Metal Detection Using An Inductor Instead Of A Clock Crystal.

May 8, 2012 by Mike Szczys 13 Comments

This project from a few years back is an interesting take on a metal detector. Instead of building a detection circuit, [Bruno Gavand] replaced the external clock crystal with an inductor. Here you can see the inductor coil next to the PIC 12F683. You can see two components jumping from one breadboard to the other. These are smoothing capacitors on the inductor lines.

The watchdog timer for the chip is run by the internal RC oscillator. When the external crystal receives a pulse due to metal inducing a current in the coil, the value of the watchdog timer is compared to it. This data is filtered and if the proper parameters are present the green LED blinks. This is bicolor LED. If the inductor circuit is functioning properly it will blink red at power up. [Bruno] says that results will vary based on that inductor so you may need to try a few to get the calibration light to blink.

We’re thinking this would make a simple stud finder (by detecting where the nails/screws are in the wall). Check out the demo after the break, then let us know what you would use this for by leaving a comment.

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Barebones PIC RFID Tag

September 26, 2011 by Mike Szczys 34 Comments

An inductor and 8-pin microcontroller are all that make up this barebones RFID tag. You might have done a double-take when first seeing the image above. After all, there’s nothing hooked up to the power and ground pins on the chip. As [Ramiro Pareja] explains in his post, the power is actually supplied via the I/O pins to which the inductor is soldered. It seems that each I/O pin has a parasite capacitor and a pair of clamping diodes inside the chip. When the AC current that is induced by the magnetic field of the RFID reader hits those pins, the capacitors charge and the clamping diodes form a bridge rectifier. This results in power being injected into the chip, which turns around and sends the RFID code back through the inductor.

This isn’t the first time that we’ve seen this concept. We featured a hack that is exactly the same except it used an AVR chip. This one uses a PIC 12F683 but should work with just about any 12F or 16F model. The code is written in Assembly and shouldn’t need any changes for different hardware. [Ramiro] does talk a bit about adding a decoupling capacitor to Vss and Vdd, as well as a tuning capacitor to the two I/O pins used above to help make the device a little more robust. But, as you can see in the video after the break, it works just fine without them.

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Beginner Concepts: A Quartet Of Videos On Inductors

September 22, 2011 by Mike Szczys 18 Comments

Inductors can be found in many of the devices you use every day, but if you’ve been working only with DC in your projects there’s a good chance you’ve never needed to know anything about them. Now’s your chance to pick up on the basics with this video tutorial series. [Afroman] put together four short videos that we’ve embedded after the break. Set aside fifteen minutes to watch them; you’ll be glad you did.

The first in the series starts out by explaining that an inductor is a coil of wire that serves a similar function as a capacitor with one major difference. A capacitor stores voltage, while an inductor stores current. In the second video, [Afroman] hooks up some inductors to a square-wave generator, then measures the resulting current characteristics using an oscilloscope. He shows the difference between inductor core material (air core versus ferrite core) and illustrates the properties that make inductors so useful as filters. The third video covers filtering circuits, and the fourth is the best explanation of why you need a flyback diode when driving a motor (an inductive load) that we’ve seen yet.

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Making EL Wire

August 15, 2010 by Mike Szczys 43 Comments

[youtube=http://www.youtube.com/watch?v=3RKBGxJJmwg]

[Jeri Ellsworth] adds electroluminescent wire to the list of things she makes. The materials list is incredibly low. The common components are epoxy coated magnet wire for the center conductor and bare wire for the second conductor. The part you don’t have on hand is phosphors, although she does link to a source.

The bad news: she doesn’t show us the build process or share the details about the inductor that fires this thing up. The good news: in-depth videos are on the way. In the mean time you can marvel in her glowing success at the end of the video, or check out some of her other electroluminescent fun.

Building A Glue Stick Flashlight

June 9, 2010 by Mike Szczys 29 Comments

Building an LED flashlight is simple, right? Take a battery, connect it to an LED by way of a resistor. Alright wise guy, now make one that steps up the voltage for multiple LEDs and don’t use a boost-converter IC to do so.

[fede.tft] shares a flashlight built inside of a used glue stick case. It’s the perfect size for one AA battery (we’re always on the lookout for good battery cases), and a shape that we’re familiar with as a flashlight. The problem is that he wants two white LEDs but with just one AA cell he’s never going to have more that 1.5V available. He licked that problem, getting to 7.2V by designing his own step-up converter using one transistor, an inductor, and three passive components. To get the inductor he needs, a stock part is disassembled and rewound to suit. Maybe you just end up with a flashlight when all is said and done, but then again, the Sistine Chapel is just some paintings on a ceiling.