The schematic diagram of the monostable ultrasonic receiver circuit. The resonant frequency of the ultrasonic transducer R40-16 is 40kHZ. After the frequency selection by R40-16, the interference signal outside 40kHZ is attenuated. Only the useful signal (transmitter signal) resonating at 40kHZ is sent to the high-pass amplifier composed of VT1~VT3 for amplification. The DC component is detected by C5 and VD1, and the electronic switch composed of VT4 and VT5 is controlled to drive the relay K to work. Since this circuit is only used for single-channel signal amplification, when the transmitter transmits an ultrasonic signal each time, the receiver's relay is energized once (the energization time is the same as the transmitter's signal transmission time), and there is no memory retention function. It can be used for wireless remote control camera shutter control, children's toy control, curtain control, etc. In the circuit, VT1β≥200, VT2β≥150, and other components are self-determined. The circuit can work without debugging. If the sensitivity and anti-interference are not enough, you can check whether the β value of the transistor and the capacity of the capacitor C4 are too far apart. According to actual measurements, with the corresponding transmitter, the remote control distance can reach more than 8m. Indoors, due to wall reflection, there is no directionality. The circuit operating voltage is 3V and the static current is less than 10mA.
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