Ultrasonic remote control lighting switch circuit a

This kind of remote control switch has a simple circuit and requires no debugging, making it very suitable for beginners to make.
    working principle. Figure a shows the transmitting circuit. The circuit is composed of discrete components, and can also be composed of NE555. VT1 and VT2 and
R. , E, C1, and C2 form a self-excited multivibrator. The ultrasonic transmitting device B is connected to the collector loop of VT1 and VTZ and works in a push-pull
form loop time constant is determined by R, Ci, and Q. . The resonance frequency of the ultrasonic transmitting device B triggers the multivibrator circuit. Therefore
, this circuit can work at the optimal frequency.
    Figure 18-31b shows the receiving circuit. The junction field effect transistor VT1 forms a high input impedance amplifier, which can match the ultrasonic receiving device B well
and obtain higher receiving sensitivity and frequency generation characteristics. vri adopts self-sufficient bias mode. Changing the wind can change the working
point of VT1. The ultrasonic receiving device B converts the received ultrasonic wave into the corresponding electrical signal. After amplification by the two poles of VT1 and VT2, it is then carried out by VD1 and
VD2 for half-wave Rectified, it becomes a DC signal, which is integrated by G and then acts on VT3 and the base, causing VT3 to change from cut-off to conduction. Its collector
outputs a negative pulse and triggers the JK flip-flop, causing it to flip. The level of the Q terminal of the JK flip-flop directly drives the relay K, causing the auxiliary contact of the relay K
to close or release. The switch of the circuit is controlled by the contacts of relay K. ．