | ||
| Manufacturer: | Commodore Business Machines, Inc. Made in the Japan. Serial No. 269955. Code stamp "MT" | ||
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Comments:
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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. It sounds like the 3M bit of the model number represents a three function memory. Very similar to the Commodore MM3MT. |
| Components: | 1 x cpu: Texas TMS0132NC 7346
(date code week 46 of 1973), 28 pin DIL, 0.6" width black plastic 1 x IC: National Semiconductor DM75491N 342, 14 pin DIL, 0.3" width black plastic 1 x IC: Texas SN75492 7347, 14 pin DIL, 0.3" width black plastic 1 x nine digit red LED display: National Semiconductor N98B 346 1 x transistor 4 x diodes 5 x resistors 5 x capacitors 1 x transformer 1 x Ni-Cd Battery pack (size of four "N" series cells) |
| 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 |
| Input overflow is suppressed, keying in a ninth digit is ignored | |
| Negative numbers are shown with a minus sign in the far left (ninth) digit thereby allowing full eight digit negative numbers. | |
| It has switched constant on multiply and divide only | |
| It is semi reverse Polish Notation (RPN) logic: to do 3-5 key in (3)(+=)(5)(-=) to give "-1" | |
| Overflow shows the result and "C" (or "E" if negative) in the far left ( ninth) digit and is not recoverable. | |
| Divide by zero shows "C" in the far left ( ninth) digit and is not recoverable. | |
| Memory overflow shows "n" in the far left (ninth) digit and hooks the calculator up until you press (MT) and view the result | |
| There is no indication of memory store - 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. | |
| No major bugs found |
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This shot shows the
calculator with the rear section removed. A capacitor and two resistors
are situated in the rear section, soldered to the power adapter.
This is why there is a piece of foam on the display - to stop electrical
contact.
Notice that the main cpu IC is placed in its own socket for easy repair - this idea was dropped by 1974 to save costs. The rechargeable batteries are situated with guides in the rear section and sit over the ribbon cable to the display. |
