Design of human body sensor based on high reliability microwave induction

The microwave induction controller uses a 9 cm diameter micro-loop antenna for microwave detection. The antenna generates an elliptical space microwave alert zone with a radius of 0 to 5 meters (adjustable) in the axial direction. When the human body moves, the reflected echo interferes with the original microwave field (or frequency) emitted by the microwave induction controller and changes. This change is detected, amplified, shaped, multiple compared and delayed by the HT7610A, and then the white wire outputs a voltage control signal.

The high-reliability microwave induction controller consists of a loop antenna and a microwave triode to form a microwave oscillator with an operating frequency of 2.4GHz. The loop antenna can be used as a transmitting antenna and can also receive echoes reflected by human movement. The semiconductor PN junction of the internal microwave triode detects weak frequency shift signals (i.e., human movement signals) after mixing. The microwave-specific microprocessor HT7610A first removes interference signals with too small amplitudes and only converts the detection frequency shift signals of a certain intensity into equal-amplitude pulses with different widths. The circuit only recognizes single signals with sufficiently wide pulses, such as human bodies and vehicles, and its identification circuit is triggered, or there are 2 to 3 narrow pulses within two seconds, such as preventing people from walking 2 to 3 steps in the edge area, and the width detection circuit is also triggered, starting the delay control circuit to work. If it is a weaker interference signal, such as small animals, long-distance tree shaking, high-frequency communication signals, long-distance lightning, and interference generated when household appliances are switched on and off, it should be eliminated. Finally, when the HT7610A identifies a real large object moving signal, the control circuit is triggered and outputs a high level for about 2 seconds, which is displayed synchronously by LED2. The output mode is voltage mode, with a high level (above 4 volts) when there is output and a low level when there is no output.

The clock frequency of the microwave-specific microprocessor HT7610A is 16KH. When the power is first applied, the system will be locked for 60 seconds, during which the microprocessor is initialized and the electric field is established. At this time, LED1 lights up for 60 seconds and then goes out. The system automatically enters the detection state. When a valid signal is detected, a 5-second signal will be output and displayed synchronously by the indicator LED2.

The appearance of the controller is shown in the figure above. There is a sensitivity adjustment hole on the panel, which can adjust the monitoring distance within the range of 1 to 7 meters. The distance becomes farther when turning clockwise, and closer when turning counterclockwise. LED1 and LED2 are used to indicate the working status of TX982. The 1.2-meter-long two-core shielded cable is used to connect the power supply and the load. The red wire is used to connect the positive power supply, the white wire is connected to the output, and the copper mesh shielding layer is connected to the negative pole of the power supply. If necessary, it can be extended to within 50 meters with a similar cable.

The high-reliability microwave induction controller is powered by a 12-16V rectifier converter, and the static power consumption is about 5MA.

The output form is voltage mode. When there is output, it is high level (above 4V), and when it is static, it is low level. Please refer to the figure below for use.

This is the circuit diagram of the microwave human body sensor driving the relay:

High-reliability microwave induction controller works very reliably, generally without false alarms, which is incomparable to the alarm circuits composed of infrared, ultrasonic, pyroelectric components and conventional microwave circuits. It is currently the best product for security and automatic monitoring. Therefore, it is very suitable for use in warehouses, shopping malls, museums or financial departments, with the advantages of concealed installation, large monitoring range and low system cost.

2 Typical Applications

Note: The early high-reliability microwave induction human body sensor used a triode open-drain pull-down output. For application, please refer to the following drawing. The latest high-reliability microwave induction human body sensor uses a level output, which requires slight changes in usage!

The following introduces two practical electronic devices made using high-reliability microwave induction controllers. Their common characteristics are novel and simple circuits, strong practicality, easy production and high cost performance.

2.1 Automatic sensor light

The automatic lamp can automatically identify the brightness of the surrounding light, turn on the light when people come and turn off the light when people leave, without misoperation, high reliability, and the working state of the circuit will not be affected by its own light. It can be widely used in corridors, toilets, courtyards and other occasions to realize automatic lighting.

The circuit of the automatic induction lamp is shown in Figure 1: C1, C2, R1, DW, and D1 form a typical capacitor step-down circuit, which provides 11V DC working voltage to the high-reliability microwave induction controller and CD4011. CD4011BP is a COMS four-NAND gate integrated circuit. When the high-reliability microwave induction controller detects human activity, the white line outputs a pull-down level for 10 seconds, and point A becomes a low level after being inverted by F1 and becomes a high level. R3 and photoresistor GM form a light control circuit. During the day, GM has a smaller resistance value, and point B is a low level after voltage division and is lower than 1/2 of the power supply voltage. NAND gate F2 blocks the output of a high level and charges the voltage on C3 to the power supply voltage through R4. At night, GM has a larger resistance value and point B is a high level. At this time, if someone is active within the monitoring range, F1 outputs a high level, which together turns F2 on to output a low level, which becomes a high level after being inverted by F3 and F4, and turns the bidirectional thyristor BCR on through R5, and the bulb lights up. If the person leaves the monitoring range, TX982 stops outputting point A and turns to high level again, which turns to low level after being inverted by F1, F2 is blocked, and the high level output slowly charges C3 through R4. After about 30 seconds, the voltage on C3 is greater than 1/2 of the power supply voltage, so F3 and F4 flip, and BCR ends and the bulb goes out. The circuit has high reliability, and the corridor lamp made by the stationmaster with this circuit has been working reliably for nearly a year.

2.2 Remote control intrusion alarm

The remote control intrusion alarm is shown in Figure 2: The power supply part consists of a 12V/1.2Ah lead-acid battery and LM317 to form a constant voltage, current-limited floating charge uninterruptible power supply, which can ensure that the battery is always fully charged and can enable the alarm to work normally in the event of a power outage. The floating charge voltage of the lead-acid battery is 14.2V. The LM317 is connected as a constant voltage source, and by adjusting W, the output terminal A can output a stable 14.9V DC voltage.

Resistor R4 can limit the excessive charging current, and D2 can prevent the battery from discharging in reverse after a power outage. TWH9236/9238 is a remote control transmitter and receiver. When any of the A, B, C, and D keys of the transmitter TWH9236 is pressed, the A, B, C, and D output terminals of the receiver TWH9238 will also output a high level and lock the output state.

Here, the A key is set as the intrusion alarm working button, and the other three keys are set as the intrusion alarm release buttons. Therefore, as long as the transmitter A key is pressed, the A output terminal of the receiver will output a high level of about 4 volts and maintain it. When any of the transmitter B, C, and D keys are pressed, the A output terminal of the receiver will become a low level and maintain it. When the A output terminal outputs a high level, the transistor T1 is turned on through the resistor R1, the relay J is energized, and the 12V positive power supply is added to the power supply terminal of the high-reliability microwave induction controller through the relay contact. At this time, the light-emitting diode LED lights up, indicating that the intrusion alarm has worked. After 60 seconds of high-reliability microwave induction controller initialization, the intrusion alarm officially works. At this time, as long as someone enters the monitoring area, the white line output terminal of the high-reliability microwave induction controller will output a pull-down signal for about 10 seconds, turning on T2, and the high-loudness alarm TWH11C will emit a 120dB harsh public security alarm. When the A output terminal outputs a low level, the relay J is disconnected, and the high-reliability microwave induction controller cannot get the working voltage and therefore does not work.

3 Precautions for use

The microwave signal generated by the high-reliability microwave induction controller may cause trace noise during transmission, reflection reception and amplification processing. Excessively increasing the sensitivity will cause false triggering of noise. The sensitivity of being triggered by a human body moving 3 to 4 steps at 7 meters has reached the limit of use and should be adjusted to be triggered by moving 3 to 4 steps at 5 meters for the best result.

High-reliability microwave induction controllers should be installed indoors near the corners, with the axis aligned with doors and windows. Outdoors, attention should be paid to wind and water resistance and the sensitivity should be reduced.

The high-reliability microwave induction controller should be powered by a 12V 100mA DC power supply, and ensure that the power supply voltage is not less than 10 volts at any time to ensure stable operation of the circuit. If the high-loudness alarm and the high-reliability microwave induction controller share a power supply, the power capacity should not be less than 500mA.

The output end of the high-reliability microwave induction controller uses a "pull-down" control method. The positive power supply enters the microwave induction controller through the white line through the relay, causing the relay to flow current and work. Therefore, the voltage measurement method cannot detect whether there is an output.