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Finding little bits of metal is a time-honored task, right up there with finding free music to download off the Internet. With a metal detector, you can scout out coins in your couch, nails in your walls, keys in somebody’s pocket — face it, the applications are endless.

In this project, we show you how to build a small, handheld metal detector that can detect certain kinds of metal — especially ferrous (iron-containing) metals — even if that metal is under a half-inch or so of drywall, sand, or soil (but never water!).

The Big Picture: Project Overview

In this project, you use an IC that generates an AC signal that goes through a coil. Because metal objects conduct electricity, you can induce a current in those objects. When the coil in the metal detector comes near a metal object, the electromagnetic field in the coil induces currents in the metal object. The electromagnetic field generated by the metal changes the current in the coil.

When the signal changes, IC turns on an LED, alerting you to the presence of metal.

You can see the finished metal detector in Figure 12-1.

Here are the types of activities you’ll be doing to build the metal detector.

You will

1. Build a pretty simple electronic circuit containing a coil, a proximity detector IC, a transistor, a couple of resistors, and an LED.

2. Install the circuit in a box with batteries and an on/off switch.

3. Mount the box on a handle made from plastic pipe.