Simplest detector practice
Emphasis: how the frequency varies depending on the characteristics of the metal and the frequency of work used by the circuit. If the work frequency is very high, then the metal can be regarded as a short loop, it will reduce the inductance detecting inductance, so that the working frequency of the oscillator frequency oscillator rises; if the job is low enough to ignore the eddy current losses, this detector is likely to distinguish black metal or black metal.
Compared with the method of making simple metal detector metal detectors and other types, the working principle of the circuit is this: when the change of inductance inductance coil with detection, L oscillation frequency is changed
1, to produce a frequency oscillation coil is higher than that of 200Hz oscillator is very difficult, so the oscillation circuit oscillation frequency by about 300KHz, so it is easy to make the inductor, only a coaxial cable according to the diagram in size around a turn is made.2 、 the circuit includes oscillator T1, frequency voltage converter, IC1 and MOS dual operational amplifier IC2. The probe coil has a diameter of 440mm, a value of C1 and C2, and the frequency of the oscillator can be guaranteed to be about 300KHz. If the smaller diameter of the probe is used, the coil needs to be surrounded by more turns.3, the oscillator signal level must be at least 500mVpp, so that the 4046 integrated block can be well driven. At this level, the phase comparator can ensure that the PLL in the integrated block is always locked synchronously. The source follower output on the 10 foot is then sent to the IC2 CA3130 for greater amplification.4. The center frequency of the PLL, that is, the zero of the micro meter at the center, is adjusted by the potentiometer P1. If the op amp's sensitivity is extremely high, the P2 must be carefully and repeatedly tuned. The local sensitivity is adjusted by P3, the potentiometer is connected to the negative feedback loop and the inverting input of the IC2, and a positive feedback is added to the non inverting input of the IC2 by the ammeter and the R10. Of course, you can also use different impedance headers, but change the values of R9, R10, and R11. Note: when detecting metal, the size of the probe is related to the detecting coil.
