Kit parameters:

Power supply voltage: 3-5VDC, the kit is powered by a 3V 2302 battery;

Uses: game entertainment, security inspection, search of metal products on the body, including mobile phones, controlled knives, etc.

Q1, L1, L2, C2, C3, R1, W form a high-frequency oscillation circuit. Adjusting the potentiometer W can change the gain of the oscillation stage and make the oscillator in a critical oscillation state, that is to say, just start the oscillator. Q2 and Q3 form a detection circuit,

When the circuit oscillates normally, when the oscillating voltage AC voltage exceeds 0.6V, Q2 will be turned on in the negative half cycle to short-circuit C4, resulting in Q3 being turned off; when the detection coil L1 is close to a metal object, an eddy current will be generated in the metal conductor, The energy loss in the oscillation loop is increased, the positive feedback is weakened, the oscillation of the oscillator in a critical state is weakened, and the oscillation cannot even be maintained, so that Q2 is turned off, R2 charges C4, and Q3 is turned on to promote the bee The buzzer sounds. According to the presence or absence of sound, it can be determined whether there is a metal object under the detection coil.

According to this principle, this circuit can be effectively converted into a proximity switch for elevator floor control. (Photoelectric switches are not suitable for many occasions, because the light-emitting device and the light-receiving device will be blocked due to the influence of environmental dust.)

Example 1 of the application of the principle of this metal detector: If you want to detect whether there is a car passing by on a certain road, because the car chassis is 0.5 meters or more from the road, and the cement will be buried at a depth of 5-10CM, so it is buried on the ground. A coil with a diameter of 1 meter can stably, accurately and reliably detect whether there is a car on it, which is of great practical value in highway traffic statistics and parking lot prohibited area statistics.

Example 2 of the application of this metal detector principle: A sensor is required on each floor of the elevator controller to detect whether the elevator has reached the stop position. If a mechanical travel switch is used, there will be life and reliability factors; if a photocoupler is used If so, there will be a long-term dust deposition failure; therefore, the only way is to install a metal detector to determine whether the circuit is on or off based on the presence or absence of metal. This will have high practical value in many equipment and machines.

DIY parts (board + device) Delivery list:

Component name Quantity

1 PCB board

3V buzzer 1

100UF25V electrolytic capacitor 1

104 ceramic capacitors 2

222 polyester capacitor 2

220K resistor 0.25W 1

2.2K resistor 0.25W 1

100 ohm blue and white potentiometer 1

9018 triode 1

9015 triode 1

9012 triode 1

12D07 toggle switch 1

1 CR2032 battery

2032 battery pole piece 1

Debug method:

The L1 and L2 of this machine use copper conductors on the printed board to form inductances. You do not need to make your own inductances. It is simple and has a very high success rate! The circuit has just used more than ten components, as long as the installation is correct, it can generally work normally. After installation, connect the power supply, adjust the potentiometer to just not make sound (if it is not close to the metal), use the printed board antenna to approach the metal, and it should make a sound at this time. Turn the potentiometer counterclockwise and try again until it meets the requirements.

See question:

The long beep after power-on is because the front oscillator stage did not vibrate. It is possible that the resistors, transistors and other components are misplaced, or there is an inter-turn short circuit or open circuit in the circuit board coil. Please check carefully with a magnifying glass. In addition, the amplification factor of Q2 is too low to make Q3 turn off and it will be long.

Effect: This simple detector can easily, stably and reliably control and measure metal coins, steel plates, iron plates, aluminum plates, computer CDs, etc. with a distance of about 2.5CM from the coil plane (circuit board).

Package Contents:

1*Metal detection parts with shell/without shell, optional

Only the above package content, other products are not included.

Note: Light shooting and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.