Here is a simple pulse metal detector based on the A1015, JRC4585 and NE555 circuit (impulsnik-dlya-metallopoiska). Instead of the IRF740, after testing, a more powerful IRF530 was used, which works fine without any modifications. The metal detector is currently powered by a 9V battery.

Pulse circuit for metal detection

The handle of an old lawn mower with adjustable length and a piece of PVC pipe were used as a hand. A 37 cm coil (16 turns of 0.4 mm wire) was used. It is possible to expand its capabilities with a second parallel 20 cm coil using an additional switch. Of course, there is no discrimination here. In addition to the elements of the original design, two more diodes were used. One of them serves as a power indicator (green), and the other is connected between the plus and ground of the speaker and serves as an information indicator about the detection of an object – it lights up and blinks when detected.

The range (depth) here depends on the magnetic field strength when the pulse occurs, that is, on the number of turns and current.

 The dynamics of the detector are also important – detecting small changes against the background of high magnetic field strength values. It is good that the MOSFET is controlled by the driver, because the voltage pulse fronts will be steep. And the higher the current, the better. The metal detector can consume several hundred mA from a 9 V battery, so the circuit works better with a powerful power source. The limitation here is the maximum voltage of the 555 chip, which is 16 V. After testing, we can say that the device works quite well: it reliably detects large objects at a distance of up to 70 cm.

Original Post