BLE serial gibberish

This BLE Client script compiles and uploads with no issue, but the serial output is garbage:

This is Termite:

This is the VSCode output:
�␙H�␔)Do��3�␓��!"S����R����!�b5�RS�`��␐9␂R��)���cr夌c���!␌) ␋B�~�␐9"��e␞B␔B

There are characters in this mess. I see numbers. I’m expecting numbers.

Check the baud rate in the code, then make sure that monitor_speed = baudrate in the platformio.ini file.

Failing that, try a baudrate that isn’t 115200 as that one is well out of error percentage range. (For an ATmega328 that is.)


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Baud rate isn’t in the .ini, and everything is set to 9600.

I think I’m seeing reported data AND gibberish.

Output is supposed to be text and UUIDs.

I might try to display something on OLED.

"control reaches end of non-void function at line 98, which is a }

 * A BLE client example that is rich in capabilities.
 * There is a lot new capabilities implemented.
 * author unknown
 * updated by chegewara
#include <Arduino.h>
#include "BLEDevice.h"
//#include "BLEScan.h"

// The remote service we wish to connect to.
static BLEUUID serviceUUID("4fafc201-1fb5-459e-8fcc-c5c9c331914b");
// The characteristic of the remote service we are interested in.
static BLEUUID charUUID("beb5483e-36e1-4688-b7f5-ea07361b26a8");

static boolean doConnect = false;
static boolean connected = false;
static boolean doScan = false;
static BLERemoteCharacteristic *pRemoteCharacteristic;
static BLEAdvertisedDevice *myDevice;

static void notifyCallback(
    BLERemoteCharacteristic *pBLERemoteCharacteristic,
    uint8_t *pData,
    size_t length,
    bool isNotify)
  Serial.print("Notify callback for characteristic ");
  Serial.print(" of data length ");
  Serial.print("data: ");
  Serial.println((char *)pData);

class MyClientCallback : public BLEClientCallbacks
  void onConnect(BLEClient *pclient)

  void onDisconnect(BLEClient *pclient)
    connected = false;

bool connectToServer()
  Serial.print("Forming a connection to ");

  BLEClient *pClient = BLEDevice::createClient();
  Serial.println(" - Created client");

  pClient->setClientCallbacks(new MyClientCallback());

  // Connect to the remove BLE Server.
  pClient->connect(myDevice); // if you pass BLEAdvertisedDevice instead of address, it will be recognized type of peer device address (public or private)
  Serial.println(" - Connected to server");

  // Obtain a reference to the service we are after in the remote BLE server.
  BLERemoteService *pRemoteService = pClient->getService(serviceUUID);
  if (pRemoteService == nullptr)
    Serial.print("Failed to find our service UUID: ");
    return false;
  Serial.println(" - Found our service");

  // Obtain a reference to the characteristic in the service of the remote BLE server.
  pRemoteCharacteristic = pRemoteService->getCharacteristic(charUUID);
  if (pRemoteCharacteristic == nullptr)
    Serial.print("Failed to find our characteristic UUID: ");
    return false;
  Serial.println(" - Found our characteristic");

  // Read the value of the characteristic.
  if (pRemoteCharacteristic->canRead())
    std::string value = pRemoteCharacteristic->readValue();
    Serial.print("The characteristic value was: ");

  if (pRemoteCharacteristic->canNotify())

  connected = true;
 * Scan for BLE servers and find the first one that advertises the service we are looking for.
class MyAdvertisedDeviceCallbacks : public BLEAdvertisedDeviceCallbacks
   * Called for each advertising BLE server.
  void onResult(BLEAdvertisedDevice advertisedDevice)
    Serial.print("BLE Advertised Device found: ");

    // We have found a device, let us now see if it contains the service we are looking for.
    if (advertisedDevice.haveServiceUUID() && advertisedDevice.isAdvertisingService(serviceUUID))

      myDevice = new BLEAdvertisedDevice(advertisedDevice);
      doConnect = true;
      doScan = true;

    } // Found our server
  }   // onResult
};    // MyAdvertisedDeviceCallbacks

void setup()
  Serial.println("Starting Arduino BLE Client application...");

  // Retrieve a Scanner and set the callback we want to use to be informed when we
  // have detected a new device.  Specify that we want active scanning and start the
  // scan to run for 5 seconds.
  BLEScan *pBLEScan = BLEDevice::getScan();
  pBLEScan->setAdvertisedDeviceCallbacks(new MyAdvertisedDeviceCallbacks());
  pBLEScan->start(5, false);
} // End of setup.

// This is the Arduino main loop function.
void loop()

  // If the flag "doConnect" is true then we have scanned for and found the desired
  // BLE Server with which we wish to connect.  Now we connect to it.  Once we are
  // connected we set the connected flag to be true.
  if (doConnect == true)
    if (connectToServer())
      Serial.println("We are now connected to the BLE Server.");
      Serial.println("We have failed to connect to the server; there is nothin more we will do.");
    doConnect = false;

  // If we are connected to a peer BLE Server, update the characteristic each time we are reached
  // with the current time since boot.
  if (connected)
    String newValue = "Time since boot: " + String(millis() / 1000);
    Serial.println("Setting new characteristic value to \"" + newValue + "\"");

    // Set the characteristic's value to be the array of bytes that is actually a string.
    pRemoteCharacteristic->writeValue(newValue.c_str(), newValue.length());
  else if (doScan)
    BLEDevice::getScan()->start(0); // this is just eample to start scan after disconnect, most likely there is better way to do it in arduino

  delay(1000); // Delay a second between loops.
} // End of loop

None of the characters that make it through appear to have any meaning.

is the end of a function which is declared as

returning bool. The function doesn’t in this code path though. Thus it’s technically undefined behavior and can crash the program. The compiler is correct with


return true;

should be placed at the end of the function to indicate success.

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No it isn’t! In this function:

It is indeed 9600. However, in this one, it is 115200:

Add monitor_speed = 115200 to the platformio.ini file, just to be sure that the code and monitor definitely match up.

This function returns false in a couple of places. However, if it reaches the end, it does not return a value. I assume it should return true?


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