Sound speed measurement circuit

The J2217 sound speed measuring instrument is used to measure the propagation speed of sound in different propagation media. It can also measure the frequency of sound. The instrument mainly
consists of two sound sensors, a trigger, a sound source, two brackets and 4 wires, and is used in conjunction with the J020l digital timer.
  Here's how it works.
  The trigger of the J2217 sound velocity measuring instrument consists of an acoustic-to-electrical conversion circuit, a frequency-selective amplifier circuit , a shaping circuit, a trigger output circuit and a latch circuit
. The schematic diagram of the whole machine is shown in the figure. This circuit has two identical channels and works exactly the same. The following
is an introduction based on one of them .
    (1) Acoustic-to-electrical conversion circuit When there is sound, the sound pressure generated by the sound wave causes the piezoelectric ceramic sheet Bl to mechanically deform, and
weak voltage signals are formed on the two surfaces of the ceramic sheet to complete the piezoelectric conversion function.
    (2) Frequency-selective amplification circuit The frequency-selective amplification circuit consists of VT1-VT4 and peripheral components. The weak audio voltage signal generated by Bl is first
frequency-selected and amplified by VT1, then voltage amplified by VT2, VT3, and VT4, and output from the collector of VT4. The C- and Li loops connected to the transistor VT1 collector circuit by the frequency-selective network
select audio signals that are close to the natural frequency of the piezoelectric ceramic chip for amplification to improve
the anti-interference ability of the instrument and prevent other sound sources from affecting the instrument. interference.
    In order to reduce the burden on the frequency-selective amplification circuit and prevent the subsequent pulse circuit from interfering with the frequency-selective amplification circuit , an emitter follower VT5 is set up after VT4
. The amplified audio signal voltage is output through the transmitter of VT5 and enters the Shaping circuit 1C1.