Peter Balch's Solve Is a Smart, Espressif ESP32-Powered Pocket Calculator with a 40-Year History
"I wrote the first version of this software in BASIC on a Sharp Pocket Computer around 40 years ago," Balch says.
Maker Peter Balch has designed a custom pocket calculator, built to deliver a rapid solution to multiple equations at once — complete with loop and graphing support: the Espressif ESP32-powered Solve.
"The Solve pocket calculator solves equations numerically," Balch explains of his creation, which is built around an Espressif ESP32-WROOM-32 microcontroller module. "You can use Solve as an ordinary pocket calculator: type in an expression and it will show you the answer. Or you can type in several equations in any order and it will solve them. The equations can be non-linear and simultaneous If they contain 'For Loops' then they will produce a table of answers or plot a graph."
The heart of the build is Espressif's ESP32-WROOM-32 microcontroller, connected to a 2.4" ILI9341-based SPI display with a 320×240 resolution. The custom keyboard is built up of 28 miniature push-button switches, installed on stripboard, with an off-the-shelf battery charging module and compatible lithium-ion battery keeping everything running on-the-move — "or," Balch says, "you could use three AA or AAA cells [and] a battery holder."
The hardware is housed in a custom-designed 3D-printed case, which angles the keyboard and display for more comfortable desk-based operation. For software, Balch created an Arduino version of a project he's been porting for a fistful of decades: "I wrote the first version of this software in BASIC on a Sharp Pocket Computer around 40 years ago," he explains. "Then I rewrote it in Turbo Pascal, then in Delphi-1, then in Delphi-4 and then in C for this project. So the code isn't as pretty as I'd like but it seems to be reliable."
Balch has uploaded instructions for building your own Solve calculator, including 3D print files and source code, to Instructables; "You can build the calculator," he says, "or you can use this Instructable as the basis of your own project that requires ESP32-WROOM-32 microprocessor, a screen and a home-made keyboard."