This guide assumes you've set up the Adafruit Bluefruit nRF52 Board Support Package.

Before proceeding with the code in this guide, you should be able to run the blinky sketch from the Arduino IDE. 

Make sure your board is selected:

  • Go to the Tools menu
  • Select Tools > Board > Adafruit Bluefruit nRF52840 Feather Express 

Copy the code below to the Arduino IDE. Click verify. Then, click Upload.

/*********************************************************************
 Learn Guide: BLE Temperature Monitoring Armband

 Adafruit invests time and resources providing this open source code,
 please support Adafruit and open-source hardware by purchasing
 products from Adafruit!

 MIT license, check LICENSE for more information
 All text above, and the splash screen below must be included in
 any redistribution
*********************************************************************/
#include <bluefruit.h>
#include <Adafruit_LittleFS.h>
#include <InternalFileSystem.h>
#include <Wire.h>
#include <Adafruit_NeoPixel.h>
#include "Adafruit_MCP9808.h"

// Read temperature in degrees Fahrenheit
#define TEMPERATURE_F
// uncomment the following line if you want to read temperature in degrees Celsius
//#define TEMPERATURE_C

// Feather NRF52840 Built-in NeoPixel
#define PIN 16
Adafruit_NeoPixel pixels(1, PIN, NEO_GRB + NEO_KHZ800);

// Maximum temperature value for armband's fever indicator
// NOTE: This is in degrees Fahrenheit
float fever_temp = 100.4;

// temperature calibration offset is +0.5 to +1.0 degree
// to make axillary temperature comparible to ear or temporal.
float temp_offset = 0.5;

// Sensor read delay, in minutes
int sensor_delay = 1;

// Measuring your armpit temperature for a minimum of 12 minutes
// is equivalent to measuring your core body temperature.
int calibration_time = 12;

// BLE transmit buffer
char temperature_buf [8];

// BLE Service
BLEDfu  bledfu;  // OTA DFU service
BLEDis  bledis;  // device information
BLEUart bleuart; // uart over ble
BLEBas  blebas;  // battery

// Create the MCP9808 temperature sensor object
Adafruit_MCP9808 tempsensor = Adafruit_MCP9808();

void setup() {
  Serial.begin(115200);
  Serial.println("Wearable BlueFruit Temperature Sensor");
  Serial.println("-------------------------------------\n");


  if (!tempsensor.begin(0x18)) {
    Serial.println("Couldn't find MCP9808! Check your connections and verify the address is correct.");
    while (1);
  }
  Serial.println("Found MCP9808!");

  // Sets the resolution of reading
  tempsensor.setResolution(3);

  // Configure BLE
  // Setup the BLE LED to be enabled on CONNECT
  // Note: This is actually the default behaviour, but provided
  // here in case you want to control this LED manually via PIN 19
  Bluefruit.autoConnLed(true);

  // Config the peripheral connection with maximum bandwidth 
  Bluefruit.configPrphBandwidth(BANDWIDTH_MAX);

  Bluefruit.begin();
  Bluefruit.setTxPower(4);    // Check bluefruit.h for supported values
  Bluefruit.setName("Bluefruit52");
  Bluefruit.Periph.setConnectCallback(connect_callback);
  Bluefruit.Periph.setDisconnectCallback(disconnect_callback);

  // To be consistent OTA DFU should be added first if it exists
  bledfu.begin();

  // Configure and Start Device Information Service
  bledis.setManufacturer("Adafruit Industries");
  bledis.setModel("Bluefruit Feather52");
  bledis.begin();

  // Configure and Start BLE Uart Service
  bleuart.begin();

  // Start BLE Battery Service
  blebas.begin();
  blebas.write(100);

  // Set up and start advertising
  startAdv();

  Serial.println("Please use Adafruit's Bluefruit LE app to connect in UART mode");

  // initialize neopixel object
  pixels.begin();

  // set all pixel colors to 'off'
  pixels.clear();
}

void loop() {

  // wakes up MCP9808 - power consumption ~200 mikro Ampere
  Serial.println("Wake up MCP9808");
  tempsensor.wake();

  // read and print the temperature
  Serial.print("Temp: "); 
  #if defined(TEMPERATURE_F)
    float temp = tempsensor.readTempF();
    // add temperature offset
    temp += temp_offset;
    Serial.print(temp);
    Serial.println("*F.");
  #elif defined(TEMPERATURE_C)
    float temp = tempsensor.readTempC();
    // add temperature offset
    temp += temp_offset;
    Serial.print(temp);
    Serial.println("*C.");
  #else
    #warning "Must define TEMPERATURE_C or TEMPERATURE_F!"
  #endif

  // set NeoPixels to RED if fever_temp
  if (temp >= fever_temp) {
    pixels.setPixelColor(1, pixels.Color(255, 0, 0));
    pixels.show();
  }

  // float to buffer
  snprintf(temperature_buf, sizeof(temperature_buf) - 1, "%0.*f", 1, temp);

  if (calibration_time == 0) {
      Serial.println("Writing to UART");
      // write to UART
      bleuart.write(temperature_buf);
  }
  else {
    Serial.print("Calibration time:");
    Serial.println(calibration_time);
    calibration_time-=1;
  }

  // shutdown MSP9808 - power consumption ~0.1 mikro Ampere
  Serial.println("Shutting down MCP9808");
  tempsensor.shutdown_wake(1);

  // sleep for sensor_delay minutes
  // NOTE: NRF delay() puts mcu into a low-power sleep mode
  delay(1000*60*sensor_delay);
}

void startAdv(void)
{
  // Advertising packet
  Bluefruit.Advertising.addFlags(BLE_GAP_ADV_FLAGS_LE_ONLY_GENERAL_DISC_MODE);
  Bluefruit.Advertising.addTxPower();

  // Include bleuart 128-bit uuid
  Bluefruit.Advertising.addService(bleuart);

  // Secondary Scan Response packet (optional)
  // Since there is no room for 'Name' in Advertising packet
  Bluefruit.ScanResponse.addName();
  
  /* Start Advertising
   * - Enable auto advertising if disconnected
   * - Interval:  fast mode = 20 ms, slow mode = 152.5 ms
   * - Timeout for fast mode is 30 seconds
   * - Start(timeout) with timeout = 0 will advertise forever (until connected)
   * 
   * For recommended advertising interval
   * https://developer.apple.com/library/content/qa/qa1931/_index.html   
   */
  Bluefruit.Advertising.restartOnDisconnect(true);
  Bluefruit.Advertising.setInterval(32, 244);    // in unit of 0.625 ms
  Bluefruit.Advertising.setFastTimeout(30);      // number of seconds in fast mode
  Bluefruit.Advertising.start(0);                // 0 = Don't stop advertising after n seconds  
}

// callback invoked when central connects
void connect_callback(uint16_t conn_handle)
{
  // Get the reference to current connection
  BLEConnection* connection = Bluefruit.Connection(conn_handle);

  char central_name[32] = { 0 };
  connection->getPeerName(central_name, sizeof(central_name));

  Serial.print("Connected to ");
  Serial.println(central_name);
}

/**
 * Callback invoked when a connection is dropped
 * @param conn_handle connection where this event happens
 * @param reason is a BLE_HCI_STATUS_CODE which can be found in ble_hci.h
 */
void disconnect_callback(uint16_t conn_handle, uint8_t reason)
{
  (void) conn_handle;
  (void) reason;

  Serial.println();
  Serial.print("Disconnected, reason = 0x"); Serial.println(reason, HEX);
}

After you've successfully uploaded the code to your Feather, toggle the switch to turn the power on. The blue LED labeled CONN should blink. 

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

This page (Arduino Code) was last updated on Apr 20, 2021.

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