The non-linear nature of the search coils made this challenging however the animated GIF above shows the results are useful enough to show the relative position of the target under the head as well as the strength of the signal.ĭisplay Option 2: Show Signal Trace for Each Search Coil My intention was to use the 4 coils to triangulate the position of the target under the detector head. The net result is that the received pulse width is reduced, this difference in pulse width is measured by the Arduino and displayed on a TFT display in various formats.ĭisplay Option 1: Position of Target under Detector Head
When foreign metal objects come into range of the expanding and collapsing magnetic field this causes some of the energy to be induced into the object in the form of eddy currents. With no objects in range, the baseline pulse width measures approximately 5000 uS. In this design, the received pulse width is determined by the receive coil inductance and a capacitor. The Arduino is programmed to measure the pulse width of the received pulse. This received signal is amplified by the receiving transistor and then turned into a clean digital pulse by a Voltage Comparator and in turn sampled by a Digital Input pin on the Arduino. This current from the pulse causes a sudden magnetic field to form around the coil, the expanding and collapsing field induces a voltage into the Receive Coil. The Arduino produces a pulse which is applied to the Transmit Coil for a very short period of time (4uS) via a transistor. This particular type of metal detector is a Pulse Induction detector which uses separate transmit and receive coils. There are multiple variations of Metal Detector designs. Once you have pinpointed the treasure a single hole centered above each coil enables you to use a wooden skewer to push into the earth so you can start to dig a small plug from the ground reducing damage to the environment.Įach coil can pinpoint detect coins and rings at a depth of 7-10cm so is ideal for looking for lost coins and rings around parks and beaches.Ī Big Thankyou - If you pushed vote button in the top right-hand corner for the "Invention Challenge" and "Explore Science" competitions!!! Incorporating auto calibration, a USB rechargeable power pack, with four different screen modes, frequency, and pulse width adjustment which allows you to customize how you search. This unique metal detector has four search coils, a color touch screen to identify and pinpoint the location of your find. One of the challenges is being able to narrow the exact place to dig to minimize the size of the hole left behind.