Intelligent real-time light tracking, sensor-based LED street light design

　　1. Design principles

　　The solution is inspired by sunflowers, which have the ability to automatically track the direction of the sun. We designed a solar street light solution that can automatically adjust the direction of the solar receiving panel as the sun's position changes. This design uses a solar power generation device to store electricity to power the system and is interconnected with the mains. During the day, the street light is off; at night, the light is dim, and when someone passes by, the light becomes brighter. When the person moves away from the street light, the brightness gradually decreases.

　　The system has added detection functions such as temperature, humidity, smoke, wind direction, wind speed, and rain. It also detects the current battery voltage, current, and temperature values, and shares information through wireless transmission equipment, making it easier for people to understand the external environment and the working status of the system.

　　2. System module design

　　Atmegal6 is used as the control core, which contains multiple AD conversions and has fast computing speed, meeting the design requirements.

　　Solar panel control: After many tests and calculations, the angle of the sun's rotation every half an hour in different seasons was obtained. The microcontroller uses this to control the rotation angle of the stepper motor, so that the solar panel is always facing the sunlight. When night falls, the solar panel automatically resets.

　　Simple weather monitoring function: Use temperature and humidity sensors, wind speed and direction sensors, and rain sensors to detect the surrounding weather in real time, and then the wireless device transmits the information to the information center.

　　Street light protection and detection function: Use AD to collect the voltage and current values ​​of the system. The controller uses these values ​​to monitor the working status of the system in real time. Once there is an overcurrent phenomenon, the power supply is disconnected and an alarm is issued through the wireless device.

　　Power switching function: The system will monitor the total power in real time. If the total power is lower than the set value, the controller will automatically switch the power supply to the AC power to maintain normal operation of the system.

　　3. Theoretical analysis and calculation

　　3.1 Solar panel light tracking and guidance principle

　　The shadow of street lamps (3 meters high) in Hefei area was observed from 6 to 18 o'clock, and the position of the sun was calculated every half hour. When the solar panel is working, it charges four sets of batteries, ensuring that the system can still work normally in the absence of sunlight for a long time. Since the position and intensity of sunlight are different in different seasons, the position of the solar panel should be changed in time in each season, that is, the angle between the solar panel and the ground should be changed to achieve the maximum effect of absorbing light energy.

　　3.2 The configuration principle of batteries and solar panels

　　Assume that the battery capacity is CB, the peak demand of the solar panel is WP, the working voltage of the solar panel is VS, the actual daily discharge time is hd, the number of consecutive rainy days is Dr, the actual street light power is WB, the system voltage is VB, and the local daylight time is hr. Considering the 20% margin and 20% loss, the capacity of the battery is:

　　The power of the solar panel is:

　　Take the configuration of 10W LED lamp as an example, the system voltage is 12V. The local daily effective light is calculated as 3h, and the daily discharge time is 10 hours (take 7pm to 5am as an example). The controller adjusts the power of LED lamp in different time periods at night, and the actual calculation is 6 hours of daily discharge (the brightness is reduced in the early morning). It meets 7 consecutive rainy days (plus the power consumption the night before the rain, which is 8 days). Current I=10W÷12V=0.8333A, battery capacity W=I×6h×8d, that is, W=40AH. Considering that 20% capacity is reserved for battery charging and discharging, the actual current of the street lamp is above 1A (plus 20% loss, including constant current source, line loss, etc.), the actual battery demand is 40AH plus 20% reserved capacity, plus 20% loss, and the actual battery capacity is 57.6AH after calculation. Therefore, the actual battery is 12V/60AH, so four sets of 12V/15AH batteries are needed.

　　Taking the daily discharge time of 10 hours as an example, after power adjustment, it is actually calculated as 6 hours (power adjustment is the same as the above battery). Considering that the solar panel reserves at least 20% of power, the local effective sunlight is calculated based on an average of 3 hours per day: WP÷18V=(I×6h×120%)÷3h, WP=36W (actual peak demand of the solar panel). However, due to the actual constant current source loss, line loss and other comprehensive factors, the loss is about 20%, and the actual peak demand of the solar panel is:

　　WP=36W×120%=43.2W

　　Therefore, the actual battery panel needs 18V/45W, so two 18V battery panels are needed.

　　4. Hardware Design

　　4.1 Solar Panel Buck-Boost Circuit

　　Since the selected battery only needs a 14V voltage when charging, a voltage conversion circuit is needed to make the voltage reach 14V. Therefore, we use the EK8003 chip, which is a synchronous buck-boost chip that can control the output voltage by outputting PWM waves to make it stable.

　　4.2 Solar Charging Design

　　The chip UC3906 is used to control the battery charging. The chip contains an independent current limiting amplifier and voltage control loop, and the driver on the chip is controllable. The driver output current can reach 25mA, which can directly drive the external series adjustment tube to adjust the output current and voltage of the charging circuit.

　　When the battery voltage or temperature is low, the charge enable comparator can control the charger to enter the trickle charge state. When the driver is cut off, the comparator can also output a 25mA trickle charge current. In this way, when the battery is short-circuited or reversed, the charger can only charge with a small current, thus avoiding damage to the battery due to excessive charging current.

　　4.3 Driver Design

　　4.3.1 Lamp driver design

　　When the street light is started, the brightness of the light needs to be controlled, so the system needs an LED lamp driver to control the brightness of the street light. Based on this, the chip PT4115 is used. The chip has the characteristics of up to 5000:1 PWM dimming ratio, and the chip can be dimmed by inputting PWM waves with different duty cycles.

　　4.3.2 Motor drive circuit

　　The rotation of the solar panel is driven by a stepper motor, and the stepper motor drive circuit uses the L298N motor driver chip. A single chip can drive a four-phase stepper motor, and the circuit design is simple.

　　4.4 Data Collection and Processing

　　The temperature and humidity detection circuit uses the SHT10 sensor, which includes a humidity sensing element and a temperature measuring element, and is connected to a 14-bit A/D converter and a serial interface circuit, with strong anti-interference ability. The current detection uses the CSM006NPT Hall current sensor, and the voltage detection uses the AD detection inside the microcontroller.

　　The wireless transceiver circuit uses nRF905 module, which mainly works in the ISM bands of 433MHz, 868MHz and 915MHz. The chip has built-in functional modules such as frequency synthesizer, power amplifier, crystal oscillator and modulator. The output power and communication channel can be configured through the program. It is very suitable for low-power and low-cost system design.

　　5. Software Design

　　At the beginning of the program, it is determined whether it is night. If not, the solar panel is controlled to face the sun, the general position of the solar panel is adjusted according to the time, and then the solar panel is fine-tuned according to the light intensity. After a period of time (preset half an hour), it is recalibrated, and then charging control is performed; otherwise, pedestrian detection is performed. If there are pedestrians, the light is modulated to the maximum brightness, and gradually dims after the person moves away. If there are no pedestrians, the light is kept dimmer. Next is overcurrent protection. If the system is overcurrent, the power supply is cut off, and a notification message is transmitted wirelessly for repair. If there is no overcurrent, the sensor information is collected and it is determined whether the change in information is greater than the preset value. If it is, the information is transmitted wirelessly, otherwise it returns the judgment of whether it is night.

　　6. Conclusion

　　The real-time light-chasing self-sensing street light system is designed to keep the solar panels facing the sun at all times and store more solar energy. The street lights automatically detect pedestrians around them and intelligently adjust the brightness of the lights. The street lights are equipped with a variety of sensors to monitor weather information and share information through wireless transmission, making people's lives more convenient. The entire system is based on the use of new energy and energy conservation. While ensuring necessary lighting, it effectively saves unnecessary energy expenses. Using solar energy and self-sufficient "survival" has good economic benefits and social value.