Ultrasonic transmitting circuit composed of discrete componentsb

An ultrasonic transmitting circuit composed of discrete components such as T-40-16 is given. As a feedback element, the T-40-16 sensor and
the transistors VTI and VT2 in the circuit form a strong positive feedback frequency oscillator, which converts the electrical oscillation signal into an ultrasonic signal. Its oscillation frequency is equal to the
center frequency of the ultrasonic transmitter T-40-16 40kHz. When the circuit is working, the oscillation waveform generated at both ends of T-40-16 is similar to a pulse square wave, and the voltage
amplitude is close to the electric voltage. When switch S is pressed, a series of 40kHz ultrasonic signals can be emitted to the receiver.
The working voltage of this circuit is -9V, the working current is 25mA, and the remote control distance can reach about 8m.
    Figure 18-60h shows an ultrasonic transmitting circuit composed of MA4 0EIS/EIR and other discrete components . The working principle is the same as Figure 18-60a, except that the sensor uses MA40EIS. Its structure and performance are similar to T-4 0-16. In addition, the inductor L is used as the load resistor on the VT2 collector to increase the excitation voltage , so that the acoustic wave transmitter can emit greater power, and it also improves its resonance characteristics.