DIY High Sensitive Phase-Locked Loop Metal Detector

IC1, CD4011B and L1 and related components constitute the induction oscillator, and RP1 is the frequency fine-tuning potentiometer. The three NAND gates of IC1 constitute the induction oscillation circuit, and the three NAND gates of IC2 and the crystal constitute the local oscillator. The local oscillation signal and the induction signal are differentially frequencyed in a NAND gate of IC1, and the differential frequency signal is output from the ⑧ pin of IC1. Since the IC3CD4046B phase-locked loop circuit and the IC4CD4017B decimal distribution circuit constitute a multi-level adjustable frequency multiplication circuit, the adjustment range is 1~9 times, a total of 9 gears, which can be selected according to actual conditions. The differential frequency signal is input from the (14) pin of CD4046, and the frequency multiplication signal is output from the ④ pin. After passing through the volume potentiometer RP2, it is sent to IC5 (LM386) for amplification and output to the speaker or headphones to release the sound.