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Devices Electrotechnica Elektrokit
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Metal Detector

Price : INR 380.00

Metal Detector

Metal Detector detects the presence of metal by giving audible warning. This project indicates the presence of ferrous as well as non-ferrous materials depends on the absorption of magnetic energy. An inductor, which forms part of a tuned oscillator circuit, radiates a magnetic field. When a metal object is introduced into this field, enough magnetic energy is absorbed to cause the oscillator to stop working, which causes the output of IC1 high. Transistor T2 turns on and buzzer raises the alarm. IC1 is a Schmitt Trigger IC, which gives output according to the upper and lower threshold voltages set at input pin2 and pin3 respectively.

About the Circuit :
In the circuit diagram, L1 and C1 form an oscillator circuit operates at a frequency of about 70KHz. L1 also serves as a sensor. Because of the high value of resistor R1, the oscillator only just operates. This is desirable; otherwise any losses in the tuned circuit would easily be replenished by the transistor T1.

When the metal object enters in the field induced by L1, the oscillator output is detuned. This output is rectified by diodes D1 and D2 and given to pin2 which is the upper threshold voltage of IC1.This voltage is below the lower threshold voltage at pin3, which is set by R7, R6 and P1. Hence the output at pin6 goes high and T2 turns on. Piezobuzzer connected at the collector of T2 sounds an alarm.

Note : Inductor L1 is not intended to be fitted on the circuit board.

Calibration :

  • If the oscillator does not readily start at any setting of P1, the value of R1 must be reduced. If on the other hand, the oscillator does not stop working when a metal object is held near L1, the value of R1 must be increased. Starting with the wiper of P1 to earth, adjust the preset so that the buzzer just does not operate. If a lower sensitivity is required advance the wiper slightly further.
  • Current consumption is determined primarily by whether the buzzer is energized or not, in any case it is not greater than 50mA.

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