A Handy Metal Detector Made with Supplies on Hand
While it's not sensitive enough to scour the sand for valuables, it does make a useful device to check for the presence of metals indoors.
According to Instructables user "rgco," an Arduino, 10m of wire, and a 100 Ohm resistor are all you need to assemble a simple metal detector in minutes. Although it’s not sensitive enough for treasure hunting as you take a stroll down the beach, it does work well in the form of a handheld device that can — as shown in the video below — check a pair of pants for the presence of metals. One could also use it to locate nails in a board, heating pipes in the wall, or analyze the composition of tools and furniture.
To construct the unit, the ~20-60 turn coil is connected to an Arduino Uno or Nano’s pin 8 and 10. The Arduino emits a series of pulses on pin 10, then measures the time it takes for these signal to reach pin 8. The delay for each is proportional to the inductance of the coil, which changes as it gets near a conductor per magnetic eddy current effects. A buzzer is added as well to produce a “clicking” noise when the metal is detected.
To create a practical device, the simple Arduino (Nano) circuit is stuffed inside a large Tic Tac container, with the coil held on by a pair of skewer sticks. With this setup, the project works in a similar manner to wands used at the airport and other high-security areas.