Hackers, makers, and engineers have long had a love affair with number crunching. Specifically with the machines that make crunching numbers easier. Today it may be computers, smart watches, and smartphones, but that wasn’t always the case. In the 50’s and 60’s, Slide rules were the rage. Engineers would carry them around in leather belt pouches. By the early 70’s though, the pocket calculator revolution had begun. Calculators have been close at hand for hackers and engineers ever since. This week’s Hacklet celebrates some of the best calculator projects on Hackaday.io!

We start with [Joey Shepard] and RPN Scientific Calculator. No equals sign needed here; [Joey] designed this calculator to work with Reverse Polish notation, just like many of HP’s early machines. Stacks are pretty important for RPN calculators, and this one has plenty of space with dual 200 layer stacks. The two main processors are MSP430s from Texas Instruments. The user interface are a 4 line x 20 character LCD and 42 hand wired buttons. The two processors are pretty ingenious. They communicate over a UART. One processor handles the keyboard and display, while the other concentrates on crunching the numbers and storing data in an SRAM. The case for this calculator is made from soldered up copper clad board. It’s mechanically strong especially since [Joey] added a bead of solder along each joint. If you want to learn more about this technique check out this guide on FR4 enclosures.

[Joey] definitely improved his solder skills with this project. Every wire and connection, including the full SRAM address and data bus were wired by hand on proto boards. We especially like the sweet looking laser cut keyboard on this project!

Next up is [kodera2t], with A tiny scientific calculator. [kodera2t’s] machine definitely has a tiny OLED display! It actually is more than just a calculator. This project runs enhanced basic (EhBasic). The only problem is that EhBasic is written in 6502 assembly. No worries, [kodera2t] simply runs a 6502 emulator on the ATmega1284 he’s using as his main processor. One of the best parts of this project is the keyboard. Rather than wire up tons of buttons, tactile switches, or rubber membranes, [kodera2t] used a touchscreen – but without the screen part. A restive touch panel sans LCD is wired up to the microprocessor. Paper placed under the touch panel. identifies each button’s function.

Speaking of 6502 processors, [Oscarv] created KIM Uno: A simple KIM-1 replica. Kim Uno is a re-creation of the classic KIM-1 single board computer. The 6502 is emulated with an on an Arduino Pro Mini running an ATmega328. The entire system has been shrunken down to pocket calculator size. KIM Uno has something the KIM-1 never had: An enclosure. Well, at least half an enclosure for [Oscarv’s] unit. Some intrepid KIM Uno enthusiasts have already added full cases to this awesome project. To fit the calculator size, [Oscarv] added a programmable calculator mode to his project. Program storage is via the ATmega328’s 1K of EEPROM, which sure beats the cassette tapes of the original KIM-1!

What do you get when you start with a standard Texas Instruments graphing calculator, then add every feature but the kitchen sink on a daughter board? According to [Sean Dylan Goff], you get CalcHack. CalcHack is designed to be used with any of TI’s black and white graphing calculators. It contains quite a bit of hardware, including two CPUs: an ARM Cortex M4 and an M3, a 9 axis IMU, real-time clock, SD card slot, microphone, speaker, 2.4 GHz radio, and a long list of other features. Like any good classroom hacker, [Sean] designed CalcHack to be a clandestine affair. The user has to enter a password to enable the device. Once running, CalcHack takes over through the calculator’s link port. If the teacher (or boss) comes near, a panic button (the DEL key) causes CalcHack to shut down, returning the user to a normal, boring calculator.

If you need to need more precise calculations, check out our brand new calculator project list! If I missed your project, don’t hesitate to drop me a message on Hackaday.io. That’s it for this week’s Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of Hackaday.io!