The frequency selective voice control switch is an audio frequency remote control circuit controlled by a specific whistle. It can be used to remotely control the power switch of various household appliances. Compared with remote control methods such as radio frequency and infrared, 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 inductor coils, the anti-interference ability of the circuit is improved.
working principle 
The whole circuit is shown in the figure above. The circuit is composed of amplification, frequency selection, shaping, memory, trigger, execution and power supply. The transmitter is a skin whistle. When you squeeze it with your hand, it will make a call of about 12kHz ... The microphone MIC converts it into an electrical signal after receiving the acoustic signal, which is amplified by the transistors VTl and VT2, and forms a 12kHz frequency selection circuit through the inductor L1 and capacitor c3 to select the frequency. When a signal with a frequency of 12 kHz appears in the circuit, the circuit resonates and the output is maximized, so that the normally-off transistor VT3 is quickly saturated, and a high-level signal close to the power supply voltage is generated across its collector resistor R8, triggering the IC of the memory unit. . Because the Q value of the inductance in the resonant circuit is higher, its passband is narrower. Because the domestic environmental noise is mostly below 10kHz, and because the upper limit of the frequency response of the ordinary electret microphone is more than ten kHz, the resonance 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 reverses, and the output level of the Q2 terminal also changes, causing the state of the transistor VT4 to change to trigger the bidirectional thyristor VS to turn on or off, completing the switch control of the appliance . The IC in the figure uses a CMOS dual D flip-flop CD4013. To ensure reliable triggering, connect one of the D flip-flops to a monostable circuit. When the 11th pin receives a high-level signal at the rising edge, VD1 is grounded, making Q1 low and the output of Q1 high. Level, and charge capacitor C5 through resistor R8. When the voltage on c5 is charged to the transfer voltage at the S1 terminal, the Q1 terminal jumps back to the high level, and then triggers the bistable circuit formed by the next-stage D flip-flop. The time constant of the monostable circuit T≈0.7R9C5. According to the value in the figure, only one control signal is accepted within 3 seconds, which can effectively overcome the shortcomings of the unstable flip caused by the trigger of the bistable circuit.
The circuit of the whole machine is powered by the capacitor voltage reduction method, there is no overheating problem, and the power consumption is also reduced.
Component selection and production Inductance L1 is wound with a magnetic coil skeleton for a recorder, the inductance is 21mH, adjustable. The beta value of each transistor should be greater than 100.
After the circuit is welded correctly, debug with low voltage power supply first. Connect a 12V DC voltage across capacitor C6, and disconnect DW to one pole. Those with conditions can use the audio signal generator to output a 12kHz, 10--20mV signal to both ends of the microphone, adjust L1 to make the voltage across R8 the highest. Then remove the signal generator, pinch the whistle, and the LED will respond accordingly. The distance should be 5--7m, the circuit should also be sensitive. Finally, restore the circuit, connect the 220V AC power supply and the load test machine. When the LED is lit, the load should also be powered up. When the LED is off, the load should also be powered off, otherwise it should be checked whether the SCR is connected wrong or damaged. The thyristor should determine its current capacity according to the load, but the larger the thyristor current capacity, the greater the trigger current required. If the thyristor is not fully turned on during debugging, the value of the resistor R11 can be reduced to Increase the trigger current to make the bidirectional thyristor fully conductive.
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