Based on 555 constitutes an acoustic ohmmeter circuit

Car Audio Crystal 3.2*2.5mm 3225 24M (24.000MHZ) 20PF 10PPM 20PPM 30PPM

One-piece inductor

As shown in the figure, the acoustic ohmmeter consists of 555. This circuit is actually a multivibrator. Since the test lead receives the resistance Rx and is connected in parallel with R3, the resistance is different, and the oscillation frequency is different, the sound level of the speaker is also different. The oscillation frequency f=1.44/[R1+2R2+2(R3//Rx)]C1, according to the level of the sound, the magnitude of the resistance to be measured can be estimated.