In today's industrial and agricultural production, there is a need for temperature and humidity collected, and more accurate and convenient measurement temperature is critical. The traditional wired temperature measurement is complex, the line is easy to aging, the line fault is difficult to investigate, and the equipment is re-laying to rearrange. Especially in the case where the wired network is not smooth or the line is not allowed to set the line, the data collection of temperature and humidity has brought a lot of trouble. To monitor the real-time temperature and humidity data, you must collect, send, receive and receive data on the wireless transmission, and process the wireless acquisition to control and monitor the operation of the device, reduce unnecessary Line equipment expenses.
Temperature and humidity acquisition circuit design
It is a temperature and humidity composite sensor that has been calibrated digital signal output. The sensor application dedicated digital module collection technology and temperature and humidity sensing technology have extremely high reliability and excellent long-term stability. Figure 2 shows its temperature acquisition circuit. The sensor includes a resistive moisture absorbent element and an NTC temperature measuring element that is coupled to a high performance 8-bit microcontroller. The calibration factor is stored in OTP memory in the form of a program, and these calibration coefficients can be called during the detection signal. Single-wire serial interface allows system integration to become simple and fast, and signal transmission distance can reach 20m or more. When the cable length is shorter than 20 m, a 5kΩ pull-up resistor should be used, when it is greater than 20 m, the appropriate pull-up resistor should be used according to the situation.
Wireless transmission, receiving circuit design
NRF24L01 is a wireless communication chip produced by Nordic, using FSK modulation, and internal integration with Nordic's own Enhanced Short Burst protocol. Point-to-point or 1 to 6 wireless communication can be implemented. The wireless communication speed can reach 2 MB / SORDIC wireless transmission, and the circuit schematic diagram of the receiving chip NRF24L01 is shown in FIG.
NRF24L01 is a single-chip radio frequency transceiver chip, a functional module such as an ISM band of 2.4 to 2.5 GHz, a chip built-in frequency synthesizer, a power amplifier, a crystal oscillator, and a modulator, an output power, and a communication channel to be configured by a program. When the NRF24L01 chip is very low, the working current is only 10.5 mA when the power is transmitted, and the working current is only 18 mA, which has a variety of low-power working modes, energy saving and environmental protection, convenient design. The respective pin functions of the NRF24L01 wireless transceiver module are listed in Table 1, and FIG. 4 is a circuit diagram when the NRF24L01 is connected to the microcontroller.
The power supply required for this wireless transmitting receiving module is 1.9 ~ 3.6 V, and the 3.3 V DC power supply is used to power the wireless transmitting receiving module directly, 5 V power supply. A stable DC power supply after the ASM1117-3.3 chip is converted, and the power conversion circuit is shown in Figure 5.
Serial communication module
After the host microcontroller receives the data of the NRF24L01, the MAX232 level conversion can realize the microcontroller program to download and upgrade, and the communication of the microcontroller and the PC (host computer) can be realized to transmit the display data information to the PC, computers The PC is displayed on the serial communication circuit as shown in Figure 6.
This paper proposes a solution for wireless data transmission issues, which is based on NRF24L01 to design a wireless temperature acquisition system. The system uses low-power, high-performance microcontroller STC12C5A08S2 and temperature and humidity sensors to constitute multi-point, real-time temperature and humidity monitoring system, and finally completed configuration, display, and alarms on the PC. The system is easy to use, and it is very easy to expand, which can be widely used in various industrial and agricultural production and farming.
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