Doppler microwave automatic switch circuit diagram

The microwave automatic switch is controlled based on the Doppler effect of microwaves . It can monitor the movement of objects and convert the movement into electrical signals to control the lighting of light bulbs or the opening and closing of electrical appliances.

The working principle is as follows. The antenna, T1, C5, etc. form a microwave oscillation circuit. The antenna radiates into the space and generates a microwave field with a radius of about 10m around it. If a person or object moves in the microwave field, it will cause a frequency shift of the microwave. In the circuit It is reflected in the change of the voltage at the antenna terminal . C4 couples this change to the operational amplifier AD for amplification. The output of the operational amplifier AD forms a voltage on R6 through C2. The level of this voltage is related to the distance of the object and the speed of movement, usually in Between 0-3V; op amp AA is connected as a comparator. The reference voltage is 0.4V at 12V. When the voltage on R6 is higher than 0.4V, the high level output of AA is compared with the low level output by comparator AC . D4 When it is turned on and C3 is instantly charged, the voltage of pin 6 of comparator AB is lower than pin 5, and the comparator outputs a high level. If there is no more object moving in the microwave field, the voltage on C3 will be slowly discharged by R9 to form a delay. When 6 When the pin potential is higher than pin 5, the delay ends, and AB outputs low level waiting for the next trigger. The addition of T2, R15, and C6 can keep AC pin 9 low for a period of time (about 5 seconds) after the circuit delay ends , thereby making the circuit reliably reverse and turn off. If it is used for lighting control, it can be combined with "Circuit A". "Circuit A" converts the mains power into a 6V DC power supply for the probe. The triac is used as a switching element to control the light bulb on and off, so that the light will turn on when people arrive and when people leave. Energy saving effect of turning off the lights. If the microwave probe is combined with "Circuit B", a simple microwave anti-theft alarm is formed. As long as someone moves within the monitoring range, the alarm will be triggered, and the loudspeaker will sound a powerful alarm to scare away the criminals.

Component selection: T1 uses UHF tube 9018, f is greater than 700MHz. The antenna is made of an enameled wire with a diameter of 1.5mm, covered with an insulating sleeve, and bent into a ring with a diameter of 90mm. Just use one LM324 for the four operational amplifiers.