Simple version metal detector

Circuit schematic diagram:

Q1 , L1 , L2 , C2 , C3 , R1 and W form a high-frequency oscillation circuit. Adjusting the potentiometer W can change the oscillation stage gain and put the oscillator in a critical oscillation state, which means that the oscillator can just start to vibrate. Q2 and Q3 form a detection circuit. When the circuit oscillates normally, when the oscillation voltage AC voltage exceeds 0.6V , Q2 will conduct in the negative half cycle to discharge C4 and short-circuit, causing Q3 to cut off; when the detection coil L1 is close to a metal object, it will The eddy current is generated in the metal conductor, which increases the energy loss in the oscillation loop, weakens the positive feedback, and weakens the oscillation of the oscillator in the critical state, and even cannot maintain the minimum energy required for oscillation and stops, causing Q2 to cut off, and R2 to C4 Charging, Q3 is turned on, and the buzzer is driven to sound. Based on the presence or absence of sound, you can determine whether there is a metal object under the detection coil.

Debugging method after welding:

L1 and L2 of this machine use copper wires on the printed board to form inductors. There is no need for you to make your own inductors. It is simple and has a very high success rate! The circuit just uses more than a dozen components, and as long as they are installed correctly, they will generally work normally. After installation, connect the power supply, adjust the potentiometer to just stop making sound (when not close to the metal), use the printed board antenna to get close to the metal, it should make sound at this time, and it should stop making sound when it is far away from the metal. If it cannot stop making sound when you are far away, you should put it Adjust the potentiometer a little counterclockwise and try again until it meets the requirements.

See question:

If there is a long beep after power is turned on, this is because the previous oscillation stage has not started to oscillate. 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, if the amplification factor of Q2 is too low to allow Q3 to turn off, it will also beep for a long time.

Video of source of ideas: click to watch

Refer to the column article of Station B: click to view

If you don’t want to DIY, you can buy the TB link (no interest relationship): click to buy