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]

Servo Switch Assemblies


If you are interested in trying out some home automation, but don’t want to get into the potentially dangerous area of hacking your house wiring, consider these servo switches. These allow you to flip a switch, using a servo. They are clean, temporary, and fairly compact. You can purchase them at or download the designs and build your own.

High Frequency Start Box


When welding with an AC arc welder, it is often necessary to “scratch start” them to get the arc going. For those unfamiliar, it is just like it sounds. You drag the head across something just like a giant match. There are some that come with an arc stabilizer or “high frequency starter”. This is preferred, but they can be hard to find. [Bill] shows us how to make one of our own. Though you may have an easy enough time finding a big transformer, you might run into some difficulty finding the capacitors, and tungsten spark gaps. If you manage to get your hands on them, you can follow [Bill]’s schematic and build one of these starters for yourself.

Quick Cheap Remote Outlets


[jwad650] wanted a remote controlled power strip. These are fairly expensive, with a single outlet running roughly $15. He was able to build a 6 outlet version for about $50.  He is using an SIS-7c to decode signals from a universal remote. Each plug is individually controlled by a 3Amp relay. Be careful making this, there’s lots of nasty shock potential in that mess of wires. We recommend that you confine it in an enclosure as well. [jwad650] plans on adding an enclosure, as well as LED indicators and fuses. You can see a video of it in action after the break. If you want more information about working with relays, check out the working with relays writeup.

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