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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Digital Counter From Stuff You Have In Your Junk Drawer

In vehicle racing, a properly tuned suspension is essential for making good time around the track. Weekend Race Warrior [Julian], thought that his right rear suspension might be bottoming out when making hard left turns. After thinking about it for a while, he came up with a super simple way to measure how many times his suspension bottoms out during a lap: a digital counter made from a calculator.

There are two types of calculators out there, one is good for this project and the other won’t work. To figure out which one you have, type in 1+1=. All calculators should display 2. Then, press the = button again. Some calculators will continue to show 2, but some will change to 3, then 4 and so on as many times as the = button is pressed. This is the type of calculator this project requires.

[Julian] opened up his calculator and soldered a pair of wires across the = button terminals. After a hole was drilled in the case for the wires to exit, the calculator was put back together. To count how often his suspension bottomed out, a normally open limit switch was installed on the car at a point where it would be triggered when the suspension bottomed out. The 2 added wires coming out of the modified calculator connect to that switch. Switch presses now emulate a = button press. Before starting a lap, 1+1= is pressed to display 2. At the end of the lap, if the suspension bottomed out, the switch would be triggered and the displayed value would increase. Remember to subtract 2 from that value to get the total number of events that occurred.

A mechanical switch makes this a great application for counting when things move a certain way but there are some more options. Connecting the switch-side of a relay to the calculator allows [Julian] to count brake presses (via the break light signals) or count how often his boost pressure goes over a certain amount (using a pressure switch).

Android Donut Running On A Graphing Calculator

[Josh] is trying to fight a misconception that Android only runs on fast, powerful smartphones. He’s convinced Android will run on extremely low-end hardware, and after a great deal of searching, hit upon a great combination. He’s running Android Donut on a TI nSpire CX graphing calculator.

Unlike just about every other TI calculator, homebrew developers are locked out of the nSpire CX and CX CAS. Without the ability to run native applications on this calculator, [Josh] would be locked out of his platform of choice without the work of the TI calculator community and Ndless, the SDK for this series of calculators.

With the right development environment, [Josh] managed to get the full Android stack up and running and ironed the bugs out. Everything he’s done is available on the GitHub for this project, and with the instructions on the xda developers post, anyone can get a version of Android running on this TI calculator.

While [Josh] has Android Donut running along with most of the 1.6 apps, a terminal emulator, keyboard, WiFi, USB, and Bluetooth running, this calculator-come-Android isn’t as useful as you think it would be. The vast majority of calculator emulators on the Google Play store require Android version 2.2 and up. Yes, [Josh] can still run a TI-83 emulator on his calculator, but finding an app that’s compatible with his version of Android is a challenge.

Still, even with a 150MHz processor and 64MB of RAM – far less than what was found in phones that shipped with Donut – [Josh] is still getting surprisingly good performance out of his calculator. He can play some 2D games on it, and the ability to browse the web with a calculator is interesting, to say the least. It is, however, the perfect example that you don’t need the latest and greatest phone to run Android. Sometimes you don’t even need a phone.

Animated GIFs On A Graphing Calculator

The TI-84 Plus graphing calculator has a Z80 processor, 128 kilobytes of RAM, and a 96×64 resolution grayscale LCD. You might think a machine so lean would be incapable of playing video. You would be right. Animated GIFs, on the other hand, it can handle and [searx] is here to tell you how.

Before assembling his movie, [searx] first needed to grab some video and convert it to something the TI-84 could display. For this, he shot a video and used Premiere Pro to reduce the resolution to 95 by 63 pixels. These frames were saved as BMPs, converted to monochrome, renamed to pic0 through pic9, and uploaded to the calculator’s RAM.

To display the animated GIF, [searx] wrote a small program to cycle through the images one at a time. This program, like the images themselves, were uploaded to the calculator over the USB connector. Playing these animated GIFs is as simple as calling the program, telling it how fast to display the images, and standing back and watching a short flip-book animation on a calculator.

Hackaday Prize Entry: 3D Printed Parametric Motrs

If you’re building something that moves, chances are you’ll be using an electric motor. There are tens of thousands of different motors out there, each with their own properties, speeds, torque, and sizes. How do you pick the right motor? Most of the time it’s a highly educated guess, but [Solenoid] has a better idea: just 3D print a motor designed by a calculator that will give you the properties you need

This entry for The Hackaday Prize is just a web-based calculator for motor designs that takes torque, speed, size, or form factor as an input and spits out a complete motor design. Sure, you’ll need to wind coils on a 3D printed frame, but this calculator removes the need to calculate inductance, coil capacitance, and all the other bits needed to construct an efficient motor.

While actual products made in the millions will still be using off the shelf motors, this project is perfect for one-offs. If you want to motorize a telescope mount, this project will design a motor given the power and resolution per steps required. If you want to build a wind turbine, this calculator will put blades right on the outrunner of a brushless motor. It’s a great project, and something we can’t wait to see the results of.

The 2015 Hackaday Prize is sponsored by:

Relays Calculate Square Roots

After seeing an exhibit of an old relay-based computer as a kid, [Simon] was inspired to build a simple two-relay latching circuit. Since then, he’s been fascinated by how relays can function to do computation. He’s come quite a long way from that first latching circuit, however, and recently finished a huge five-year project which uses electromechanical relays to calculate square roots.


The frame of the square root calculator can hold up to 30 identical relay modules, each of which hold 16 relays on PCBs, for a total of 480 relays. The module-based setup makes repair and maintenance a breeze. Numbers are entered into the computer by a rotary dial from an old phone and stored in the calculator’s relay memory. A nixie tube display completes the bygone era-theme of the device and shows either the current number that’s being entered, or the square root of that number as it’s being calculated.

The real magic of this project is that each relay has an LED which illuminates whenever the relay is energized, which shows the user exactly where all of the bits of the machine are going. [Simon] worked on this project from 2009 and recently completed it in 2014, and it has been featured at the San Mateo Maker Faire and at Microsoft Research in Redmond, WA. We’ve seen smaller versions of this before, but never on this scale and never for one specific operation like square roots.

Video below. Thanks to [Bonsaichop] for the tip!

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High Cost Arduino Calculator Is Unwieldy, Still Cool Though

One of [Kale_3D]’s teachers had made an Arduino-powered calculator. It wasn’t robust and didn’t last too long in the classroom environment. After the non-functional calculator sat around the class for a while, [Kale_3D] decided he would give a shot at repairing it. Along the way the project didn’t just get repaired, it got a full rebuild.

This calculator uses a full 16 button matrix keypad. The Arduino deciphers button pushes with the help of the Keypad library, at which time the appropriate character is displayed on the 2×8 LCD screen. Selecting the function is a little different from normal since this project is limited to 16 buttons. Two of the buttons allow scrolling through not only standard arithmetic functions but trigonometric functions also. This was one of the features that the previous version was not capable of.

To protect the components, an enclosure was made out of 1/4″ laser cut wood. The pieces have notched edges to permit a nice fit. Even so, corner blocks were added to give the case even more rigidity.

Yes, this calculator is not practical, but that’s not the point. In the end [Kale_3D] felt that the project was definitely worth doing. He had learned a bunch of stuff about Arduino and especially code debugging! Most important of all he had a good time building it. There’s a video after the break showing how it works. The code and wiring diagrams are available for download on the project’s Instructable page.

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