The Commodore SR-1800 calculator, introduced in 1976, is a scientific calculator that has the design principles of Commodore’s earlier models but with a more modern look. Manufactured by Commodore in Japan, this calculator has a distinctive wedge-shaped design with a two-piece matte black plastic case, making it good for both portable and desktop use.
The SR-1800 is powered by 4.5V DC, utilizing three AA batteries housed in a compartment cover/cartridge. It also supports an adapter/charger through a socket on the top side, allowing for flexible power options. The calculator’s dimensions are approximately 76mm in width, 160mm in height, and 38mm in depth, with a weight of 174 grams excluding batteries.
One of the standout features of the SR-1800 is its display: a 12-digit green Vacuum Fluorescent Display (VFD) with the third and twelfth digits reserved for negative signs. The twelfth digit also serves as an error indicator, and the first decimal point indicates radian mode. The display is housed under an oversized, wrap-over green plastic filter, providing a large and bright image.
The SR-1800 offers a good range of mathematical functions, including standard four functions, parentheses, register exchange, reciprocal, squares, square roots, change sign, pi, trigonometric functions, logarithms, powers, nth root, polar/Cartesian coordinates conversion, degree/radian conversion, and statistical calculations. It also features a three-function first memory with a two-function second memory.
The calculator’s design includes small, responsive keys typical of Commodore, with extra raised labels that are painted green. The lower front edge has a metallic sticker with the Commodore branding.
Internally, the SR-1800 is composed of several key components:
- 1 x CPU Commodore GHU-03A 7614 (week 14 of 1976), 40-pin DIL
- 1 x IC Commodore KGHU-01W 7618 (week 18 of 1976), 16-pin DIL
- 1 x 12-digit VFD unit; single tube flat faced
- 2 x transistors
- 8 x diodes
- 5 x capacitors
- 8 x resistors
- 1 x transformer
The main CPU board (PCB No. 200855 TW-17 Rev B) sits above the keyboard assembly (200785 KB-6424-01 SR9120 N) and is connected via a 21-way ribbon cable. The calculator can be disassembled by removing two screws from the rear and gently prying apart the two sections.
Logic:
- The (C) key cancels the last number entered on the first press and clears the entire calculator on the second press.
- There is no constant function available.
- Input overflow is suppressed; entering a ninth digit is ignored.
- Negative numbers are displayed with a “-” in the far left (twelfth) digit.
- Divide by zero and overflow errors display an “E” in the far left digit and are not recoverable.
- The change sign function can be used mid-number entry but not before.
- Negative square roots result in an overflow error.
- Memory functions include (STO1) to store, (RCL1) to recall, and (∑1) to add to memory.
- The (>P) and (>R) keys convert coordinates between polar and rectangular (Cartesian) forms.
- Higher functions are accessed using a two-key sequence with the (F) key.
- The (d-r) key toggles between degrees and radians, with radian mode indicated by a lit decimal point in the far right digit.
- The nth power key (yx) displays the intermediary logarithm on the first press.
- The calculator provides 12 digits of precision.
- The (EEV) and (EE^) keys display the shifted mantissa, useful for converting small numbers to milli- or micro-units.
The SR-1800’s main board is typical of Commodore’s scientific calculators, featuring large connecting ribbon cables and a mini-board for voltage control circuitry. The high component count and use of quality metal brackets show quality construction. Interestingly, the keyboard assembly is labeled SR9120, so it was probably also used for the SR-9120 model.
The Commodore SR-1800 is a nice example of a 1970’s scientific calculator. It offers a range of useful functions and a nice green display. Its construction and component quality reflect Commodore’s commitment to making quality calculators.
