Intelligent lighting following system based on Zigbee wireless sensor network

At present, in China, the problems of high resource consumption and waste are very serious. With the rapid economic growth and the continuous increase in population, the contradiction of insufficient resources has become more prominent, and it is urgent to build a conservation-oriented society. Conservation not only requires reducing consumption, but also improving utilization efficiency. The greatest driving force for building a conservation-oriented society lies in scientific and technological innovation. Energy-saving products have become the goal pursued by society.
ZigBee is a cheap, low-power short-range wireless networking communication technology. Zigbee wireless sensor network has been applied in many places with its advantages of self-organizing network, small size and low power consumption. Based on this, this paper designs an intelligent light following system based on Zigbee wireless sensor network. The system uses Zigbee wireless sensor network and embedded controller to realize that when there are people, the light moves closely with the movement of people, and when there are no people, the light automatically turns off. It avoids the waste of electricity caused by unnecessary lighting for a long time and a large range, and achieves the effect of energy saving.

1 Overall architecture of the system
The topological structure of the deployment of the entire system is shown in Figure 1. The system is based on Zigbee's WSN technology, and uses Zigbee's advantages of low energy consumption, low cost, high scalability, and free frequency band usage fees to build a wireless sensor network. The system can be divided into Zigbee wireless sensor network, embedded control mechanism and actuator. Zigbee wireless sensor network is a star network composed of a coordinator node and several sensor nodes, which is responsible for collecting information on the location of people in the environment; the sensor nodes in the Zigbee network are distributed in every corner of the room and corridor, and monitor the location of people in a specific area in real time. The coordinator node is responsible for establishing and maintaining the network, collecting information collected by the sensor nodes, and transmitting it to the main controller through UART. The main controller analyzes the collected data, determines the location of the person, controls the steering of the servo and the on and off of the light, and realizes the light following function.

2 Hardware Design of the System
The hardware of this system mainly includes three parts: wireless sensor network, embedded device PXA270 and servo, lighting equipment actuator.
2.1 Zigbee wireless sensor network
The core of the wireless sensor network used in this system is a wireless module developed based on CC2430 produced by TI . CC2430 combines a high-performance 2.4 GHz DSSS RF transceiver core and an industrial-grade compact and efficient 8051 controller. It has 8-14 bit ADC, DMA, timing, counter, USABT, AES-128 coprocessor, sleep mode timer, watchdog, power-on reset and power-off detection circuit and 21 programmable pins. It is a true system-on-chip (SoC) CMOS solution. The wireless sensor network in the system consists of a coordinator node and several sensor nodes. The sensor node consists of a data acquisition module, a data processing module, a wireless communication module, and a power module. The circuit diagram is shown in Figure 2.

Connect the human infrared module HC-SR501. HC-SB501 is an automatic control module based on infrared technology. It is designed with the LHI778 probe imported from Germany, with high sensitivity and strong reliability. When a person enters its sensing range, it outputs a high level. When a person leaves the sensing range, it automatically delays the high level and outputs a low level. The OUT output port of the human infrared sensor is connected to the I/O port of CC2430. The I/O port is set to input mode. By detecting the high and low levels of the I/O port, the information of whether a person exists can be obtained. The function of the coordinator node is equivalent to the gateway node. In this system, it acts as hardware to communicate with the main controller. Its composition is shown in Figure 3, including CC2430 RF module, simulation download module, UABT, switch and LED indicator. Zigbee nodes form a star network, and all sensor nodes send the collected information to the coordinator node in real time.
2.2 Embedded control platform and actuators
The main controller used in the system is PXA270 produced by Intel. PXA270 is based on the Xscale core of ARMv5E, with a maximum frequency of 624 MHz. It is an extremely powerful embedded processor. The control mechanism structure of the system is shown in Figure 4. PXA270 is connected to the Zigbee coordinator node through the serial port, and is controlled by the PWM module stacker. The I/O port is connected to the optocoupler chip TPL521-4, and the high and low levels of the I/O port are used to control the conduction and cutoff of the TPL521-4 output. The power line of the lighting device is connected to the output port of TPL521-4 and fixed on the servo, and rotates with the servo.
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3 System software design
3.1 Design of wireless sensor network
The software design of Zigbee node in the system transplants Z-stack protocol stack, which provides complete routing protocol and is completely transparent to the application layer. It only needs to send data to the protocol stack, and the protocol stack will automatically find the path. Therefore, in terms of program development, the program design of coordinator node and sensor node is mainly completed on the basis of Z-stack protocol stack.
1) Software design of coordinator node The
coordinator node is the core of the entire network and is responsible for the establishment and management of the network. The workflow diagram is shown in Figure 5. After the system is powered on, the hardware and protocol stack are initialized first. After the initialization is completed, the protocol stack scans a suitable channel to establish a network. When a device requests to join, the coordinator is responsible for assigning it a 16-bit short address and allowing it to join the network. After the networking is completed, the coordinator node begins to receive data transmitted from the sensor node and transmits it to the embedded controller through the serial port.

2) Design of sensor nodes
The sensor node workflow is shown in Figure 6. It mainly sends the collected personnel information to the coordinator node through wireless transmission. After completing the initialization of CC2430 , it starts scanning the channel, finds a suitable network, sends the network joining information, and after confirmation, it starts to enter the sleep state and waits for the timer to wake up. After receiving the wake-up command, it starts to collect information through the sensor and sends it to its parent node.

3.2 Software Design of Embedded Controller
PXA270 receives the information collected by Zigbee node through serial port, and determines the position of personnel according to Zigbee's 16-bit physical address and the corresponding collected information of whether there is a person. The working process is shown in Figure 7. First, check whether there is a node returning the information of the existence of a person. If there is no one, set the output of I/O port to low level to turn off the light. Otherwise, set I/O to high level and turn on the light. Then, according to the returned Zigbee physical address, judge which node returns the information, so as to determine the approximate position of the person, and then control the steering gear to rotate so that the light shines on this position.

4 System Test
During the experiment, a small model was built in the laboratory. The wireless sensor network included a coordinator node and three sensor nodes (the actual Zigbee node is shown in Figure 8). The sensor nodes were evenly distributed on both sides of the corridor. The PXA270 and lighting device (the actual object is shown in Figure 9) were placed on a higher cabinet.

After the Zigbee node is powered on, about 5 seconds later, the LED display on the development board shows that the network is established. When a person walks by, the light automatically turns on, the servo turns, and shines in the direction where the person is. When the person walks, the servo turns accordingly. When the person leaves the detection area, the lighting device automatically turns off. The experimental results show that the system can work normally.

5 Conclusion
This paper uses wireless sensor technology, Zigbee technology, sensor technology, embedded technology and computer technology to build an intelligent light following system to detect the human body and make the light follow the human body, thereby achieving energy saving and environmental protection. This system has the characteristics of low cost, low power consumption, accurate detection, and strong practicality. It is very suitable for use in corridors, roads and other places, and has good economic benefits and social value. At present, we are still in the experimental stage and are in the process of productization.