Temperature and Humidity Monitor

Monitor temperature and humidity and send alerts using a Notecard and a BME280 sensor.

You Will Need

Hardware

• AC to USB adapter (power brick)
• USB A to micro USB cable
• LiPo battery with JST cable
• Notecarrier-F
• Notecard
• Swan MCU
• SparkFun Atmospheric Sensor Breakout - BME280 (Qwiic)
• Qwiic Cable

Software

• Visual Studio Code
• PlatformIO

Notehub Setup

Sign up for a free account on notehub.io and create a new project.

Hardware Setup

1. Assemble Notecard and Notecarrier as described here.
2. Plug the Swan into the Notecarrier, aligning the Swan's male headers with the Notecarrier's female headers.
3. (OPTIONAL) The BME280 breakout has an LED to indicate that its powered on. This draws a significant amount of current, especially compared to the sensor itself. To maximize battery life, you can disconnect this LED by cutting the JP1 jumper trace (see the schematic) on the back of the board with a hobby knife.
4. Plug one end of the Qwiic cable into one of the Notecarrier Qwiic ports and the other end into one of the Qwiic ports on the BME280 breakout board.
5. Plug the LiPo battery's JST cable into the Notecarrier port labeled "LIPO".
6. Connect the micro USB cable from your development PC to the Swan.

Notecard Firmware Setup

The Notecard should use firmware version 3.5.1 or higher. The simplest way to update firmware is to do an over-the-air update.

Swan Firmware Setup

This project has firmware implemented with both Arduino and Zephyr. To get your firmware up and running on the Swan, you can follow the documentation for either implementation:

• Arduino
• Zephyr

Operation

At this point, the Swan firmware should be running and you should start to see events show up on Notehub under your project's "Events" view. There are 3 important Notefiles.

data.qo

By default, the Swan will publish temperature and humidity data from the BME280 to this file every 3 minutes.

For example:

{
    "humidity": 30.705078125,
    "temperature": 24.340000152587891
}

You can change this interval by setting the environment variable report_interval. The unit for report_interval is seconds. The firmware reads from the BME280 every minute, so it's not particularly useful to set report_interval lower than 60 seconds. Note: If you modify any environment variables, wait at least 30 seconds for the changes to propagate to the Swan.

alarm.qo

By default, the firmware will send an alarm if the temperature falls outside the range [5, 33]C or the humidity falls outside the range [20, 70]% (relative humidity).

For example:

{
    "humidity":
    {
        "status": "high",
        "value": 31.19921875
    },
    "temperature":
    {
        "status": "ok",
        "value": 23.20999908447266
    }
}

The status field indicates the reason for the alarm. low means the value is below the minimum, high means the value is above the maximum, and ok means the value is in range. You should only ever see an alarm.qo note if at least one of the values is not ok.

You can use these environment variables to change the range:

• temperature_threshold_min: Lower bound of temperature range.
• temperature_threshold_max: Upper bound of temperature range.
• humidity_threshold_min: Lower bound of humidity range.
• humidity_threshold_max: Upper bound of humidity range.

_health.qo

Notes in this file indicate when USB power is lost or restored. When USB power is lost, you should see a note like this:

{
    "text": "USB power OFF {usb-disabled}"
}

And when USB power is restored, you should see:

{
    "text": "USB power ON {usb-enabled}"
}

Simulating a Power Outage

The LiPo battery acts as backup power in the event that USB power is lost. Once the battery is charged, you can test this functionality by doing the following:

1. Insert the power brick into a suitable electrical outlet and provide power to the Notecarrier via the micro USB cable.
2. Remove the power brick from the electrical outlet to simulate a power outage. The Notecard is now being powered by the battery.
3. After a short time, you will see a "USB power OFF" note in _health.qo on Notehub as mentioned in the previous section.
4. Reinsert the power brick into a suitable electrical outlet to simulate power being restored.
5. After a short time, you will see a "USB power ON" note in _health.qo on Notehub as mentioned in the previous section.