The Commodore 385R, released in 1975, represents a notable example of early handheld calculators. Compact and lightweight, the device measures approximately 78.5mm by 104.7mm by 26.9mm and weighs 142 grams with its internal batteries installed, though it weighs only 98 grams without them. Power is supplied through a 6.0V DC internal rechargeable battery that requires 0.2A. It can also operate with an external adapter via a socket on the top. It’s also known as a CBM 385R where CBM stands for Commodore Business Machines.
Encased in a two-piece matt white plastic, the calculator is designed to fit easily in the palm. This case style, typical of early Commodore calculators, is topped by a large plastic plate surrounding a red display filter. The Commodore branding is printed in grey, while the keyboard itself has a matte black surround. The keys, a distinct feature of the Commodore aesthetic, are short-travel and slightly soft but respond reliably to input.
The calculator’s 8-digit red LED display includes an extra position for indicating negative numbers or errors. In terms of functionality, the Commodore 385R offers basic arithmetic operations along with percentage calculations.
Produced in England, the 385R came with a brown, soft plastic carrying case. This case includes a flip-over top and a popper fastener on the front, providing convenience and protection for users on the go.
Under the hood, the Commodore 385R features:
- CPU: GRBP-01-B 7510 (24-pin DIL, date code week 10 of 1975)
- Display Driver: Toshiba T1347 5K (20-pin DIL)
- Display: 9-digit red LED
- Other Components: 1 transistor, 3 diodes, 4 capacitors, 4 resistors, transformer, double cell sealed battery unit
The calculator’s construction is straightforward, allowing the back panel to be removed by unscrewing two long screws. Internally, the keyboard assembly (GICO 50.6.25 L10) is fixed to the front of the unit, located beneath the main CPU board (Part No. 200399, Art No. 200400). The two boards connect via a 13-wire assembly and a small “piggy-back” board containing the DC-DC converter circuit.
Overall, the Commodore 385R is a solid representation of 1970s calculator design, compactly packaged with essential computational capabilities and a straightforward layout. The device reflects Commodore’s approach to user-centered design and durability, common in their early calculators.
