“Counting box” also saves calculators from small children

[Nathan]‘s son really loves numbers and counting, and one of his favorite things to do is add 1 to a calculator over and over again. Being the awesome dad that he is, [Nathan] built his son a counting box that has a 10-digit rotary switch and two arcade buttons to add and subtract.

One goal of the project was to have the counting box retain memory of the display while being powered off. The easiest way to do this is to write the display data to the ATmega’s EEPROM. This EEPROM is only rated for 100,000 write cycles (although in practice it’s much higher), so [Nathan] included a 24LC256 in a little spasm of over-engineering. All the electronics are laid out on perf board, and the case is constructed from bamboo that was laser cut by Ponoko. The quality of the case itself is fairly remarkable – we’re really impressed with the finish and the magnetic battery access door.

From experience, we know that playing with an HP-15C eventually leads to a broken calculator and having our Nintendo taken away. We’re really happy for [Nathan]‘s son, and wish we had our own counting box at his age.

Gigantic ball-manipulating binary computer

The folks at Evil Mad Scientist Labs just put up a post on the giant mechanical binary computer they brought to last month’s Maker Faire.

As a faithful reproduction of the Digi-Comp II from the 1960s, every operation is powered by balls falling onto levers. Unlike the original, the larger version is powered by billiard balls instead of half-inch marbles. The Digi-Comp II is able to count, add, subtract, multiply, divide, get the 1s or 2s complement and zero all of it’s bits. With a 7-bit accumulator, the Digi-Comp II is able to calculate anything where the result is less than 127, so we wouldn’t recommend doing your taxes on it. In the demo video, it took the Digi-Comp II about two minutes and twenty seconds to multiply 3 by 13. We’re not going to venture a guess on the equivalent seconds per cycle for an electronic calculator, but it’s an impressive build

The Digi-Comp II is a great way to show the process of binary arithmetic in a computer and we were wondering why there aren’t any educational toys like the Digi-Comp II out today. A site linked from the build page tells us there will be kits available this summer, we’re hoping the kit doesn’t fill the bed of a pickup truck.

Check out the video after the break for the multiplication demo.

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Minimalistic 555 Adding Machine

How many 555 timers does it take to add up two 10 digit numbers? [Alan's] 555 Adding Machine does it with 102 of them, he designed the machine as an extreme entry to the 555 contest and the original plan was to make it even more complicated. This machine uses the 555′s to implement a nine decade accumulator and multiplexer, all inputs are managed by an old school dial from a rotary phone which apparently provide nicely timed outputs. Addition and subtraction are achieved using 9s compliment arithmetic which he discusses in the video after the break, for anyone who wants to brush up on 9s compliment or 555 theory.

Alan’s website has some nice pictures (We’re particularly impressed by all that minimalistic soldering) including schematics, and a very nice 33 minute video in which he discusses in detail how the machine works and even offers some history on the Pascaline, which is mechanical calculator that works on similar principles.

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Relay Calculator

Calculators are a handy tool to have around in just about every application. We often take them for granted today, but even when I was a kid they were still sort of expensive devices that you put thought into buying. Illustrating just how far we have come is this awesome Relay Calculator brought to us by [Team 619].

Featuring an optical slider input system, the user can select any two 4 bit numbers and can add or subtract them. Logic is carried out by a couple handfuls of relays setup to be AND, OR, or XOR gates, which are then linked together to build adders.

Output is in binary as well, in the form of lights, though we cant really tell if those are some form of tubes or if they are just rods lit on end. Either way if you require a lot of nibble math and want a conversation starter this suits the bill quite niceley. Otherwise you can keep hooking up more and more relays and maybe one day make your own relay computer.

Join us after the break for a quick video!

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Analog computer does math

This analog computer can multiply, divide, square numbers, and find square roots. It has a maximum result of ten billion with an average precision of 2-3%. [Miroslav's] build recreates something he saw in a Popular Electronics magazine. It uses a resistor network made up of three potentiometers with a digital multimeter is an integral part of the machine. To multiply a number you set the needles on the first two knobs to the numbers on which you are operating. To find the result turn the third knob until the multimeter has been zeroed out and read the value that knob is pointing to. It seems much more simple than some of the discrete logic computers we’ve seen, yet it’s just as interesting.

Make Your Own Odometer from Scraps

For those out there who would enjoy a quick and interesting weekend project, this odometer made by [PeckLauros] is for you. Featured on Instructables it is made from the simplest of materials including some cardboard, a calculator, wires, glue, hot glue, magnetic drive key, an old CD and a reader, and a rubber band.  The magnets, when attached to the CD work in a calculation to add 0.11m to the calculator when a magnet closes the circuit. [PeckLauros] points out that since it is a homebrewed device, it does have flaws such as adding 0.11m twice when the CD is rotated too slowly.  It is easily fixed by simply running faster.  The video is below the break.

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Calc is high-tech for 1970′s homebrew

Just one look at that banner image and you’ve got to be thinking “that’s old”! This 1970′s era home made calculator used a 4-function calculator IC that was quite advanced for its time. The only problem is that the chip couldn’t do anything other than calcuations, which left it up to the maker of this dinosaur to get the display and keypad working. Circuit boards were made by drawing on copper clad with resist marker. These controlled the VFD digits for the IC’s output and also fed it the user inputs.

[Thanks Brian]