Hacklet 70 – Calculator Projects

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!

calc1We 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!
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A simple Forth development board


Forth is a very interesting programming language. It’s very flexible and is extremely efficient on low powered hardware, but unfortunately not very popular simply due to the fact that it’s not very popular. There were a few Forth-based microcomputers built in the 1980s, but these were largely unsuccessful.

[Leon] is a Forth aficionado and came up with his own Forth development board in the hopes of Forth making a comeback. It’s a very small and cheap board – only about $12 in parts – but it’s still extremely powerful and a fun platform for investigating Forth.

Compared to other programming languages found in 80s microcomputers, Forth is just weird. It’s a stack-based language, so instead of adding two numbers like 3 + 4, Forth uses postfix notation (or Reverse Polish Notation) so the same statement is expressed as 3 4 +. It’s a much more efficient way for computers to handle data, and some claim it’s more efficient for humans as well.

[Leon] created his own board able to be programmed in Forth, shown above, that uses an ATMega328 microcontroller. He’s using AmForth to put Forth on his system, but also extended the base AmForth install with his own floating point version. making this version of Forth at least as powerful as any 80s microcomputer or ATMega development board is today.

[Leon] put together a great demo of the capabilities of Forth and his dev board. You can check that out below.

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Programmable scientific calculator watch

When the band support on [David]’s Casio CFX-400 Scientific Calculator Watch finally broke after 10 years of use, he found it almost impossible to find another watch with the same functionality. Like any good engineer, [David] decided to design a watch to meet his needs. The result of his endeavors was the µWatch, a programmable watch based on a PIC24 with both RPN and Algebraic calculation modes. The watch runs open source software and is expandable thanks to a serial port, an ICSP programming port, and a spot for an infrared LED on the board. On his site, [David] shows how he made the first µWatch and offers kits for anyone who wants to build their own. We’ve been told that the next batch of kits will be made available in 1-2 weeks and are expected to sell out fast.

[Thanks Tomesz]