# Retrotechtacular: The Theremin Terpsitone

Léon Theremin built his eponymous instrument in 1920 under Soviet sponsorship to study proximity sensors. He later applied the idea of generating sounds using the human body’s capacitance to other physical forms like the theremin cello and the theremin keyboard. One of these was the terpsitone, which is kind of like a full-body theremin. It was built about twelve years after the theremin and named after Terpsichore, one of the nine muses of dance and chorus from Greek mythology.

# Measuring Capacitance Against Voltage

Ceramic capacitors are pretty much the pixie dust of the electronics world. If you sprinkle enough of them on a circuit, everything will work. These ceramic capacitors aren’t the newest and latest technology, though: you can find them in radios from the 1930s, and they have one annoying property: their capacitance changes in relation to voltage.

This is a problem if you’re relying on ceramic caps in an RC filter or a power supply. What you need is a device that will graph capacitance against voltage, and [limpkin] is here to show you how to do it.

Of course capacitance is usually measured by timing how long it takes to charge and discharge a cap through an RC oscillator. This requires at least one known value – in this case a 0.1% resistor – by measuring the time it takes for this circuit to oscillate, an unknown capacitance can be calculated.

That’s all well and good, but how do you measure capacitance against a bias voltage? EDN comes to save the day with a simple circuit built around an op-amp. This op-amp is just a comparator, with the rest of the circuit providing a voltage directly proportional to the percentage of charge in the capacitor.

This little project is something [limpkin] has turned into a Kickstarter, and it’s something we’ve seen before. That said, measuring capacitance against a voltage isn’t something any ‘ol meter can do, and we’re glad [limpkin] could put together an easy to use tool that measures this phenomenon.

# The Beginnings Of An LCR Meter

The inductor is an often forgotten passive electrical elements used to design analog circuitry. [Charles’s] latest proof of concept demonstrates how to measure inductance with an oscilloscope, with the hopes of making a PIC based LCR meter.

It is not that often one needs to measure inductance, but inductors are used in switching regulators, motor circuits, wireless designs, analog audio circuitry, and many other types of projects. The principles of measuring inductance can be used to test inductors that you have made yourself, and you can even use this knowledge to measure capacitance.

[Charles] originally saw a great guide on how to measure impedance by [Alan], and decided to run with the idea. Why spend over \$200 on an LCR meter when you can just build one? That’s the spirit! Be sure to watch [Alan’s] and [Charles’s] videos after the break. What kind of test equipment have you built in order to save money?

# Mobile Chicken Coop Includes Wireless Sensors

In and of itself this mobile chicken coop is a pretty nice build. There are some additional features lurking inside which you don’t find on most coops. [Neuromancer2701] built-in a set of sensors which can be accessed wirelessly. It makes it a snap to check up on the comfort of the hens without leaving the couch.

At the heart of the sensor system is an Arduino along with an Xbee module. The build isn’t quite finished yet, but so far three sensors have been implemented. A thermistor is used to read the temperature inside the coop. To make sure there’s enough water, two sheets of foil tape were applied to the water reservoir. The CapSense library measures the capacitance between these plates which correlates to the water lever (we’ve seen this type of water level sensor before). And finally, there’s a sensor that can tell if the door to the coop is open or shut.

He’s having trouble automating the door itself. This can be pretty tricky, especially if you go for a super complicated locking mechanism like this one.

# Measuring SMD Parts With A Home Brew Version Of Smart Tweezers

SMD parts are great; they allow you to pack more parts on a board, do away with drilling dozens of PCBs, and when done correctly can produce a factory-quality board made in a home lab. There’s one problem with SMD parts; troubleshooting and measuring them. The ideal solution would be something akin to the Smart Tweezers we’ve seen before, but this fabulous tool costs three hundred bones. [Kai] came up with a much cheaper solution: home brew smart tweezers that can be built for a tenth of the cost as the professional model.

What [Kai] built is an LCR meter, basically a tool that measures inductance, capacitance, and resistance in a very, very small form factor. The technique of measuring a part’s properties involves feeding a set frequency into the device and measuring the phase, voltage and current coming out. It’s all wonderfully explained by [Dave] over at EEVblog in one of his earlier videos.

The hardware [Kai] is using includes an LCD display from a Nokia phone, an MSP430-based microcontroller, a very tiny opamp near the tip of one of the points of the tweezer, and a programmable gain amplifier used to measure the components. In testing, [Kai] can measure very low-value components with a +/- 2% accuracy, and larger, more realistic components with +/- 0.25% accuracy. An awesome accomplishment, and much better than the common Chinese meters that can’t measure in the nH/pF/mΩ range.

[Kai] hasn’t gotten his pair of smart tweezers working yet – he still needs to get the circuit up and running and write some software. We’ll keep our readers apprised of [Kai]’s progress, though, and gently convince him to work with Seeed Studio or someone similar to get his version of Smart Tweezers onto maker’s workbenches the world over.

Capacitive touch plants

Here’s a proof of concept for using plants as a capacitive touch sensor. The sensor is simply a hunk of double-sided copper clad board attached to a microcontroller. But it seems to be able to sense what part of the plant is being touched. [Thanks Fabien]

Adding wireless charging to a Nokia N900

This hack is quite common, but it’s still fun to see what hardware is being outfitted with an inductive charger. This time it’s a Nokia N900 that’s ditching the charging cables.

Wii carrying suitcase from a plastic tackle box

This Wii carrying case (translated) looks great and cost just a few bucks. It started as a tackle box for carrying around your fishing lures. But a bit of creative cutting and there’s a place for everything.

Browser based schematic and board layout

There’s a new kid on the block when it comes to circuit design. Circuits.io offers in-brower schematic design and board artwork layout. [Thanks ADIDAIllinie (and a few others)]

Bender-o-lantern

Halloween rapidly approaches and we hope that [Tim’s] carving of Bender in a pumpkin will inspire you to send in your own Halloween projects.

# NES Controller Uses Capacitive Touch Instead Of Buttons

Here’s one way to really keep the component count low. [David] developed an NES controller that doesn’t use any buttons. The copper clad has been milled to provide a pad which registers a button push based on capacitance. The board has a SIL header at the top, making it easy to plug into the Arduino board that reads the inputs.

[David] had trouble getting the Arduino pin read functions to respond fast enough for he NES console’s expectations. He ended up using commands to access the ATmega’s peripherals directly in order to achieve the target timing. Speaking of, he did his own sniffing of the communication scheme using a logic analyzer. The results of that work, as well as the board files and code are available at the site linked above. And there’s a demo of the controller used to play Super Mario Bros. in the clip after the break.

This is actually a tangential project using a PCB mill which he’s developing through Kickstarter. This certainly shows that the mills works as designed.  Continue reading “NES Controller Uses Capacitive Touch Instead Of Buttons”