Metal detectors work well enough if you’re trying to scan the ground for quarters and lost jewelry, but what if you need to, for example, find nails in a tight space? For that job, this “Pocket Metal Locator” works quite nicely, with visual, audio, and haptic metal indication.
The Pocket Metal Locator is shaped sort of like a trowel, but where the digging implement would be, there are instead four programmable LEDs that light up when metal is nearby. When the detecting surface senses a piece of metal, it change from blue-green, to red, to purple. When directly on top of a piece of metal, a buzzer sounds, and a vibration motor shakes.
An Arduino Pro Mini runs the gadget, and senses metal in four sections. It first transmits a signal to each of the four transmitter coils, then measures the inducted power readings on the corresponding receiver coils. If there is metal nearby, this will absorb some of the power that would otherwise go to a receiver, allowing the Arduino to measure this response. A smoothing algorithm in the Arduino code, which along with ongoing changes in the wiring has resulted in a reliable detection device.
Build instructions are available via the link above and print files for the Pocket Metal Locator are available here. Be sure to check it out in action in the video below!