Frequency selection voice control switch circuit

The frequency-selective voice control switch is an audio frequency remote control circuit controlled by a specific whistle tone. It can be used to remotely control the power switches of various household appliances. Compared with radio frequency, infrared and other remote control methods, it has the characteristics of simple circuit, convenient debugging, low power consumption, low cost, small size and passive transmitter. Due to the use of high-Q value inductor coils, the anti-interference ability of the circuit is improved. Working Principle: 　　The complete machine circuit is shown in the figure above. The circuit is composed of amplification, frequency selection, shaping, memory, triggering, execution and power supply. The transmitter is a leather whistle that emits a sound of about 12kHz when it is pinched by hand. The microphone MIC receives the acoustic signal and converts it into an electrical signal, which is amplified by transistors VTl and VT2, and a 12kHz frequency selection loop is formed through the inductor L1 and capacitor c3. When a signal with a frequency of 12kHz appears in the circuit, the circuit resonates and the output is maximum, causing the transistor VT3 that is usually in the cut-off state to quickly saturate, generating a high-level signal close to the power supply voltage at both ends of its collector resistor R8, triggering the IC of the memory unit . Due to the high Q value of the inductor in the resonant tank, its passband is narrow. Because most household environmental noise is below 10kHz, and because the upper limit of the frequency response of ordinary electret microphones is more than ten kHz, the resonant frequency of the frequency selection circuit is determined to be 12kHz. When the IC is triggered by the high level of the previous stage, the circuit flips, and the output level of Q2 terminal also changes, causing the state of transistor VT4 to change, triggering the bidirectional thyristor VS to turn on or off, completing the switch control of the electrical appliance. . The IC in the attached picture uses a CMOS double D flip-flop CD4013. In order to ensure reliable triggering, one of the D flip-flops is connected as a monostable circuit. When pin 11 receives a rising edge high-level signal, because VDl is grounded, Q1 becomes low level and the Q1 output becomes high. level, and charges capacitor C5 through resistor R8. When the voltage on c5 is charged to the transfer voltage of S1 terminal, the Q1 terminal jumps back to high level, and then triggers the bistable circuit composed of the next stage D flip-flop. The time constant of the monostable circuit is T≈0.7R9C5. According to the value in the figure, it only accepts one control signal within 3 seconds, which can effectively overcome the shortcomings of the bistable circuit causing unstable flipping due to triggering reasons. The whole circuit adopts the capacitor step-down method for power supply, so there is no overheating problem and the power consumption is also reduced. Component selection and production. The inductor L1 is wound with the bias coil skeleton used in tape recorders. The inductance is 21mH and is adjustable. The β value of each triode should be greater than 100. After the circuit is welded correctly, first debug it with a low-voltage power supply. Connect the 12V DC voltage to both ends of capacitor C6, and disconnect one pole of DW at the same time. Those who have the conditions can use an audio signal generator to output a 12kHz, 10--20mV signal to both ends of the microphone, and adjust L1 to make the voltage at both ends of R8 the highest. Then remove the signal generator, pinch the pronunciation whistle, and the light-emitting diode LED will respond accordingly. The distance should be 5-7m, and the circuit should also be sensitive. Finally, restore the circuit and connect the 220V AC power supply and load test machine. When the LED lights up, the load should also be powered on. When the LED goes out, the load should also be powered off. Otherwise, check whether the thyristor is connected incorrectly or is damaged. The current capacity of the thyristor should be determined according to the load, but the greater the current capacity of the thyristor, the greater the required trigger current. If it is found that the thyristor is not fully conductive during debugging, the value of resistor R11 can be reduced to Increase the trigger current to completely conduct the triac.