Practical Ultrasonic Switch: Traditional Chinese Circuit Design Guide

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Ultrasonic switchAt present, there are many types of voice-activated switches. The common disadvantage is that any sound can cause the voice-activated switch to operate without any anti-interference ability, which loses its practical significance. At the same time, if you want to make the voice-activated switch operate, you must make a certain sound (such as clapping, shouting or other sounds), which disturbs the tranquility of the environment, so it is not very popular. The sound frequency of the ultrasonic switch introduced in this article is slightly lower than the ultrasonic wave (≥20kHz) range, but slightly higher than the sound wave frequency, so that the human ear has almost no response to the sound wave of this frequency, that is, it cannot be heard. In this way, it not only avoids all kinds of noise interference, makes its operation reliable, but also ensures the quietness and tranquility of the environment. In addition, ultrasonic switches also have the advantages of reliable performance, high sensitivity, simple production, convenient use, low cost and no interference with other electrical appliances.1. Circuit working principleThe circuit principle of the ultrasonic switch is shown in Figure 21-1. It is composed of an ultrasonic generator, an ultrasonic transducer, a sound-controlled integrated circuit, and a regulated power supply. alt="21-1.jpg (29105 bytes)">In the figure, HT is an ultrasonic transducer. It uses the piezoelectric effect of the transducer to convert the ultrasonic signal emitted by the ultrasonic sounder into an electrical signal. It is added to the base of BG2 in a direct-coupled frequency-selective amplifier composed of transistors BG2 and BG3, so that BG1 and BG2 are turned on. The amplified signal resonates at 18kHz through the BG2 collector through the frequency-selective network composed of L and C4. Signals at other frequencies are filtered out, so it has strong anti-interference ability.The amplified ultrasonic signal voltage is output from the collector of BG3 tube and sent to the control terminal ① pin of the sound control integrated circuit IC through the capacitor C6, so that the potential of the output terminal (12) pin changes once, that is, the initial state of pin (12) is low level. After the ultrasonic signal voltage is added to ① pin, pin 12 immediately changes to high level, causing the BG4 tube to conduct, and the relay J acts. When its upper contact is closed, the power switch of the controlled circuit is turned on.When it is necessary to turn off the power of the controlled circuit, just send the ultrasonic signal again and send it to the ① pin of the IC through BG2 and BG3 amplification and frequency selection. Then the IC pin (12) immediately changes to low level, causing the BG4 tube to cut off, and the relay J is released, cutting off the power supply of the controlled circuit.Capacitor C1, diodes D1~D4, transistor BG1 and Zener diode form a capacitor step-down regulated power supply, which provides stable DC power to the ultrasonic switch circuit to ensure reliable operation of the sound control integrated circuit IC and reduce the installation volume of the ultrasonic switch.2. Component selection and debuggingThe IC is a voice-activated integrated circuit, and the SK-1 type voice-activated integrated circuit produced by Beijing Semiconductor Device Factory No. 3 can be used.Ultrasonic sounders and receiving transducers are available for purchase ready-made. The ultrasonic sounder is a rubber ball pressure-type ultrasonic whistle, and its structure is shown in (a) in Figure 21-2. When the rubber ball is controlled by hand, under the action of ball pressure, the air in the ball cavity enters the flute body through the air port. When the airflow passes through the slit, it is accelerated and rushes out quickly. When it impacts the slit edge, ultrasonic waves are generated, which radiate from the wedge-shaped mouth to the silent space through cavity resonance. The resonant sound wave frequency is around 18kHz. …

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