Pulse Metal Detector
Here is a simple pulse metal detector based on the A1015, JRC4585 and NE555. Instead of the IRF740, after testing, the more powerful IRF530 was used, which works properly without modernization. Currently, the metal detector is powered by a 9V battery.
Diagram of a pulse metal detector
A handle from an old 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 20 cm parallel 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 connects between the speaker's plus and ground and serves as an information indicator about object detection – lights up and flashes when detected.
The range (depth) here depends on the strength of the magnetic field when the pulse occurs, that is, on the number of turns and current.
The dynamics of the detector is also important - the detection of small changes against the background of high values of the magnetic field strength. It's a good thing that the MOSFET is controlled by the driver, because the pulse voltage edges will be steep. And the higher the current, the better. A metal detector can draw several hundred mA from a 9V battery, so the circuit works better with a powerful power supply. The limitation here is the maximum voltage of the chip 555, which is 16 V. After tests, we can say that the device works quite decently: it regularly detects large objects at a distance of up to 70 cm.
