Design and implementation of a low-power wireless sensor network using power-saving techniques

A wireless sensor network (WSN) is a significant technological element of the Internet of Things (IoT). The core of a WSN consists of wireless sensor nodes (IoT nodes) that collect and transmit data from the installation sites to digital platforms. As IoT applications expand into various environments, the demand for low-power IoT nodes is becoming increasingly important. In this paper, we propose the schematic and implementation of low-power IoT nodes using power-saving techniques on the low-cost ESP8266 module. The IoT node contains the ESP8266 module and sensors to collect environmental data, including temperature and humidity then transmit via the ESP-NOW protocol. The ESP8266 module fully integrates both a Wi-Fi transceiver and a microcontroller, which contains central processing unit (CPU), system clock (SYC), and real-time clock (RTC) on a compact chip. However, in active mode, both the Wi-Fi transceiver and microcontroller are enabled, so the power consumption of the ESP8266 module is comparatively elevated, even when the Wi-Fi transceiver is in a state of waiting to receive or transmit data. To reduce power consumption, power-saving techniques of applying the sleep mode of the ESP8266 module was proposed in the design. Three sleep modes, including modem-sleep, light-sleep, and deep-sleep are provided by the ESP8266 module. Each sleep mode configures components such as the Wi-Fi transceiver, CPU, SYC, and RTC to be on or off differently. The IoT node was also programmed with the function of switching between sleep modes, from which users can select and configure the sleep mode and sleep duration accordingly. The power consumption of the IoT nodes is analyzed and evaluated between three sleep modes based on sleep duration and events. These IoT nodes are deployed in real-world environments to monitor various environmental conditions.