Microwave detection delay lighting using TX982

This example introduces a microwave detection delay lighting lamp that uses the microwave radar detection module TX982 as the detection device. Its biggest feature is that the circuit working state is not affected by its own light, so it is relatively easy to install. It is suitable for bathrooms, storage rooms, dressing tables, etc., and can make the light turn on when people come and turn off when people leave.

How it works

The circuit schematic diagram of the time-delay lighting lamp made of TX982 microwave radar module is shown in Figure 7-9. It consists of radar detection module IC1, digital circuit IC2, light control circuit, thyristor switch and power supply and other circuits.

The radar detection module IC1 itself has a micro-ring transmitting and receiving antenna. Its basic working principle is that the microwave signal generated by the module is transmitted into space by its own ring antenna, generating a three-dimensional microwave protection zone. When a person or other object moves in the protection zone, the ring antenna will receive the microwave signal reflected back by the person and the moving object. According to the Doppler effect, there will be a slight frequency shift (or phase shift) between this echo signal and the original microwave signal. This change is detected, amplified, shaped, multiple compared and delayed by the internal circuit of the module, and then the module's white output line outputs a pull-down current control signal to control the operation of the subsequent circuit.

Capacitors C1, C2, resistors R1, R2, and diodes VD1, VS form a simple step-down voltage regulator circuit, providing 12V DC working voltage to module IC1 and integrated circuit IC2. When module IC1 detects human activity, its white line output pulls down the level for 10s, making the input end of IC2's NAND gate D1 a low level, and outputs a high level after inversion. R4 and photoresistor RL form a light control circuit. During the day, RL is exposed to natural light and has a small resistance value, so the input end of IC2's NAND gate D2, i.e., pin 5, is lower than 1/2 of the power supply voltage, which is a low level. NAND gate D2 blocks the output of a high level through R5 and charges capacitor C4, and charges it to the power supply voltage. At night, when RL is not illuminated by light, the resistance value becomes larger, and the input end of NAND gate D2, i.e., pin 5, is at a high level. If someone enters the monitoring range at this time, NAND gate D1 outputs a high level, which together turns on NAND gate D2 and outputs a low level. VD3 is then inverted by the parallel NAND gates D3 and D4 to become a high level, and the bidirectional thyristor VTH is turned on through resistor R6, and the lighting lamp EL lights up.

If a person leaves the bathroom, the IC1 module stops outputting, and the input end of the NAND gate D1 resumes high level due to the pull-up resistor R3, and becomes low level after inversion. The NAND gate D2 is blocked, and the output high level is slowly charged to C4 through R5. After about 30s, the voltage on C4 can be made greater than 1/2 of the power supply voltage, thereby realizing the flipping of the NAND gate D3 and the NAND gate D4, outputting a low level, and VTH loses the trigger current. When the AC power passes through zero, it is turned off, and the lighting lamp EL goes out.

Component Selection

IC1 should use the TX982 microwave radar detection module produced by Tianjin Texin Electronics Factory. The module is plastic packaged and has a circular transmitting and receiving antenna. The module is equipped with two LED indicators and a sensitivity adjustment hole, and is equipped with mounting screw holes, so it is very convenient to install. The module is connected to the outside world only through a 1.2m long cable. The red core wire is the positive end of the power supply (12V); the white core wire is the control signal output end, and the internal circuit is an open collector output, so it is a pull-down current output mode; the shielding layer skin net is the ground end, connected to the negative end of the power supply. There is a delay circuit in the module. When the module is powered on for the first time, the system will lock and preheat for 60s, and at the same time complete the initialization of the microprocessor and establish an electromagnetic field. At this time, the red LED lighting lamp on the module housing lights up, and goes out after a delay of 60s, and the system automatically enters the monitoring state. At this time, if someone is active in the monitoring area, the module will have a 10s signal output, and the green LED indicator on the housing will light up and display synchronously. If the human body continues to move, the output signal will continue.

IC2 uses CD4011, CC4011 or MC14011 4-2 input NAND gate digital integrated circuit.

VD1 uses 1N4004 silicon rectifier diode; VD2 uses 1N4148 silicon switching diode; VS is a 12V, 1W silicon Zener diode, such as 2CW110-12V or 1N4724A.

VTH should use MAC94A4 or MAC97A6 type small bidirectional plastic packaged thyristor with smaller trigger current and maximum on-state current of 1 A; EL should use incandescent lamp, fluorescent energy-saving lamp should not be used, and the power should be controlled below 100W.

C1 is required to use CBB/3-400V polypropylene capacitor; C2 and C4 are required to use CD11-25V electrolytic capacitors. The leakage current of C4 is required to be as small as possible, and it is best to use a capacitor; C3 is a CT4 monolithic capacitor.

RL is a MG45 photoresistor; R1 should use a -1W metal film resistor, and the remaining resistors can use RTX-1/8W carbon film resistors.