ZigBee - New Low Power Wireless Standard

ZigBee - new low power wireless standard

More and more wired data transmission is being replaced by wireless solutions. For users, the abandonment of cables not only brings more convenience, but also greatly reduces the installation cost. Especially in sensor networks and control applications, the installation and transformation cost of existing networks is an important consideration. When switching from a wired network to a wireless network, usually the node also needs to switch from wired power supply to battery power supply. In wireless networks, the power consumption of each node becomes an important factor. Therefore, ultra-low power design technology becomes very important, especially when wireless sensor nodes use only one battery for many years.

If you decide to use wireless network, the first step is to select existing wireless standards or implement proprietary solutions, and complete comprehensive system development internally. Both approaches have advantages and disadvantages:

*Proprietary solutions

O advantages: high hardware flexibility and low cost, because only necessary functions need to be realized.

O disadvantages: the software stack and transport protocol take a long time to develop and are incompatible with other devices

*Standard solutions

O advantages: short development time because there is an existing software stack and has been tested by multiple users. Compatible with products of other manufacturers.

O disadvantages: generally, the standard software part is not necessary and is not used in the application. This increases the memory capacity required for software and data storage.

There are many widely recognized wireless standards, and each one is specific to a specific application field. For example, the familiar wi FI / 802.11 and Bluetooth RF standards, the former is suitable for high-speed transmission with relatively short distance and medium power consumption. It can be used for PC networking, home networking and video distribution; The latter has low power consumption, short distance and medium speed transmission. It can be used for headset, PC peripherals, PDA and mobile phone connection.

In most control applications, these standards are not ideal. For example, for sensor networks, ultra-low power consumption, which can make devices work for many years with a small battery, is the key. A high data rate is not necessary because only a few control commands and some measurements need to be transmitted.

IEEE 802.15.4 - Fundamentals of ZigBee

Therefore, Wi Fi / 802.11 and Bluetooth are not the best solutions for sensor and control applications. For this reason, the industry developed the IEEE 802.15.4 standard and launched it in October 2003. In June 2006, IEEE 802.15.4-2006 (Rev b) was approved. The standard not only describes point-to-point transmission in personal area network (Pan), but also defines phy and MAC layers for low power consumption, low speed and reliable RF transmission. Generally, the transmission distance indoors ranges from 10 to 30 meters, and the maximum transmission distance outdoors can reach 150 meters. Depending on the specific application, the battery life can be up to several years.

Figure 1 global distribution of free frequency bands

Before implementing wireless transmission, it is also necessary to define the transmission frequency. Figure 1 shows the distribution of global frequencies today. Frequencies below 1GHz are used differently in different regions of the world. In Europe, 433MHz and 868mhz are free, while in the United States, 315MHz and 915MHz are free. Only 2.4GHz band (Wi Fi and Bluetooth also use this band) it is free to use around the world. In addition, the same antenna can be used for 868mhz and 915MHz. As long as there is a flexible and freely programmable RF transceiver, a global solution that can optionally run on 868mhz or 915MHz is also a good choice. In this case, it is necessary to ensure that the operating frequency is converted to the operating frequency of the device The band range allowed by the line region. This will increase the cost because two different firmware versions must be released.

IEEE 802.15.4 is specifically defined for the following frequencies:

*868mhz, 1-channel 20kbps... 100kbps (Europe only)

*915MHz, 10 channel 40kbps... 250kbps (USA only)

*2.4GHz, 16 channel 250kbps (applicable to all regions of the world)

ZigBee -- software stack

ZigBee alliance is an industry association composed of many companies. These companies work together to achieve reliable, low-cost, low-power, wireless network monitoring and launch control products based on open global standards. The promoters of ZigBee alliance include BM spa, ember, Freescale, Honeywell, Huawei, Mitsubishi Electric, Motorola, Philips, Samsung and Schneider Gas, STMicroelectronics, Siemens, Ti and other companies. The alliance has more than 200 members, and this number is growing. The alliance defines ZigBee stack: a standard protocol stack based on IEEE 802.15.4 phy and MAC. The target application fields of ZigBee are as follows:

*Home automation:

O automatic meter reading (AMR)

O lighting, heating, alarm, safety

O white appliance health status monitoring

*Commercial building automation

O heating, ventilation and air conditioning system (HVAC)

O energy management

O alarm, safety

*Industrial automation

*Hospitalization and patient care

*Asset tracking / active RFID

*Wireless Sensor Networks

Figure 2 ZigBee star network

Figure 3 ZigBee mesh network

The ZigBee stack over IEEE 802.15.4 point-to-point communication protocol makes it possible to implement the personal area network (Pan) of ZigBee nodes. Star network topology (see Figure 2), tree or mesh network topology can be adopted (see Figure 3). Each ZigBee pan requires a pan coordinator device. The pan coordinator starts the network and assigns a pan-id to the new network. In addition, the pan coordinator usually has packet routing function. In tree and mesh networks, there are usually several nodes with ZigBee router function. These router nodes can forward the received packets to the next network ZigBee nodes, and through the complete ZigBee network, the jump of data packets from sender to receiver is realized in this way.

ZigBee terminal devices only communicate with their parent nodes (Pan coordinators or routers). These terminal devices have relatively few functions because they do not require routing functions. Reduced function devices (RFDS) One advantage of RFD is that the stack size is significantly smaller. Therefore, the requirements for program flash memory, data memory RAM and flash memory are greatly reduced. This makes RFD, which is usually the main part of ZigBee nodes, a cost advantage. RFD is especially suitable for ultra-low consumption design, because microcontrollers and RF transceivers can be turned off most of the time. It is a device with routing function Always remember that it must receive a packet.

ZigBee uses 16 bit node addressing, which theoretically allows nearly 2 ^ 16 ZigBee nodes in a pan. In practical applications, the number of nodes is limited by packet delay. For star networks,

get in touch with us
recommended articles
General Intelligent Wireless Transceiver Based on NRF401
General intelligent wireless transceiver based on nRF401At present, wireless data transmission devices need to be embedded in various instrument data acquisition systems and remote control measurement and control systems. This paper introduces a design method of general wireless transceiver that intelligently controls the wireless transceiver chip nRF401 through single chip microcomputer W77E58. The design of hardware circuit is divided into two parts: the design of wireless RF module and the design of control module. The serial port of the device can be selected as RS232 standard or TTL level standard through jumper device. Dual channel switching and data flow control can be realized through W77E58 control.1 design of radio frequency moduleIn this design, the wireless RF module adopts nRF401 wireless transceiver chip launched by Nordic company in Norway. The chip uses 433 MHz ISM frequency band and is a real single-chip UHF wireless transceiver integrated chip. It includes high-frequency transmission, high-frequency reception, PLL Synthesis, FSK modulation, FSK demodulation, multi-channel switching, etc. in a 20 pin chip, it is the most integrated wireless data transmission product at present [1]. The radio frequency module adopts on-board differential ring antenna, and the load impedance of the antenna port is 380 ω, The circuit principle is shown in Figure 1, which lists the parameters of each peripheral element, in which J1 port is the interface between radio frequency module and control module.The key points of hardware circuit design are as follows:(1) RF circuit is quite sensitive to power supply noise. Star wiring must be adopted to make the digital part and RF part have their own power lines, and they should be decoupled near the power pin of the integrated circuit [2].(2) The external VCO electric induction adopts the high-frequency inductor, Q > 45, with an accuracy of 2%. This design adopts the lqw18an22ng00 of Shenzhen shunbai Technology Co., Ltd. the accuracy of the inductor has a great impact on the wireless communication distance. It can also use the inductor with an accuracy of 5%, but the communication distance will be greatly reduced. VCO inductance wiring shall be kept at a certain distance from other control lines, and digital control lines shall be avoided from passing between inductance pins. The center distance of VCO inductance components shall be about 5.4mm from the center of VCO1 and VCO2 pin pad of nRF401. The selection and layout of inductance components are very important and the key point of design success or failure.(3) A large area of copper laying shall be used on both sides of the circuit board as the grounding ground, so that all devices can be easily decoupled. The copper laying on both sides shall be connected by multiple vias. All connections to the ground wire layer must be as short as possible, and the grounding vias shall be placed at the pad very close to the components [2].(4) The antenna is designed with a ring antenna of PCB board, with a size of 35mm × 20mm, antenna gain: - 11db, antenna impedance 380 ω, The antenna shall be located on the top of the PCB board, and the antenna part shall not be covered with copper. For the design of the ring antenna, please refer to the technical documents nan440-03 and nan400-05 of Nordic company.(5) If the VCO inductance of the PCB board is designed reasonably, when the module is in the receiving state, the voltage of the fourth pin of nRF401 is 1.1 ± 0.2V.2 design of control moduleThe control module is responsible for the control of radio frequency module state switching and channel switching. Huabang single chip microcomputer W77E58 is selected. The design of the control module is divided into two parts: hardware circuit design and software design.2.1 design of hardware circuitW77E58 has high speed and can be extended to 40MHz. It uses the same crystal oscillator as 8051 / 52, and its running time is 2.5 times faster than 8052 [3]. It is equipped with two UART serial ports. Serial port 0 is used to communicate with external serial port equipment, and serial port 1 is used to communicate with wireless transceiver module. Port J6 is the interface between control module and wireless RF module, and port J2 is the interface between control module and external serial port equipment, The simple three wire communication mode can be adopted, and the flow control signal CTS can also be added. The reset pin can be controlled by TTL level to reset the intelligent wireless data transmission module. J2 port and external serial port equipment can communicate in the form of RS232 or TTL level. The communication form is selected by setting the jumpers of interfaces J3, J4 and J5. MAX232 and peripheral capacitor elements can adopt patch devices to reduce the space of PCB board. Through p2.5, p2.6 and p2.7, the switching of standby state and working state, transceiver state and channel of radio frequency module are controlled respectively.2.2 software designW77E58 chip is equipped with two serial ports, in which serial port 0 can use timer T1 or timer T2 as baud rate generator; Serial port 1 can only use timer T1 as its baud rate generator [4]. In this design, T2 is used as the baud rate generator of serial port 0 and T1 is used as the baud rate generator of serial port 1. Both serial ports work in serial port mode 1 with a baud rate of 9600b / s. serial port 0 occupies the 4th interrupt, and scon and SBUF are used as its serial port control register and serial port data buffer; Serial port 1 occupies interrupt No. 7. Scon1 and sbuf1 are used as its serial port control register and serial port data buffer. The initialization function for the serial port is init_ The serialport() function is defined as follows:In the process of wireless communication, due to the interference of the external environment, the bit error rate is usually high. Even if the transmitter does not send data, the receiver will often receive the disordered data caused by external interference. In order to distinguish whether the received data is valid data in the process of receiving, there must be a certain communication protocol:(1) The data transmission of the two serial ports adopts the query mode, and the data reception adopts the interrupt mode;(2) The data frame includes two parts: frame header and data. The frame header uses double byte 0x55aa, and the data part is 1b, that is, each frame occupies 3B. The frame header and data part are transmitted by hexadecimal ASCII code to ensure the transparency of the protocol;(3) If the receiver receives 0x55 0XAA bytes, it indicates that a valid data frame has been received. Otherwise, the frame will be discarded.If the hardware circuit design is reasonable, the selection of components is appropriate, and the above simple communication protocol is added, the bit error rate can be controlled below 0.2%.After the single chip microcomputer is powered on, the system and serial port are initialized first, and then the single chip microcomputer enters the standby mode until one of the two serial ports is interrupted, and the hard mode is changed to the working mode to process the interrupt program. The main program codes are as follows:3 hardware circuit testIn this design, the control module and radio frequency mode are designed separately. The control module controls the radio frequency module through a single row of 7-pin interface. The test steps are as follows:(1) Weld the control module and radio frequency module, and check and confirm that there is no false welding and sticking welding;(2) First, test the power on of the control module, mainly to test whether the serial port 0 and serial port 1 of the control module can send and receive data from each other. The test method is to set the serial port 0 to RS232 standard through the jumper on the board. Since the serial port 1 on the board has only TTL level standard, it must be converted to RS232 standard by adding a level conversion circuit, and then connect the two serial ports to the two serial ports of the computer respectively, Write the above program to W77E58, and then test it with serial port test software. If serial ports 0 and 1 can send and receive data from each other, you can start testing the radio frequency module;(3) Weld the J1 port of the radio frequency module with the J6 port of the control module, power on and test. According to the above procedures, it is in the receiving state when powered on, and test the TXEN, pwup, CS and other pins to see whether they are consistent with the procedures;(4) After confirming that the RF module is powered on and in the receiving state, test whether the fourth pin of nRF401 is about 1.1V. If so, it indicates that the VCO inductance design is reasonable, otherwise the PCB board needs to be redesigned. In addition, nRF401 will automatically send random data from dout when there is no data reception. When testing with a multimeter, the voltage of this pin should be about 2.5V [4]. If there is an oscilloscope, it can be tested in more detail.4 ConclusionAn intelligent control wireless transceiver is composed of wireless transceiver chip nRF401, single chip microcomputer W77E58 and interface chip max323. The device has universality and can be embedded in various instrument data acquisition systems and remote control and telemetry systems to realize two-way transmission of wireless data.
What Is the Role of Wireless Sensors in the Internet of Things
What Are Some Ways to Keep My Hair Really Healthy?
How Was the First Sale of Vivo X60 Series?
Huami Technology Held a Press Conference on August 27, and Amazfit Smart Sports Watch 3 Officially A
Connect to Nonencrypted Wireless Network Using Ubuntu Commands
Is Time Travel Possible? Can We Travel Back in Time?
Which Is a Better Design to Put on a Beer Pong Table?
What Else to Do on PS3?
How to Protect Data on IOT Devices
related searches
General Intelligent Wireless Transceiver Based on NRF401
What Is the Role of Wireless Sensors in the Internet of Things
What Are Some Ways to Keep My Hair Really Healthy?
How Was the First Sale of Vivo X60 Series?
Huami Technology Held a Press Conference on August 27, and Amazfit Smart Sports Watch 3 Officially A
Connect to Nonencrypted Wireless Network Using Ubuntu Commands
Is Time Travel Possible? Can We Travel Back in Time?
Which Is a Better Design to Put on a Beer Pong Table?
What Else to Do on PS3?

Copyright © 2020 Coffee bag - Guangzhou tianci packaging industry Co,. Ltd. | Sitemap