555 inductance meter

[Apexys] is performing some experiments with switched-mode power supplies and needed to compare the inductance of the coils he was using. His multimeter doesn’t have an inductance testing function, but he does have a 555 timer on hand. He put the 555 and some other parts together to create his own L meter. The writeup includes the theory behind this meter, with an incoming AC source converted to a voltage by an RC network.

Once he’d worked out the design it was time to build the circuit. Instead of printing a circuit board he created what he calls a DCB; Drawn Circuit Board. We’ve got to admit that this was way faster than using toner transfer or soldering point-to-point. We also like his use of an Erlenmeyer flask and a torch to heat the etchant. We don’t make PCBs in the winter because our Cupric Chloride is too cold to use outside but that may change now. The final piece in the puzzle is an analog meter which he pulled from an extra microamp meter he had on hand. Check out the demo after the break.

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Theory behind evanescent wave coupling, aka wireless power

[Alan Yates] is building a persistence of vision display and needs a way to transfer power from the stationary base to the spinning circuitry. He’s decided to go with wireless energy transfer and he’s sharing all of his research and experiment data from the development process. It comes in two forms, the written version we just linked to, and a 37 minute video which is embedded after the break. If you liked some of the inductive energy transmission devices we’ve featured in the past, [Alan’s] video will fill you in on the why’s and how’s by using a combination of illustrative schematic examples and measurements on test coils that he built.

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Floating globe, hacked to rotate

they need to hire this guy

[Alexy Sha] has done this fantastic hack, where he modified a magnetic floating globe to be motorized and spin on a tilted axis. The original globe was simply levitating via a magnet mounted inside. Though you could spin it by hand, it wasn’t motorized, and actually floated completely vertically instead of being tilted.

[Alexy] wanted to take this idea further and make it automatically spin on a rotated axes. He built a rotation assembly that was basically a motor, hung off-center, attached at the center of the globe. He had to power it via a coil hidden in the base unit, so that it could remain light enough to float. He did a fantastic job and the final product seems like it is the true way it should have been sold.

Check out a video of it in action after the break. We actually like the spinning ring, when he’s testing it, just as much as the final spinning globe.

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Inductive cellphone charging without voiding warranty

[Derek Hughes] wanted to use inductive charging on his cellphone without voiding the warranty. He picked up a Pixi charging backplate meant for a Palm Pre and scavenged the coil and regulator circuitry from it. To make the electrical connection with his HTC HD2 he removed the mini-USB plug from a charging cable and connected it with 30 gauge wire. The whole package will fit beneath the back plate for use with a Touchstone charger (as we’ve seen with the HTC Evo) but there was one problem. The metal backplate from the HD2 interferes with the inductive charging. For now he’s using tape to hold everything together while searching for a plastic case replacement.

He walks you through the hack in the video after the break. We’re usually not worried about voiding warranties, but a phone like this takes a lot of abuse and having warranty protection or even a service agreement isn’t a bad idea. Continue reading “Inductive cellphone charging without voiding warranty”

Robot waits for no man when recharging

Yikes, that power connector certainly wasn’t designed by Apple. Ugly as it may be, it’s the charging cable for a robot and acts as a sensor that allows the robot to properly align and plug into a power receptacle.

We’re going to go off on a tangent for just a second. We often think of the Rat Things from Snowcrash when considering robot power. They were nuclear powered (or something) and instead of recharging required constant cooling. Those day’s aren’t exactly around the corner but we think they’ve been realized in the lawn mowing robots that have a little nests to recharge in. Base stations work but they require the machine to return to the same place, or to have multiple charging stations.

The point is, this specialized cable makes base stations for robots obsolete. Now a robot can plug into any outlet it can get near, a great thing for robots roving large facilities. After the break you can see a video of this process. The robot arm zeros in by scanning horizontally and vertically and measuring the magnetic field put out by the AC in the wires of the outlet. Take a look, it’s a pretty neat piece of engineering.

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McLVDT: a straw-based sensor

We saw [Kevin’s] home-built Linear Variable Differential Transformer in a YouTube video last week and wanted to know more. We’re in luck, he agreed to share all the details as well as a bunch of information on these sensors. An LVDT is used to measure distance along a straight path. Unlike a linear optical encoder, this method uses measurements of inductance between two electrical coils to judge the distance.

[Kevin] used some magnet wire wrapped around two straws of different diameter to fabricate his sensor. A signal generator is connected to the primary coil and the resulting signal induced in the secondary coil is measured to reveal the change in physical position. Check out the video after the break to see the results.

It’s not hard to get your hands on a McDonald’s straw (hence the name ‘Mc’LVDT), a smaller inner straw, and a few feet of magnet wire. This will be a fun one to try when those dark winter days start to get to you.

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