The ultrasonic transmitter circuit is shown in Fig. 35.8. The transmitter accepts data from the 32-keypads and coverts it into a 24–bit TRD-encoded word. The encoded data appears as a sequential switching waveform at pin 16 of the IC. It is used to turn ON and OFF the stable multivibrator, formed by the two transistors Q1 and Q2 and the associated components.
When the multivibrator is turned ON, it operates at a frequency of 40 kHz and is used to drive the ultrasonic transducer.
Fig. 35.8 Ultrasonic transmitter circuit
The bit period of the encoded word is determined by an oscillator within ...