Detailed explanation of the principle of metal detector research and development

　　When we do some intelligent control designs, we need to detect the location of metal objects or to detect the presence of metals, such as smart trolley induction iron blocks, robot detection "mines" and metal proximity switches Buying a metal sensor in your usual production is expensive and may not be satisfied with its effectiveness
First, the principle of the circuit metal detector as shown in Figure 1, the inverter IC1 and the peripheral inductorand and capacitor constitute a capacitive three-point oscillator, oscillating frequency is mainly determined by inductor L, capacitor C2, C3, C4 Adjusting the potopotorator RP allows the circuit to be in a newly vibrated state Tiny oscillation signals are amplified by an amplification circuit consisting of IC2 and R1 Then by diode VD rectification, capacitor C5 filter, zui after the inverter IC3 and IC4 for amplification and shaping Two inverted output signals are obtained at the outputs of IC4 and IC5
In the metal detector equipment probe inductor L is not close to the metal object, the circuit normal vibration, oscillating signal through the inverter IC2 amplification and rectifier filtering, in the inverter IC3 input to form a negative voltage, so that the output of IC3 for high level, inverter IC4 output for low level, IC5 output for high level, the light-emitting, beneficial to the controller to pick up the signal When a metal object approaches, the Q value of inductive L drops, causing the circuit to stop Because the input of the inverter IC3 is pulled up to Vcc through the resistor R2, so the output of IC3 is low, IC4, IC5 output are high two, component selection Figure 1 requires the inverter IC1 to work in a linear state, so the CD4069 six inverter integrated circuit is selected Vcc positive power supply, V-negative power supply, power supply voltage can be 3V to 15V (DC), with the completion of the power supply with 5V to achieve a direct connection with the microcontroller
Level and low, the light emitting diode does not light
Inductive L probe is a very important component, its performance is directly related to the sensor's induction performance In the production can have the following options: (1) can choose from the old radio removed with magnetic rod winding inductor, the requirements can make the oscillator normal vibration, but the induction distance is closer, generally around 2cm (2) The selection is about 6 8mH vertical inductor, inductor resistance value of less than 10 o, the greater the resistance of the inductor, the smaller the detection distance (3) Homemade high Q value inductive probe, can be used with the s0 15mm to 0 2mm of paint pack line on the magnetic rod of 10mm around 300 turns, detection distance can reach more than 20cm
Capacitors are polyester capacitors, this needle detector capacitor is relatively stable, diodes can be used 1N4148, potones with small fine-tuning potometers
Third, commissioning and installation of metal detector manufacturers PCB diagram shows that the board size is 37mm x 29mm (if the design size of the patch element will be smaller), all components can be welded on the board, pay attention to set aside the side board to install the inductor, the entire circuit board is installed in a box, to facilitate the inductor detection metal If the oscilloscope can measure square waves at the output, no additional debugging is required Be careful not to use a metal box as an installation box to avoid affecting normal operation The author uses this metal sensor for the detection of metal blocks and non-contact switches in the smart car to achieve good results.