This range meter uses the ultrasonic of about 40 kHz. All of the controls are done by the software of PIC.
The photograph here is the one to have observed the signal when measuring a 2.36m distance. Observation points are shown below.
(1) is 1st pin of IC1 ( It is a signal after the amplification with the operational amplifier. )
(2) is 8th pin of IC3 ( It is a detection holding circuit gate signal by PIC. )
(3) is 11th pin of IC3 ( It is an output signal of the detection holding circuit. )
When (2) is an L level, the detector stops. You can find that a malfunction by the transmission pulse is prevented. The prevention time of this circuit is about 1.5 milliseconds. There is possibility to malfunction when short any more.
Some feeble reflection signals are received until it detects a reception pulse. Because the threshold voltage of the signal detector of IC2 is working effectively, those feeble signals are not detected.
The signal of (3) changes to H level from L level when detecting a reception pulse. This signal is detected by the capture feature of PIC and the propagation time of the ultrasonic is measured.
http://www.hobby-elec.org/e_psrm.htm
