The first advantage of this metal detector design is its simplicity and the minimum number of elements in the circuit. The second significant advantage is the sensitivity of the device. Well, the third plus is the elementary setup and high repeatability of the circuit. In other words, this metal detector is just a godsend for a novice radio amateur.
Metal detector parts
- Two BC547 transistors - http://alii.pub/5l6vyg
- Active buzzer - http://alii.pub/67haid
- Light-emitting diode - http://alii.pub/5lag4f
- Resistors: 220 Ohm; 2.2 kOhm; 50 kOhm trimmer - http://alii.pub/5h6ouv
- Capacitors: 22 pF; 100 nF; 4.7 nF - http://alii.pub/5n14g8
- Wire 0.2-0.6 mm.
Scheme and principle of operation
The metal detector circuit is simple, as mentioned earlier. Transistor Q2 contains a switch that switches the active buzzer with an internal oscillator. A high-frequency generator is assembled on transistor Q1.
When power is applied to the circuit, the high-frequency generator starts working.During its operation, it consumes a small amount of current, which is not enough to fully open transistor Q2.
Using resistor RV1 we set the threshold at which the generator operates on the edge and is ready to break.
When a metal object appears above the coil, the generator breaks down and stops self-excitation. As a result, both transistors open and a buzzer whistle is heard, indicating the presence of a metal object next to the search coil.
When the object is removed from the coil, generation resumes and the whistle disappears.
- The reel is wound on a frame with a diameter of 9-12 cm. It contains 40 temples with a tap from the middle.
- Supply voltage 4-9 Volts.
The process of making a simple metal detector
The metal detector circuit can be made by surface mounting or on a circuit board.
We install the parts on the board.
We solder the terminals and bite off the excess length.
We wind the spool on a roll of tape.
We clean the ends of the coil, tin it and solder it to the board.
We install batteries in the box, thereby supplying power to the device board.
The metal detector is ready for use.
All that remains is to adjust the trimmer resistor to maximum sensitivity.
The sensitivity of the metal detector is sufficient to detect a massive metal object at a distance of up to 10 cm. To increase the search range, it is necessary to increase the diameter of the search coil.
