Would like to ask for assistance with the code below. It's the Adafruit Bluefruit Atmega32U LE module with Adafruit's Arduino IDE example "heart-rate monitor" sketch. The code uses the hardware SPI setup with Adafruit's BLE code between the Atmega32U and the nRF51822 using AT Commands built into a BLE stack by Adafruit.

It works at the same speed in real-time on the PC's Arduino IDE USB serial terminal and also on the Android phone's nRF Connect app or any other BLE app that can read "notifications".

Problem: If remove the module from the PC's USB (thus the serial stopped and only using BLE) the update rate on the BLE Android app slows down to 5 second intervals compared to the near real-time speed while connected to USB. I tried many things, including commenting out the Serial commands in the void loop() and also the delay(), but no change. As if the BLE stack by Adafruit would have a update period limitation. According to Adafruit, they do not give access to to their BLE stack. But I could possibly load another BLE stack on this nRF51822 chip. Also I do have the Adafruit Sniffer with Wireshark, but not an expert using it.

How can I get less than 1 second update rates? The data stream is not in 1 second intervals. Maybe 10-15 seconds between readings, but I need it updated within 1 second of being read from the sensor.


#include <Arduino.h>    
#include <SPI.h>     
#include "Adafruit_BLE.h"
#include "Adafruit_BluefruitLE_SPI.h"
#include "Adafruit_BluefruitLE_UART.h"

#include "BluefruitConfig.h"

  #include <SoftwareSerial.h>

// Create the bluefruit object, either software serial...uncomment these lines
SoftwareSerial bluefruitSS = SoftwareSerial(BLUEFRUIT_SWUART_TXD_PIN, BLUEFRUIT_SWUART_RXD_PIN);

Adafruit_BluefruitLE_UART ble(bluefruitSS, BLUEFRUIT_UART_MODE_PIN,

/* ...or hardware serial, which does not need the RTS/CTS pins. Uncomment this line */

/* ...hardware SPI, using SCK/MOSI/MISO hardware SPI pins and then user selected CS/IRQ/RST */

/* ...software SPI, using SCK/MOSI/MISO user-defined SPI pins and then user selected CS/IRQ/RST */
//                             BLUEFRUIT_SPI_MOSI, BLUEFRUIT_SPI_CS,
//                             BLUEFRUIT_SPI_IRQ, BLUEFRUIT_SPI_RST);

// A small helper
void error(const __FlashStringHelper*err) {
  while (1);

/* The service information */

int32_t hrmServiceId;
int32_t hrmMeasureCharId;
int32_t hrmLocationCharId;
    @brief  Sets up the HW an the BLE module (this function is called
            automatically on startup)
void setup(void)
  while (!Serial); // required for Flora & Micro

  boolean success;

  Serial.println(F("Adafruit Bluefruit Heart Rate Monitor (HRM) Example"));


  /* Initialise the module */
  Serial.print(F("Initialising the Bluefruit LE module: "));

  if ( !ble.begin(VERBOSE_MODE) )
    error(F("Couldn't find Bluefruit, make sure it's in CoMmanD mode & check wiring?"));
  Serial.println( F("OK!") );

  /* Perform a factory reset to make sure everything is in a known state */
  Serial.println(F("Performing a factory reset: "));
  if (! ble.factoryReset() ){
       error(F("Couldn't factory reset"));

  /* Disable command echo from Bluefruit */

  Serial.println("Requesting Bluefruit info:");
  /* Print Bluefruit information */

  // this line is particularly required for Flora, but is a good idea
  // anyways for the super long lines ahead!
  // ble.setInterCharWriteDelay(5); // 5 ms

  /* Change the device name to make it easier to find */
  Serial.println(F("Setting device name to 'Bluefruit HRM': "));

  if (! ble.sendCommandCheckOK(F("AT+GAPDEVNAME=Bluefruit HRM")) ) {
    error(F("Could not set device name?"));

  /* Add the Heart Rate Service definition */
  /* Service ID should be 1 */
  Serial.println(F("Adding the Heart Rate Service definition (UUID = 0x180D): "));
  success = ble.sendCommandWithIntReply( F("AT+GATTADDSERVICE=UUID=0x180D"), &hrmServiceId);
  if (! success) {
    error(F("Could not add HRM service"));

  /* Add the Heart Rate Measurement characteristic */
  /* Chars ID for Measurement should be 1 */
  Serial.println(F("Adding the Heart Rate Measurement characteristic (UUID = 0x2A37): "));
  success = ble.sendCommandWithIntReply( F("AT+GATTADDCHAR=UUID=0x2A37, PROPERTIES=0x10, MIN_LEN=2, MAX_LEN=3, VALUE=00-40"), &hrmMeasureCharId);
    if (! success) {
    error(F("Could not add HRM characteristic"));

  /* Add the Body Sensor Location characteristic */
  /* Chars ID for Body should be 2 */
  Serial.println(F("Adding the Body Sensor Location characteristic (UUID = 0x2A38): "));
  success = ble.sendCommandWithIntReply( F("AT+GATTADDCHAR=UUID=0x2A38, PROPERTIES=0x02, MIN_LEN=1, VALUE=3"), &hrmLocationCharId);
    if (! success) {
    error(F("Could not add BSL characteristic"));

  /* Add the Heart Rate Service to the advertising data (needed for Nordic apps to detect the service) */
  Serial.print(F("Adding Heart Rate Service UUID to the advertising payload: "));
  ble.sendCommandCheckOK( F("AT+GAPSETADVDATA=02-01-06-05-02-0d-18-0a-18") );

  /* Reset the device for the new service setting changes to take effect */
  Serial.print(F("Performing a SW reset (service changes require a reset): "));


/** Send randomized heart rate data continuously **/
void loop(void)
  int heart_rate = random(50, 100);

  //Serial.print(F("Updating HRM value to "));
 // Serial.println(F(" BPM"));

  /* Command is sent when \n (\r) or println is called */
  /* AT+GATTCHAR=CharacteristicID,value */
  ble.print( F("AT+GATTCHAR=") );
  ble.print( hrmMeasureCharId );
  ble.print( F(",00-") );
  ble.println(heart_rate, HEX);

  /* Check if command executed OK */
 // if ( !ble.waitForOK() )
 // {
   // Serial.println(F("Failed to get response!"));

  /* Delay before next measurement update */
 // delay(1000);

/////////////////AND BELOW IS THE BluefruitConfig.h TAB in ARDUINO IDE --This is a separate file under a new tab in the IDE////////////////..

// ----------------------------------------------------------------------------------------------
// These settings are used in both SW UART, HW UART and SPI mode
// ----------------------------------------------------------------------------------------------
#define BUFSIZE                        128   // Size of the read buffer for incoming data
#define VERBOSE_MODE                   true  // If set to 'true' enables debug output

// ----------------------------------------------------------------------------------------------
// The following macros declare the pins that will be used for 'SW' serial.
// You should use this option if you are connecting the UART Friend to an UNO
// ----------------------------------------------------------------------------------------------
#define BLUEFRUIT_SWUART_RXD_PIN       9    // Required for software serial!
#define BLUEFRUIT_SWUART_TXD_PIN       10   // Required for software serial!
#define BLUEFRUIT_UART_CTS_PIN         11   // Required for software serial!
#define BLUEFRUIT_UART_RTS_PIN         8    // Optional, set to -1 if unused

// ----------------------------------------------------------------------------------------------
// The following macros declare the HW serial port you are using. Uncomment
// this line if you are connecting the BLE to Leonardo/Micro or Flora
// ----------------------------------------------------------------------------------------------
#ifdef Serial1    // this makes it not complain on compilation if there's no Serial1
  #define BLUEFRUIT_HWSERIAL_NAME      Serial1

// ----------------------------------------------------------------------------------------------
// The following sets the optional Mode pin, its recommended but not required
// ----------------------------------------------------------------------------------------------
#define BLUEFRUIT_UART_MODE_PIN        12    // Set to -1 if unused

// ----------------------------------------------------------------------------------------------
// The following macros declare the pins to use for HW and SW SPI communication.
// SCK, MISO and MOSI should be connected to the HW SPI pins on the Uno when
// using HW SPI.  This should be used with nRF51822 based Bluefruit LE modules
// that use SPI (Bluefruit LE SPI Friend).
// ----------------------------------------------------------------------------------------------
#define BLUEFRUIT_SPI_CS               8
#define BLUEFRUIT_SPI_IRQ              7
#define BLUEFRUIT_SPI_RST              4    // Optional but recommended, set to -1 if unused

// ----------------------------------------------------------------------------------------------
// The following macros declare the pins to use for SW SPI communication.
// This should be used with nRF51822 based Bluefruit LE modules that use SPI
// (Bluefruit LE SPI Friend).
// ----------------------------------------------------------------------------------------------
#define BLUEFRUIT_SPI_SCK              13
#define BLUEFRUIT_SPI_MISO             12
#define BLUEFRUIT_SPI_MOSI             11
  • Thank you @Edgar Bonet for helping with the code format edit. Appreciate it. I was a bit late figuring it out.
    – TommyS
    May 24, 2020 at 9:43
  • 1
    first remove while (!Serial);
    – Juraj
    May 24, 2020 at 11:04
  • I removed the "while (!Serial)" and still has the 5 second lag on both Android and iOS apps receiving data. It's quite regular 5 seconds, not random intervals. Also, there is nothing left in the void loop() that can slow things down. If I open the serial terminal box in the Arduino IDE then the data streams at full-speed in real-time. I wonder, if there is some bug in the Adafruit BLE stack? No source code is given out. Wondering, if there is any way to add in the code to run the serial terminal (or something to that effect) without actually having the USB cable plugged in the PC?
    – TommyS
    May 26, 2020 at 16:16
  • How can I test the BLE for max speed? I ran an Adafruit BLE example program that tested the UART side of the BLE and had about 1-2 Kbs datastream, but this heartrate program uses GATT BLE and not UART.
    – TommyS
    May 26, 2020 at 16:25
  • try to remove Serial.begin or add Serial.end() at the end of setup()
    – Juraj
    May 26, 2020 at 16:26

1 Answer 1


The "verbose" error check mode for debug in the "BluefruitConfig.h" tab slowed down the flow of BLE data. I changed it from "true" to "false" to turn it off.

#define VERBOSE_MODE true  // If set to 'true' enables debug output

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