DIY Humidity & Temperature IoT Sensor Node

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Learn how to create a humidity and temperature IoT sensor node with Sub-1 GHz connectivity for home & building automation 

Many industrial, building automation, and IoT systems require increasing numbers of wireless sensor end nodes. However, one of the major design constraints is that typical sensor end-nodes are powered by batteries, which should last from several months to several years depending on the power consumption of the end node. Replacing batteries can be a very expensive system-level cost, because each end node requires a periodic manual battery replacement. Here we discuss a sensor to cloud end node reference design from TI that addresses these challenges and enables a long battery life.

Humidity and Temperature Sensor Node With Sub-1 GHz connectivity

Humidity and temperature are both common measurements required for many end-equipment systems in industrial and building automation applications. For example, home heating and cooling systems are likely to include humidity and temperature measurements in each individual room. With the wireless functionality of the system, this environmental information is sent back to a smart thermostat, to provide a much more intelligent home environment by providing individual comfort settings in different rooms and increasing energy savings. Also, in cold-chain logistics, temperatures must be controlled at all times during shipping to prevent product deterioration.

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The reference design discussed here is powered by a coin cell battery and capable of connecting to an IoT network gateway and cloud data provider. Temperature and humidity data is collected and transmitted every five minutes to the sensor-to-cloud gateway. The design consists of a CR2032 coin cell battery, a nano-power system timer, a low IQ boost converter, an ultra-low power wireless MCU, and a combined humidity and temperature sensor.

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Key design considerations are discussed below:-

Ultra-low-power wireless MCU

With TI’s SimpleLink ultra-low-power wireless MCU platform, low power with a combined radio and MCU enables extremely long battery life for sensor end-nodes.

HDC2010 humidity and temperature sensor

With a relative humidity accuracy of ±2% and a temperature accuracy of ±0.2°C, the HDC2010 device from Texas Instruments is ideally suited to accurately sense environmental information. The innovative placement of the HDC2010 sensing element on the bottom of the device provides resistance to dust, dirt, and other environmental contaminants, which improves system reliability for applications like heating, ventilation, and air conditioning (HVAC) systems, smart thermostats, and room monitors.

The Function of a Nano-Timer

It’s really important to minimize power consumption during the sleep phase, where the node spends the vast majority of its time. A nano-timer can play an important role in minimizing sleep current and managing the go-to-sleep and wakeup phases of a battery-powered IoT node. This device increases battery life by replacing the internal timer of the MCU with an analog device that consumes much less power. A nano-power system timer can wake up the MCU with an interrupt, or initiate sleep mode by completely shutting off power to the system.

This design uses the TPL5110 nano-timer that manages the wakeup and shutdown of a battery-powered IoT node by controlling the MCU power supply.

Key features of the design

• Large Network-to-Cloud Connectivity Enabling Long Range, Up to 1 km (Line of Sight)
• IEEE 802.15.4e/g Standards-Based Sub-1 GHz Solution With TI 15.4-Stack
• Configurable System Wakeup Interval
• Low Standby Current (1 µA)
• ±2% Relative Humidity Accuracy
• ±0.2°C Temperature Accuracy

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Applications

• Wireless Environmental Sensor
• Thermostat
• Smoke and Heat Detector
• Air Quality and Gas Detection
• Building Automation

Click here for reference design

 

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