With the wide application of solar LED street lamps in urban lighting systems, how to save energy and improve the utilization of street lamp energy has become an urgent problem to be solved. Solar LED street lamps involve photovoltaic cells, LED lamp heads, batteries and street lamp control systems. Whether solar energy can be used to maximize efficiency and extend the service life of LED lamp heads is an urgent problem to be solved. ZigBee technology provides a suitable solution for the field of street lamp automatic control with its low power consumption, reliable communication and large network capacity [1-3].
This paper studies ZigBee technology and JN5139 mixed-signal microcontroller. Starting from the basic unit of wireless sensor network, illuminance sensor, temperature sensor, DC voltage sensor and current sensor are used to collect photovoltaic cell current voltage, battery current voltage, LED lamp head temperature and Based on the illuminance and other data, a flexible and versatile solar LED street light state sensor node with full-function device (FFD) based on JN5139 module was designed, which made basic work for building high-performance wireless sensor network. The ZigBee technology is combined with the sensor technology to form a network to solve the problems in other control methods: selecting the brightness sensor to collect the illumination of the LED lamp head in real time, reducing the probability of accidentally opening and closing the special environment and special time, and getting rid of the manual intervention.
1 Solar LED street light state sensor node structure
The basic structure of the sensor node is shown in Figure 1. It mainly includes sensors, signal conditioning circuits, A/D converters, microprocessors, RF communication modules, positioning modules, and power modules. The sensor module is responsible for monitoring the collection and data conversion of information in the area; the processor module is responsible for controlling the operation of the entire sensor node, storing and processing the data collected by itself and the data sent by other nodes; the wireless communication module is responsible for wireless communication with other sensor nodes. , exchange control information and send and receive data; the energy supply module provides the required energy for the sensor nodes.
2 sensor node function
A typical ZigBee network consists of three types of nodes: a coordinator, a router, and a terminal device. The coordinator is the central node of the network, responsible for the organization and maintenance of the network; the router is responsible for routing data frames within the network; and the terminal device is the unit that implements specific functions. The node is designed as a full-featured node (FFD) device, which functions as a route, and is responsible for data collection of parameters such as local solar LED street light status, and can realize the following functions:
(1) The sensor node can periodically send the solar LED street lamp state measurement data to the monitoring sub-center;
(2) The sensor node can collect the status data of the solar LED street lamp in real time in response to the requirements of the monitoring sub-center;
(3) sending an alarm message when the sensor node detects that the data exceeds the threshold or its own energy is low;
(4) The solar LED street lamp state data can be automatically stored according to time, and the solar LED street lamp state data at a certain moment can be queried;
(5) Miniaturization, low power consumption, low cost, high reliability, stability and safety.
3 sensor node hardware design
The sensor node is composed of a full-featured device (FFD), and its structural block diagram is shown in Figure 1.
3.1 microprocessor module
As a node in the ZigBee network, low-power design is especially important. After detailed device power comparison, the JN5139 mixed-signal microcontroller is selected as the core of the processor module. The JN5139 is a high-power module with integrated uFl antennas that enables IEEE802.15.4 or ZigBee-compliant systems to be implemented at the lowest cost in the shortest amount of time. The surface mount module utilizes Jennic's JN5139 wireless microcontroller to provide a complete RF and RF device solution. The module provides the rich peripherals needed to develop a wireless sensor network. Module features: integrated uFl antenna slot; compatible with 2.4 GHz, IEEE802.15.4 and ZigBee protocols; 2.7 V~3.6 V operating voltage; sleep current (including sleep timer active) 2.8 μA; receiving sensitivity -100 dBm. MCU characteristics : 16 MHz 32 bit RISC CPU; 96 KB RAM, 192 KB ROM; 4 input ports, 12 bit ADC, 2 11 bit DACs, 2 comparators, 2 application level timers/counters, 2 serial ports (one For system online debugging), 1 SPI interface, support 5 chip selects. Ability to build robust, secure, low-power wireless networking applications.
3.2 Sensor and Conditioning Circuit Module
The design schematic diagram of the battery current and voltage detection circuit is shown in Figure 2. The current detecting circuit is composed of a Hall current sensor TBC10SY and a sampling resistor, a level adjusting circuit, a follower circuit, a filter circuit, and the like; the voltage detecting circuit is composed of a sampling circuit, a follower circuit, a filter circuit, and the like. It should be noted that the charging current and the discharging current are opposite in direction in the current detecting circuit, and the negative voltage value needs to be converted into a positive value by the voltage boosting circuit and processed in the program.
The design schematic diagram of the photovoltaic cell current and voltage detection circuit is shown in Figure 3. [4]. The signal on the precision small resistor of the photovoltaic cell power supply circuit is used as the current detection signal, and the differential amplifier circuit is fabricated by using the integrated operational amplifier ICL7650. Minimize the impact on the circuit under test. A small signal is incorporated into the large-resistance voltage divider of the photovoltaic cell as a voltage signal, and a differential amplifier circuit is also fabricated using the integrated operational amplifier ICL7650. In order to eliminate the interference, two equal-value resistors are respectively connected between the two input terminals of the amplifier and the ground, and a filter circuit is added at the output end of the amplifier, and the filtered current and voltage signals are output to the A/D of the controller JN5139. Conversion interface.
The LED lamp head illumination detection circuit is shown in Figure 4. Illumination detection uses the On9658 integrated sensor. The signal obtained by the sensor is amplified and filtered by the amplifier and output to the A/D conversion interface of the controller JN5139.
The LED lamp temperature detection circuit is shown in Figure 5. The battery temperature is based on the SHT11 integrated temperature sensor.
4 sensor node software design
4.1 Overall design of the software system
The main functions of the software system include sensor data acquisition and processing, wireless transceiver and node positioning, etc., and adopt modular design. The sensor data acquisition and processing module mainly sets the acquisition parameters of the battery status signal and controls the acquisition; the wireless transceiver module controls the reception and transmission of the command or data by setting the register; the node positioning module performs real-time positioning on the node. The sensor node is designed as a full-featured device (FFD) with routing function. The program flow chart is shown in Figure 6. The main task is added to the task queue for data acquisition, alarm detection and self-energy detection and the ZigBee transmission task is called. When the JN5139 pin interrupt is generated, the CPU goes to execute the ZigBee reception interrupt service routine. If it is an acquisition command, data collection and transmission are performed immediately; if it is a routing packet, the routing update is performed immediately.
4.2 Node Positioning Algorithm Design [5]
The node uses precise positioning based on the received signal strength indication positioning algorithm. Knowing the transmit signal strength of the transmitting node, the receiving node calculates the propagation loss of the signal according to the strength of the received signal, then converts the transmission loss into a distance according to the signal propagation model formula, and then calculates the position of the unknown node by using the trilateration method. In the actual positioning, it is necessary to ensure that the unknown node is in the communication range of more than three reference nodes whose transmission signal strength and position coordinates are known, and the unknown node calculates the propagation loss of the signal according to the received signal strength, and then calculates the node position.
This paper introduces the design of high-precision solar LED street lamp state sensor node based on wireless sensor network. In the actual test process, the system runs stably, the measurement result is in line with reality, and the high-accuracy acquisition and wireless transmission of the signal are fully achieved. Better monitoring results. The system combines the advantages of low power consumption, low cost and many nodes in the wireless sensor network, and it will be more and more widely used in the solution of key problems such as long-distance and high reliability of wireless communication technology.
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