Easy Very Low Power BLE in Arduino Part 2 -- Temperature/Humidity Monitor

This tutorial is a practical application of Part 1 Building Very Low Power BLE devices made Easy with Arduino by constructing a Very Low Power BLE Temperature and Humidity Monitor. The monitor will run for years on Coin Cell or 2 x AAA batteries, even longer with solar assist. This tutorial covers tuning the BLE parameters for low power consumption and how to power you device from battery OR battery + solar OR solar only.

As well as displaying the current temperature and humidity, the monitor stores the last 36 Hrs of 10min readings and the last 10 days of hourly readings. These can be charted on the your Android mobile and the values saved to a log file. No Android Programming is required, pfodApp handles all of that. The Android display and charting is completely controlled by your Arduino sketch so you can customize it as required.

A Redbear Nano V2 board is used for the nRF52832 BLE component and a Sparkfun Si7021 breakout board is used for the Temperature / Humidity Sensor. A modified low power library is used with the Si7021. A small PCB was designed to hold the NanoV2 and supply components. However since there are no surface mounted components used, you can just as easily build this on vero board. Three power supply versions are covered. i) Battery plus Solar assist, ii) Battery Only, iii) Solar Only. The Solar Only option does not have any battery storage and so will only run when there is some light. A bright room light or desk lamp is sufficient.

Outline
This project has 4 relative independent parts:-

Component Selection and Construction
Code – Low Power Sensor Library, User Interface and Arduino Sketch
Measuring Supply Current and Battery Life
Supply Alternatives – Solar Assist, Battery Only, Solar Only”

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