Wearing Your Monitor

Slip your arm through the straps with the band facing out. The sensor should be located underneath your armpit when you place your arm at your side.

Use the loop strap to loosen or tighten the band. Adjust the armband until it no longer slides around your arm. Make sure it is not too tight, you do not want to cut off circulation. 

Bluefruit LE Connect Usage

The Adafruit Bluefruit LE Connect app provides iOS & Android devices with a variety of tools to communicate with Bluefruit LE devices such as the Feather NRF52840. We'll be using Bluefruit LE Connect App to send temperature data using the MQTT protocol to Adafruit IO.

Once installed, open the Bluefruit LE Connect app. The app will automatically begin to scan for nearby Bluetooth LE devices.

Tap the Connect button next to the the Bluefruit52 device discovered by the app.

Once connected, the Bluefruit connect app will list its available modes. Tap the UART mode.

Next, you'll need to configure the Bluefruit LE Connect App's MQTT client with your Adafruit IO account information. 

Once configured, tap Connect

The MQTT Status will change to Connected, indicating that you've successfully connected to the Adafruit IO MQTT server.

Code Usage

Temperature Sensor Calibration

After connecting to the Bluefruit Connect App, the the armband will take twelve minutes to fully calibrate. 

Make sure the sensor is in your armpit and that your arm is firmly pressed against your side. After twelve minutes have passed, temperature readings will display on the UART monitor.

Viewing Sensor Data on Adafruit IO

Navigate to the Adafruit IO dashboard you created earlier. After 12 minutes have passed, the gauge and line block will update with the current temperature reading every minute. The line graph block updates and display the previous four hours of temperature data.

Fever Notifications

The reactive trigger you set up earlier will email you if the temperature increases beyond a temperature threshold.

If the temperature increases above the threshold you set, the Gauge block will change from a cool blue to bright yellow.

Configure the Fever Temperature Threshold

The Feather NRF52840's built-in NeoPixel will glow bright red if the temperature is above a configurable fever threshold. To change this value in the code, change the following line from:

// Maximum temperature value for armband's fever indicator

// NOTE: This is in degrees Fahrenheit

float fever_temp = 100.4;


// Maximum temperature value for armband's fever indicator

// NOTE: This is in degrees Fahrenheit


Change the Sensor Read Delay

By default, the code sends data to Adafruit IO every minute, then puts the temperature sensor and the NRF52840 to sleep.

If you want to change this code to read data at faster or slower intervals, change the following line from:

// Sensor read delay, in minutes

int sensor_delay = 1;


// Sensor read delay, in minutes

int sensor_delay = DESIRED_SENSOR_DELAY;

Keep in mind that every time the loop is executed, the microcontroller wakes up, executes code, and wirelessly sends data. You may want to increase the delay to conserve power. 

This guide was first published on Apr 07, 2020. It was last updated on Mar 25, 2020.

This page (Usage) was last updated on Mar 25, 2020.

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