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Wireless bi-directional data link for smart temperature recording

In application systems of the Internet of Things (IoT), real-time monitoring and control of the systems need to be realized with wireless communications from machine to machine (M2M), especially under harsh application scenarios. The data link of the M2M communication has also a critical effect on the system in the application. In this paper, a wireless bi-directional data link for smart temperature recording is reported. The radio frequency hardware employed consists of NRF24L01 wireless transceivers, RFX2401 amplifiers and matching network sand antennas. The microcontroller unit (MCU) is based on the STM32F103VET6 chip, which controls the NRF24L01 by a four-pin serial peripheral interface (SPI) to realize the bi-directional data link, and the sensor data are sampled with 12-bit analogue-to-digital converters (ADCs). The communication is realized as the interrupt request (IRQ) signal of the NRF24L01 changes periodically. A look-up table and a linear optimization method are also implemented to improve the accuracy of ADC data. The bi-directional data link is then applied to a wired heating control system. The results show that temperature data can be transmitted and received over a distance up to 320 m in an open environment and 52 m in an indoor complex environment with the hardware implemented. The real-time temperature data can be displayed on a computer or a handheld device. Wireless M2M communication and control are thus demonstrated.