Papercraft dial is the slide-ruler of current limiting resistors


This paper dial makes selecting current limiting resistors a snap. [Giorgos Lazaridis] came up with the tool, which he describes in detail in the Worklog tab of his writeup. If you want one of your own he also posted a PDF which you can print, cut, and tack together.

At this point we can calculate resistor values for LED circuits without looking at reference material. But it wasn’t always like that. This wheel will be a fantastic tool for those just starting out in hobby electronics who are trying to grasp the theory behind lighting up a simple project. The outer wheel references the source voltage, with the inner being a gauge of forward voltage across the LED(s). Line those two values up and you can read the optimal resistor value in the window seen to the right. But wait, there’s more! As you can see in the video after the break the opposite face of the dial also includes a window which will tell you the power dissipation so that you may choose a properly rated resistor. Slick!

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7400 Logic Competition winners announced

The 7400 Logic Competition has drawn to a close. The winners were announced and there are quite a few of them. There were fifteen first place winners named, nine second place, and nineteen third place projects. The bounty of quality entries is a testament to the popularity of the contest. It helps to have a wide range of prizes and the post linked above lists all of the sponsors who donated goodies as an incentive.

The board seen above was awarded the reader’s choice, to which the grand prize was awarded. It is a 7400 series calculator. [Umair Mukati] and [Naveed Ahmed] — both are students at the Institute of Industrial Electronics Engineering in Karachi, Pakistan — developed the device as part of a class project. It is capable of adding or subtracting two digit numbers. This includes support for negative numbers as results. We’ve embedded a video demo of the calculator in action after the break.

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Giving graphing calculators a new life

[Christopher] at Cemetech, ever frequent HaD feature for his hacked up graphing calculators, made it to the NYC Maker Faire.

He already posted on his blog he was making the trip up to Maker Faire, but we were lucky enough to catch up with him. Two things: the name of his blog isn’t ‘cement tech’, but ‘chem tech.’ Apparently he hates it when it’s mispronounced.

Secondly, he’s been turning in the TI-83s for a Casio Prizm graphing calculator. In the video above he tells us he’s gotten a few homebrew games running on the Prizm, a Lua interpreter, and is currently working on digging around the operating system.

[Todd] literally debugs this printing calculator

This printing calculator is a thrift store find. [Todd Harrison] picked it up for a measly $3, and it still works! But the device is about twenty years old and he thinks it’s time to clean up the aging hardware.

After cracking open the case he digs out some of the stuff that has made its way inside. This includes a few dried up moths (debugging complete). While everything is open he gives a tour of the components. The calculator has a VFD which is definitely worth the price tag of the unit even if you just want to reuse the display in another project. But that’s not all. The printing head would be a fun thing to play with as well. We could see using this in projects similar to some of the thermal printer hacks we’ve seen.

When put back together, and given a new ink ribbon, the unit is ready for another 10-years of holding down one corner of your desk. Don’t miss [Todd’s] tear-down and clean-up video after the break.

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Cemetech’s ultimate calculator V2

[Christopher] piped up in our comments on a recent post about using laptop touch pads in other things, noting that he had done this on his Ultimate Calculator Version 2. What he’s done is upgraded his TI-83+ calculator to house a number of improvements and customizations. It now has a stronger RGB backlight so he can illuminate his screen in whatever color strikes his mood. He also integrated a PS2 port so he could use an external mouse/ keyboard. What brought this to our comments though, was the embedded laptop touchpad on the back that is also fully functional. He topped it all off with a rather pleasing paint job as well.

The funny thing is, we caught a glimpse of this thing in a previous post about networking these calculators.

A papercraft resistor calculator from Adafruit

The Adafruit blog just posted a neat papercraft resistor calculator. If you haven’t yet learned the horribly offensive mnemonic for resistor color codes, now’s your chance to have a cheap and portable resistor value reference.

This papercraft resistor calculator is the latest in the family of Circuit Playground tools that include a fabulous electronic reference app we reviewed some months ago. Instead of an Android or iOS device, the papercraft resistor calculator runs on its own mechanical computer; a series of four printed disks and some paper fasteners.

If you’d like to print out your own resistor calculator, Adafruit put up the PDF on GitHub and posted the Illustrator file on Thingiverse for easy editing. It’s not the old-school cool of a slide rule, but we could easily see this resistor calculator being useful if you’re ever lucky enough to teach electronics to children. At least then you won’t have to share that offensive mnemonic.

Antique Electromechanical Calculating Machines

electromechanical calculator Hamann 505

The decision to use electronics for our calculating machines has long been decided.  However, that doesn’t mean that mechanical engineers didn’t put up a valiant, if ultimately futile, fight. [] has an interesting article comparing the calculating technology of the 1960s, such as the [Haman 505], to today’s iPad.

This comparison and pictures were made possible by [Mark Glusker]’s excellent collection.  These models can be divided into two categories, rotary calculators, and printing calculators. According to [Mark]‘s site, the printing calculators stayed on the market a few years after the rotary calculators, which were off the market by 1970.

Although we may never see machines like these made again, anyone even a little bit mechanically inclined would be hard pressed not to be inspired by this collection. Be sure to check out the video of a [Madas 20BTG] calculator after the break to see what one of the rotary models looks like in action! Continue reading “Antique Electromechanical Calculating Machines”