Anton Poluektov Updates the OpenRPNCalc with New PCB Housing, Silkscreened Labels
"Transitional revision" brings with it circuit changes for stability purposes, too — and a V3 is in the works.
Physicist and maker Anton Poluektov has revisited his classic OpenRPNCalc project, sharing lessons learned from four years' use of the original and showing off its second-generation replacement.
"The first version of the calculator is still alive, but predictably the stickers have worn out quite quickly, so for revision two I decided to try a different approach: the front panel and keys both made of PCB material, with labels printed as a silkscreen," Poluektov explains of the new calculator. "This version has improvements in both the firmware and (especially) in hardware and enclosure design."
Poluektov released the original OpenRPNCalc back in 2021, as an STMicroelectronics STM32L476-powered build-it-yourself calculator inspired by the SwissMicros DM42 and tailored towards reverse Polish notation (RPN) operation. A custom circuit board, housing switches for its face buttons and a Sharp Memory LCD, was housed in a 3D-printed case with stickers labeling each button — though, as Poluektov says, these didn't stand the test of time.
The redesigned OpenRPNCalc uses the same STMicro STM32L476 microcontroller and Sharp Memory LCD, but that doesn't mean the underlying circuit is unmodified: Poluektov's changes for the second generation include additional filtering capacitors for the microcontroller and the display, to match the manufacturers' recommendations, the addition of a small tantalum capacitor in parallel with the battery to avoid resets during heavy computation on a low charge, a power connector for powered debugging, a new battery holder to reduce overall thickness, and a more compact PCB overall.
The stickers for labels are gone, too, along with the 3D-printed case: the new revision uses a layered PCB approach instead, with the primary advantage being the ability to use silkscreened labels — something which should withstand a lot more finger-poking than its predecessor.
More information is available on the project's Hackaday.io page, while the latest revision has been published on GitHub under the permissive MIT license. "I consider it a transitional revision," Poluektov warns anyone looking to build their own, "and already see some further improvements to be made for rev. three."