Home tracker environmental sensors

This repository contains the Arduino code for environmental sensors I'm developing.

I have discussed this project on my blog at statox.fr.

Software architecture and setup

~~The ATWINC1500 directory contains code for uploading to Adafruit Feather M0 WiFi boards~~
~~The ESP8266 directory contains code for uploading to Adafruit Feather Huzzah boards~~

~~Both directories contain board-specific versions of the same code for interfacing with the network, reading the battery level, starting deep sleep mode and running the main loop.~~

The project now uses only Adafruit Feather M0 WiFi boards to keep things simple. The code of the sketch is in the M0_SENSOR directory.

The libraries directory holds common code used by both board-specific projects and other dependencies.
- Statox_Blink is a utility for blinking the built-in LED of the boards.
- Statox_Sensors is my collection of wrappers around other libraries for reading various sensors (BME280, DHT11/22, SHT30, NTC-MF52 thermistors)
- Statox_Config contains configuration header files for the sensors I'm creating. (e.g. WiFi SSID and passwords) (Only *.sample.h files are versioned they must be copied to their equivalent without .sample in their name)
- The other directories are libraries installed via Arduino IDE. (TODO Find a better way to manage that?) I am not the author of these libraries their individual licenses should be respected.

The project is designed to be opened by Arduino IDE 2.x as a "Sketchbook"

Opening either of the board-specific sketches should open a new instance of the IDE
You may need to set the "Sketchbook location" setting to the root directory of this repository in "File > Preferences" in the IDE

Additionallly, you need to install the boards packages in the IDE. The process to do that is documented on the learning page of each board on the Adafruit website (see the "Resources" section).

To do this, you need to add the following URLs, seperated by commas in the "Additional boards manager URLs" setting in "File > Preferences" in the Arduino IDE:

Then use the following boards:

Feather Huzzah: "esp8266 > Adafruit Feather HUZZAH ESP8266"
Feather M0: "Adafruit SAMD Boards > Adafruit Feather M0 (SAMD21)"

Principle of operations

Despite the differences of implementation between the boards, the main progams follow this logic:

Initialize Wifi and check the connection status; if not connected, enter sleep mode and retry later.
Initialize the sensors using the initXXX() from Statox_Sensors, if needed (for sensors using I2C for example)
Read from the sensors using the readXXX() from Statox_Sensors. These functions should return their result as an array of float
Read the battery level. The M0 has a built-in voltage divider which can be read directly from a pin. For the Huzzah, I implement the tension divider myself and tied it to a pin.
Pass the read values to a function reponsible for creating a JSON document and posting it to the api.
Go to deep sleep mode and repeat.

Currently, the pins used by each sensors are directly in the Statox_Sensors library code, and the reading of each sensor is modified in the main loop depending on which physical sensors I attach to the board. My goal is to change this and have a proper configuration system in a header file to centralize the customization of each system in a single file.

Boards specificities

Feather Huzzah

The board does not support SSL well due to the lack of dedicated for encryption
Deep sleep is provided directly by the ESP class from the board installation. It makes both the board and the WiFi chip sleep properly. (Warning The function takes microseconds as argument)
A voltage divider is required to read the battery level, utilizing the only analog input pin of the board.
The Wifi and HTTP client libraries are coming directly from the board setup but could likely be replaced with WiFi101. (TODO)

Feather M0 Wifi

The WiFi chip's firmware needs to be updated to match the firmware expected by the WiFi101 library (documentation available on Adafruit's learning center)
- CAUTION Ensure you use WiFi101's setPins() function properly (done in initWiFi() in my code).
The board is supposed to support SSL but might need its certificate updated. This is also documented on Adafruit. I haven't tested yet and still use plain HTTP calls (booo)
The deep sleep feature is provided by the ArduinoLowPower library to put the ATSAMD21 chip to sleep, combined with a call to WiFi.end() from WiFi101 to stop the ATWINC1500 chip.

Resources

Libraries

ArduinoJson Used in api code for GET and POST requests
DHT sensor library (Its dependency "Adafruit Unified Sensor" is automatically installed by Arduino IDE when installing the lib) Used to read from the DHT11 sensor
BME280 Library 3.0.0 by Tyler Glenn Used to read from the BME280 sensor. I tried used the Adafruit library for the BME280 but it doesn't work with the sensor I bought from Velleman (whadda.com). I don't know if there is compability issue between the breakout boards and libraries.

Components

Main board: ESP8266 Adafruit Feather Huzzah

The ESP8266 supports a deep sleep mode which allows for very low current consumption while it is not active, it can read the DHT22 on a digital pin and the BME280 via I2C. The main drawback is that the board doesn't support SSL and HTTPS properly. In the future I'll probably want to switch to an ESP32.

Sensor: DHT22 Whadda Temperature and humidity sensor

Humidity: 0-100% (accuracy 2-5%) Temperature: -40 to 80°C (accuracy 0.5°C) Power: 3-5V Current: 2.5mA max current use during conversion (while requesting data) Sampling: No more than 0.5 Hz sampling rate (once every 2 seconds)

Sensor: BME280 Whadda Temperature, humidity and pressure sensor

Humidity: 0-100% (accuracy 3%) Temperature: -40 to 85°C (accuracy 1°C) Pressure: Not sure about range (accuracy 1hPa) Power: 1.71-3.6V Current: 3.6 uA @ 1Hz for humidity, temperature and pressure reading Sampling: 1 Hz sampling rate (once every seconds)

Bosch datasheet

statox / homeTrackerSensor