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Designing Sensors into Battery-Powered IoT Nodes

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Introduction

The Internet of Things (IoT) is turning real-world “analog” events into networked actions and reactions. Connected IoT nodes monitor analog events and, when events occur that need to be reported, translate them over the Internet to the cloud for an application to do something with it.

One of the most prominent classes of IoT applications uses battery-powered sensors, placed in a zone with no electrical wires to monitor events and communicate wirelessly to the IoT network. In most cases, these products are always-on, battery-operated, wireless sensors that support a wireless protocol, an MCU, and at least one analog sensor.

The challenge is to maximize the time the product can adequately sense the environment on a single battery or charge. This challenge breaks down as follows:

1. Adequately sensing the environment as required by the application;

2. Completing any required sensor measurements using as little energy as possible;

3. Keeping the “periodically required” MCU peripherals and CPU core asleep as much as possible.

 

Many typical MCUs in this type of application wake up the MCU core and various peripherals to do sensor measurements (Figure 1). When there is an event to report, such as a door opening, the MCU reports it and then returns to its duty-cycle process. This takes a lot of energy and does not maximize battery life because the “whole MCU” is operating including many peripherals and unneeded core processing power.

In fact, this approach will most likely result in a poor customer experience: the customer puts the device into their environment, sets it up on the network, and enables it, only to have it die a few months later because it does a poor job of managing its battery power.

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Figure 1: High energy consumption with CPU polling and active during every measurement.

 

The Ideal Battery-Powered, Wireless Sensor Node Solution for the IoT

The ideal solution will address every point in the challenge statement above… it will maximize the time the product can adequately sense the environment on a single battery charge.

With this in mind, a battery-powered IoT sensor device would offer:

1. Autonomous, energy-efficient systems for sensor management and measurement;

2. Individually configurable sensor inputs/outputs, thresholds, and configurations for each sensor;

3. A low-power, configurable logic engine that wakes up the MCU only when it’s absolutely required;

4. Low-power memory to buffer multiple measurements and lengthen times between CPU wake-ups; 5. Low-power wireless.

 

Download and read the complete white paper here.