With this pulse metal detector you will be able to find metal, including non-ferrous metal.This is a pulse metal detector (pulse induction PI), which has a good detection depth.
A rectangular signal generator with a frequency of about 130 Hz is assembled on the 555 chip.This signal is sent to a key made on a high-voltage mosfet IRF740.An amplifier and a pulse duration meter are assembled on the TL072 chip.How does such a metal detector work?
The metal detector coil works as a pulse transmitter and receiver.The coil emits an electromagnetic pulse that reaches the metal.Eddy currents are induced in the metal, the pulse of which is received by the coil of the metal detector.This pulse of eddy currents from the metal changes the pulse attenuation signal on the coil.Now it remains to amplify this signal and assemble a pulse duration meter.
The fact that the coil emits pulses can be found out if a coil with a load in the form of a piezo emitter is brought to it.You will hear a sound with a frequency of about 130 Hz
Let’s look at the pulse signal on the coil.We see the rise of the signal and its smooth decline.This is a high-voltage pulse, its voltage reaches about 150 volts.
If there is no metal near the coil, then the pulse drop remains at the same level
And now we bring the metal to the coil and see that the pulse drop has changed, it has become higher on the oscillogram.The pulsed eddy current from the metal does not allow the pulse in the coil to fade quickly
Now a sensitivity check.The metal detector sees a 2 EURO coin at a distance of about 20 cm.A small shovel at a distance of 55 cm and a small lid 60 cm.
The coil of the metal detector has a diameter of 24 cm and contains 27 turns of wire with a diameter of 0.4 mm.The current consumption is about 30 mA.A variable resistor sets the sensitivity level.FR107 diodes limit the high voltage for safe operation of the amplifier.First assemble the generator with the coil and check its operation, whether the coil emits a signal.If there is no reaction to the metal, pay attention to the resistor R7.Try to change his resistance a little.
