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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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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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.
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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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.
Do people enjoy wasting 300$ on a bulky convoluted system, that only works for special “Teacher Edition” calculators, and is several years out of date; E.G. the TI-Presenter? [Benryves] certainly does not. So instead of purchasing a TI-Presenter, he made his own TV out system for the TI brand of calculators by using an ATmega168, a few passive components, and some clever code. The only draw backs being: you save 280$, it fits in your pocket, and it works for almost any TI calculator. Bias aside, the system does actually have a few caveats compared to the commercial edition, but the pros far outweigh the cons.
Sometimes, expensive calculators hit the floor. It’s happened to almost anyone with a graphing calculator from TI or HP. Sadly, they don’t always bounce. After this happened to [Howard C.], an Industrial Engineering student from U. of Iowa, he decided to spend $50 on milling his own replacement case out of aluminum rather than trashing the device over a broken battery compartment. [Howard] chose to send us the story rather than write his own blog, so we’ve included all the great pictures he sent us after the break.
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