Abstract
The development of energy and cost efficient IoT nodes is very important for the successful deployment of IoT solutions across various application domains. This paper presents energy models, which will enable the estimation of battery life, for both time-based and event-based low-cost IoT monitoring nodes. These nodes are based on the low-cost ESP8266 (ESP) modules which integrate both transceiver and microcontroller on a single small-size chip and only cost about $2. The active/sleep energy saving approach was used in the design of the IoT monitoring nodes because the power consumption of ESP modules is relatively high and often impacts negatively on the cost of operating the nodes. A low energy application layer protocol, that is, Message Queue Telemetry Transport (MQTT) was also employed for energy efficient wireless data transport. The finite automata theory was used to model the various states and behavior of the ESP modules used in IoT monitoring applications. The applicability of the models presented was tested in real life application scenarios and results are presented. In a temperature and humidity monitoring node, for example, the model shows a significant reduction in average current consumption from 70.89 mA to 0.58 mA for sleep durations of 0 and 30 minutes, respectively. The battery life of batteries rated in mAh can therefore be easily calculated from the current consumption figures.
Highlights
This paper presents energy models, which will enable the estimation of battery life, for both time-based and event-based low-cost Internet of Things (IoT) monitoring nodes
The active/sleep energy saving approach was used in the design of the IoT monitoring nodes because the power consumption of ESP modules is relatively high and often impacts negatively on the cost of operating the nodes
Since IoT monitoring nodes are mostly powered from small battery sources and the capacity of these battery sources are rated in mAh which is a unit of electric charge (Q) and indicates the amount of current that a battery can continue to supply for one hour, the energy model proposed in this work focuses on the current consumption of IoT node components
Summary
An ESP8266-12E module, for example, consumes an average of 70.5 mA when it is fully on (that is, when its WiFi modem and microcontroller are both on) even when the transceiver is inactive (neither receiving nor transmitting). The deep-sleep mode is the primary target for most low energy monitoring applications In this mode, the WiFi modem, system clock and CPU are all switched off while only the real time clock (RTC) is left on to enable user-defined periodic wake-ups. The focus of this work is on the development of power consumption models that will enable IoT solution developers to determine approximately how long a power source (of known mAh capacity) will continue to power an ESP8266-enabled IoT time- and event-based monitoring node before it will require a replacement or recharge.
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