Simon Boak's SB116 Is a Reverse Polish Notation Love Letter to the Classic TI Programmer

Retrocomputing enthusiast Simon Boak responded to the increasing unreliability of his vintage Texas Instruments Programmer calculator in novel fashion, creating a do-it-yourself alternative powered by an Arduino Nano — complete with professional-looking housing and even a "retail" box.

"My Texas Instruments TI Programmer calculator is an excellent tool when working in [MOS] 6502 assembly and other retro experiments," Boak explains. "However going on 45 years old now the buttons are increasingly unreliable and with no good fix for the problem I took this as an opportunity to design the SB116 as a replacement that better fit my own needs."

The SB116 — named for Boak and the 16-bit integer data type employed by its registers — uses an Arduino Nano microcontroller development board as its computational engine, connected to a 40-button keypad designed to mimic the look and feel of the Texas Instruments original it is designed to replace.

"Look and feel," in fact, appears to have been a central concern in the calculator's design: the hardware is housed in an attractive metal chassis, complete with a 128×64 OLED display panel angled for comfortable desk use. The display uses oversized pixels to provide an attractive user interface for Reverse Polish notation (RPN) calculation — complete with the three aforementioned registers, support for binary, octal, decimal, and hexadecimal bases with addition, subtraction, multiplication, division, AND, NOT, OR, XOR, and shift-left and -right operations.

"It can only work with values in the range -32,768 to 32,767 and with no decimal point," Boak admits of the calculator's relatively few restrictions. "I built this for eight-bit programming projects so there is no need for bigger numbers or decimals. Just a single custom PCB was made for the keypad and the Nano is then soldered directly to this. Wires then join this PCB to the display. The switch on the back then sets the power source to either the USB connector on the back or three AAA cells."

Just in case the calculator's impressive aluminum chassis isn't enough of an aesthetic, bringing the calculator in at a hefty 1.1lbs, Boak also designed "retail" packaging for the gadget — a foam-lined box designed to protect the calculator when not in use, "almost," Boak notes, "as if this was a genuine product form the eight-bit era."

More details are available on Boak's website, while the self-described "messy" source code for the project has been published to GitHub under an unspecified open source license.