Introduction
WSN (Wireless Sensor Network) is a multi-hop-based self-organizing network that is sent to the observer by deploying a large number of miniature sensor nodes, collaboration, collecting, acquisition, and processing network coverage areas in the monitoring area. WSN Technology is listed as one of the most influential 21 technologies in the 21st century and the world's top 10 technologies in the 21st century. WSN has broad application prospects in military, civil and industrial and commercial fields. Through WSN, in the military field, the information obtained on the battlefield can be quickly transmitted back to the headquarters; in the civilian field, it can be applied to smart home, environmental monitoring, health care disaster prediction, etc .; in the industry and commerce, applied to industrial automation and Space exploration, etc. WSN is a major research hotspot in the field of domestic and foreign communications.
In WSN, sensor nodes are the most basic unit in the network, which is the basis of the WSN. Sensor nodes are typically composed of sensor units, processor units, wireless communication units, and power supply unit 4. The sensor node uses the battery and the node energy is limited, and its data processing capability, storage capacity, and node communication capabilities are also limited. Therefore, the quality of sensor node design will directly affect the stability of the network. According to the above characteristics, this paper uses the CC1110 chip design WSN node, and the design results meet the characteristics requirements.
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1. Introduction to CC111O chip
The CC1110 chip is a low-power RF (RF) SOC (SMS) solution of 1 GHz below the US TI. The chip is made of CHIPCON SMART RF 04 technology, which is made of 0.18 μmcmos process, and only the very few external components can constitute a SOC that is stable and low power consumption.
The CC1110 chip has a working voltage of 2.0 V to 3.6 V and has a rich peripheral interface. There are 21 GPIOs, 2 USART interfaces and programmable watchdog timers, with 1 16-bit timer, 3 8-bit timers, and random number generators; embedded 128-bit AES security coprocessors and Powerful DMA function, etc. In RF performance, high sensitivity (-110 dBm at a rate of 1.2 kbaud) and a higher reception sensitivity and blocking function; support 2-fsk, GFSK, and MSK, the frequency range is 300. MHz ~ 348 MHz, 391 MHz ~ 464 MHz and 782 MHz ~ 928 MHz; support digital RSSI / LQI; maximum output power can reach 10 dBm, maximum data rate can reach 500 kbaud.
In summary, the CC1110 has high integrated degrees and low power consumption, in the QLP package of 6 mm × 6 mm, integrated CC1101 RF transceiver, enhanced 8051 microcontroller, 8/16/32 kb flash memory and 1/2 / 4 KB RAM and other powerful features; there are 4 power management models, switching from low-power status to work status very fast. Therefore, it is suitable for the alarm and safety, automatic reading, industrial monitoring, and building automation. It is possible to meet the requirements of WSN's service life, size, cost, and product development time.
2, node hardware design
The CC1110 chip can make a SOC that is stable and reliable and low, which is capable of constructing a very small number of peripheral components, greatly simplifies the design process of the RF circuit. Designed sensor nodes working in 433 MHz band. 2 is a reference design of CC1110, which is mainly composed of a CC1110 chip, a radio frequency matching circuit, and other peripheral components.
The RF matching circuit is used to match the chip input, the output impedance, the input, the output impedance is 50 Ω, and the PA (power amplifier) and LNA (low noise amplifier) inside the chip provide DC bias. The impedance matching circuit uses the BALUN circuit, composed of L232, L242, C234, and C241. The RF signal of the CC1110 uses a differential mode in a 433 MHz band, its optimum differential impedance is 116 + J41 Ω.
The RF section circuit design refers to the typical design of Figure 2, but a small amount of modification is carried out in the circuit, and PA is added. According to the actual application environment, the node can work in two states of PA, no PA, such as Coordi-Nator, and the Range Extender two nodes can be operated in the way PA (generally adopting the main transmission) to achieve long-distance transmission. The sensor node in which the design is designed is shown in Figure 3.
The sensor module of the node uses the full calibration digital temperature and humidity sensor SHT71 based on SENSITION technology based on Switzerland. On a chip, a temperature and humidity sensor, a signal amplifying adjuster, a / D converter, and a bus interface can provide temperature measurement of 14 bits in the range of 14 bits and 0 to 100% in the range of 14 bits. Humidity measurement of the resolution is 12 bits. The SHT71 is connected to the CC1110 with the serial interface. Its serial clock input line SCK and serial data line DATA are connected directly to the GPIO port line of CC1110, and the circuit connection is shown in Figure 4.
3, node software design
The software design of the node mainly includes a temperature and humidity acquisition portion and a wireless data communication section.
3.1 Temperature and humidity collection
The temperature and humidity sensor SHT71 is synchronized with the CC1110 via SCK, and the communication protocol command and data are sent and received through the DATA line. The control flow is as follows: The CC1110 sends a set of "start transfer" timing for data transmission initialization, then sends a set of measurement commands, release the DATA line, waiting for the SHT71 drop down DATA line to the low level, indicating the end of the measurement, and receives data. After the CC1110 receives the measured value, the temperature T and the relative humidity H can be calculated according to the following formula:
Where: coefficients D1, D2, C1, C2 and C3 can be found in the relevant manual.
3.2 Wireless Data Communication
The following is an example of node point-to-point communication, introducing communication implementation methods and communication processes between wireless sensor nodes. The MAC frame structure of the CC1110 is simple, eliminated the leading code and synchronization word of the physical layer, only one optional length byte n, an optional address byte, user data, and two optional CRC bytes, as shown 5 shown.
In order to facilitate the data processing during communication, the following data transmission and reception processing structure is defined:
Wherein, the flag flag is 1 byte, used to represent the type of the current data frame. When the 0th bit of the Flags byte in the flags byte is 1, indicating that the target node does not need Ack after receiving the data frame; the first bit is 1, indicating that the target node is Ack after receiving the data frame; When the 2 bits are 1, the frame is an ACK frame; the third bit is 1, indicating that the frame is a timeout reconciliation frame; the highest bit is 1, indicating that the frame is one frame in the data sequence.
The communication RF setting of the sensor node is then explained. When the node is used, the crystal frequency is 26 MHz, RF initialization, sets the register FREQ2, FREQ1, and FREQ0, configuring the operating frequency of the physical layer of RF; sets the communication channel by the CHAN bit field of the register CHANNR; set the register MDMCFG0 The CHANSPC_E bit field of the CHANSPC_M bit field and register MDMCFG1 is set to set the channel interval. The specific carrier frequency fc can be represented by the following formula:
Where: FREF is 26 MHz, the maximum channel interval is 405 kHz. Of course, these register settings can be calculated via Ti's software Smartrf Studio.
The RF module is implemented with Memory data accesses through the DMA mode in the DMA mode, without CPU intervention. The data structure described in the DMA channel is as follows:
Take the transmission as an example, explain the DMA configuration process and the meaning of each structure member.
When sending, the source address SRCADDRH and SRCADDRL of the data are first set to the start address of the register, the target address DestAddrh, and DestAddrl set to the register RFD.
Then, in the length of the Lenh and Lenl bit field setting, the VLEN bit field is set to 0; set the WordSize bit field to 0, let DMA only transmit 1 byte again; set the TMODE bit field to 0 (Single mode The DMA data transfer mode can be divided into four), that is, during the data transfer process, once the DMA trigger can perform a WordSize transmission. Configure the TRIG bit field to RF trigger mode (31 of the DMA trigger signal); the CSRCINC bit field and the DES-TINC bit domain are used to set the data source address and the target address, and can be set to constant, increase 1, Increase 2 or minus 1. In this example, the data source address is selected to increase, and the data target address is set to constant (only the RFD register); the IrqMask bit domain bit is used to set the interrupt signal after the DMA data transmission is completed, and this example is forbidden from disrupting DMA interrupt; The M8 bit field is a data width at byte transmission, set to 0 indicates an 8-bit transmission, indicating a low 7 bits that only transmit bytes, and set the Priority bit field to low priority.
4, experimental results
The sensor node adopts modular design, compact structure, small size. The design of the CC1110 sensor node performs single-package transmission, continuous transmission, and point-to-point pair test when the communication frequency is 433 MHz and the modulation method is 2-fsk, and performs a bit error rate test. The experimental results are ideal, and the empty environment communication distance reaches around 1 km, and the error rate is about 1%. In the power amplification test, the node output power with the PA function reaches 25 dBm, which is well satisfied with design performance.
5, conclude
This paper describes the design and implementation of the wireless sensor node based on CC1110. The node can collect the temperature and humidity of the field environment and go to the upper network node. The research work in this paper provides a good hardware foundation for further research wireless sensor communication protocols. The results also show that the implementation of the CC1110 as the core of the sensor node provides a solution for WSN, with strong application value.
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Reprinted from -Wiku Electronic Market Network
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