This code is tested with an Android 9, the extension BLE 20201223 and an ESP32.
If it doesn't work for you with that extension, try this ... Bluetooth bLE not connect
/*
Based on Neil Kolban example for IDF:
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/tests/BLE%20Tests/SampleWrite.cpp
Ported to Arduino ESP32 by Evandro Copercini
*/
// Modificado por Juan Antonio Villalpando.
// http://kio4.com/arduino/160i_Wemos_ESP32_BLE.htm
#include <BLEDevice.h>
#include <BLEUtils.h>
#include <BLEServer.h>
String valor;
#define SERVICE_UUID "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"
class MyCallbacks: public BLECharacteristicCallbacks {
void onWrite(BLECharacteristic *pCharacteristic) {
std::string value = pCharacteristic->getValue();
if (value.length() > 0) {
valor = "";
for (int i = 0; i < value.length(); i++){
// Serial.print(value[i]); // Presenta value.
valor = valor + value[i];
}
Serial.println("*********");
Serial.print("valor = ");
Serial.println(valor); // Presenta valor.
}
}
};
void setup() {
Serial.begin(115200);
BLEDevice::init("MyESP32");
BLEServer *pServer = BLEDevice::createServer();
BLEService *pService = pServer->createService(SERVICE_UUID);
BLECharacteristic *pCharacteristic = pService->createCharacteristic(
CHARACTERISTIC_UUID,
BLECharacteristic::PROPERTY_READ |
BLECharacteristic::PROPERTY_WRITE
);
pCharacteristic->setCallbacks(new MyCallbacks());
pCharacteristic->setValue("Hello World");
pService->start();
BLEAdvertising *pAdvertising = pServer->getAdvertising();
pAdvertising->start();
}
void loop() {
// put your main code here, to run repeatedly:
delay(2000);
// Serial.println("valor en el loop = ");
// Serial.println(valor); // Presenta valor.
}
The default Minimum Transmission Unit MTU is 20 bytes.
With block RequestMTU, I have been able to increase it to 22 bytes.
/*
Based on Neil Kolban example for IDF:
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/tests/BLE%20Tests/SampleWrite.cpp
Ported to Arduino ESP32 by Evandro Copercini
*/
// Modificado por Juan Antonio Villalpando.
// http://kio4.com/arduino/160i_Wemos_ESP32_BLE.htm
#include <BLEDevice.h>
#include <BLEUtils.h>
#include <BLEServer.h>
String valor;
int aleatorio;
String alea = "2";
#define SERVICE_UUID "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"
class MyCallbacks: public BLECharacteristicCallbacks {
void onWrite(BLECharacteristic *pCharacteristic) {
std::string value = pCharacteristic->getValue();
pCharacteristic->setValue(alea.c_str()); // Pone el numero aleatorio
if (value.length() > 0) {
valor = "";
for (int i = 0; i < value.length(); i++){
// Serial.print(value[i]); // Presenta value.
valor = valor + value[i];
}
Serial.println("*********");
Serial.print("valor = ");
Serial.println(valor); // Presenta valor.
}
}
};
void setup() {
Serial.begin(115200);
BLEDevice::init("MyESP32");
BLEServer *pServer = BLEDevice::createServer();
BLEService *pService = pServer->createService(SERVICE_UUID);
BLECharacteristic *pCharacteristic = pService->createCharacteristic(
CHARACTERISTIC_UUID,
BLECharacteristic::PROPERTY_READ |
BLECharacteristic::PROPERTY_WRITE
);
pCharacteristic->setCallbacks(new MyCallbacks());
pCharacteristic->setValue("Iniciado.");
pService->start();
BLEAdvertising *pAdvertising = pServer->getAdvertising();
pAdvertising->start();
}
void loop() {
// put your main code here, to run repeatedly:
delay(2000);
//Serial.println("valor en el loop = ");
//Serial.println(valor); // Presenta valor.
aleatorio = random(1,100); // Crea el numero aleatorio.
alea = (String) aleatorio; // Lo convierte en String.
}
6.- ESP32 sends automatically (Notify) a random number to App. p110i_esp32_ble_notifica.aia (220.6 KB) The Bluetooth LE specification includes a mechanism known as notify that lets you know when data’s changed. When notify on a characteristic is enabled and the sender writes to it, the new value is automatically sent to the receiver, without the receiver explicitly issuing a read command. (Reference ArduinoBLE)
ESP32 code generates a random number every 500 milisecond and notifies (sends) it to the application.
/*
Based on Neil Kolban example for IDF:
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/tests/BLE%20Tests/SampleNotify.cpp
Ported to Arduino ESP32 by Evandro Copercini updated by chegewara
Create a BLE server that, once we receive a connection, will send periodic notifications.
A connect hander associated with the server starts a background task that performs notification
every couple of seconds.
*/
// Modificado por Juan A. Villalpando
// http://kio4.com/arduino/160i_Wemos_ESP32_BLE.htm
#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>
BLEServer* pServer = NULL;
BLECharacteristic* pCharacteristic = NULL;
bool deviceConnected = false;
bool oldDeviceConnected = false;
uint32_t value = 0;
// See the following for generating UUIDs:
// https://www.uuidgenerator.net/
#define SERVICE_UUID "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"
class MyServerCallbacks: public BLEServerCallbacks {
void onConnect(BLEServer* pServer) {
deviceConnected = true;
};
void onDisconnect(BLEServer* pServer) {
deviceConnected = false;
}
};
void setup() {
Serial.begin(115200);
// Create the BLE Device
BLEDevice::init("MyESP32");
// Create the BLE Server
pServer = BLEDevice::createServer();
pServer->setCallbacks(new MyServerCallbacks());
// Create the BLE Service
BLEService *pService = pServer->createService(SERVICE_UUID);
// Create a BLE Characteristic
pCharacteristic = pService->createCharacteristic(
CHARACTERISTIC_UUID,
BLECharacteristic::PROPERTY_READ |
BLECharacteristic::PROPERTY_WRITE |
BLECharacteristic::PROPERTY_NOTIFY |
BLECharacteristic::PROPERTY_INDICATE
);
// https://www.bluetooth.com/specifications/gatt/viewer?
// attributeXmlFile=org.bluetooth.descriptor.gatt.client_characteristic_configuration.xml
// Create a BLE Descriptor
pCharacteristic->addDescriptor(new BLE2902());
// Start the service
pService->start();
// Start advertising
BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
pAdvertising->addServiceUUID(SERVICE_UUID);
pAdvertising->setScanResponse(false);
pAdvertising->setMinPreferred(0x0); // set value to 0x00 to not advertise this parameter
BLEDevice::startAdvertising();
Serial.println("Waiting a client connection to notify...");
}
void loop() {
// notify changed value
if (deviceConnected) {
// pCharacteristic->setValue((uint8_t*)&value, 4);
int aleatorio = random(1,100); // Crea el numero aleatorio.
String alea = (String) aleatorio; // Lo convierte en String.
pCharacteristic->setValue(alea.c_str()); // Pone el numero aleatorio
pCharacteristic->notify();
delay(500); // bluetooth stack will go into congestion, if too many packets are sent.
}
// disconnecting
if (!deviceConnected && oldDeviceConnected) {
delay(500); // give the bluetooth stack the chance to get things ready
pServer->startAdvertising(); // restart advertising
Serial.println("start advertising");
oldDeviceConnected = deviceConnected;
}
// connecting
if (deviceConnected && !oldDeviceConnected) {
// do stuff here on connecting
oldDeviceConnected = deviceConnected;
}
}
/*
Video: https://www.youtube.com/watch?v=oCMOYS71NIU
Based on Neil Kolban example for IDF:
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/tests/BLE%20Tests/SampleNotify.cpp
Ported to Arduino ESP32 by Evandro Copercini
updated by chegewara
Create a BLE server that, once we receive a connection, will send periodic notifications.
A connect hander associated with the server starts a background task that performs notification
every couple of seconds.
*/
// Modificado por Juan A. Villalpando
// http://kio4.com/arduino/160i_Wemos_ESP32_BLE.htm
#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>
String valor;
BLEServer* pServer = NULL;
BLECharacteristic* pCharacteristic = NULL;
bool deviceConnected = false;
bool oldDeviceConnected = false;
//uint32_t value = 0;
#define SERVICE_UUID "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"
class MyServerCallbacks: public BLEServerCallbacks {
void onConnect(BLEServer* pServer) {
deviceConnected = true;
};
void onDisconnect(BLEServer* pServer) {
deviceConnected = false;
}
};
////////////////////// WriteStrings /////////////////////////////
class MyCallbacks: public BLECharacteristicCallbacks {
void onWrite(BLECharacteristic *pCharacteristic) {
std::string value = pCharacteristic->getValue();
if (value.length() > 0) {
valor = "";
for (int i = 0; i < value.length(); i++){
// Serial.print(value[i]); // Presenta value.
valor = valor + value[i];
}
Serial.println("*********");
Serial.print("valor = ");
Serial.println(valor); // Presenta valor.
}
}
};
///////////////////////////////////////////////////
void setup() {
Serial.begin(115200);
// Create the BLE Device
BLEDevice::init("MyESP32");
// Create the BLE Server
pServer = BLEDevice::createServer();
pServer->setCallbacks(new MyServerCallbacks());
// Create the BLE Service
BLEService *pService = pServer->createService(SERVICE_UUID);
// Create a BLE Characteristic
pCharacteristic = pService->createCharacteristic(
CHARACTERISTIC_UUID,
BLECharacteristic::PROPERTY_READ |
BLECharacteristic::PROPERTY_WRITE |
BLECharacteristic::PROPERTY_NOTIFY |
BLECharacteristic::PROPERTY_INDICATE
);
// https://www.bluetooth.com/specifications/gatt/viewer?
// attributeXmlFile=org.bluetooth.descriptor.gatt.client_characteristic_configuration.xml
// Create a BLE Descriptor
pCharacteristic->addDescriptor(new BLE2902());
// Esta línea es para el WriteStrings:
pCharacteristic->setCallbacks(new MyCallbacks());
// Start the service
pService->start();
// Start advertising
BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
pAdvertising->addServiceUUID(SERVICE_UUID);
pAdvertising->setScanResponse(false);
pAdvertising->setMinPreferred(0x0); // set value to 0x00 to not advertise this parameter
BLEDevice::startAdvertising();
Serial.println("Waiting a client connection to notify...");
}
void loop() {
// notify changed value
if (deviceConnected) {
std::string value = pCharacteristic->getValue();
// pCharacteristic->setValue((uint8_t*)&value, 4);
int doble = valor.toInt() * 2 ;
String doblado = (String) doble; // Lo convierte en String.
pCharacteristic->setValue(doblado.c_str()); // Pone el numero doble
pCharacteristic->notify();
delay(5); // bluetooth stack will go into congestion, if too many packets are sent.
}
// disconnecting
if (!deviceConnected && oldDeviceConnected) {
delay(500); // give the bluetooth stack the chance to get things ready
pServer->startAdvertising(); // restart advertising
Serial.println("start advertising");
oldDeviceConnected = deviceConnected;
}
// connecting
if (deviceConnected && !oldDeviceConnected) {
// do stuff here on connecting
oldDeviceConnected = deviceConnected;
}
}
Juan,
This is great work! I am looking for a way to modify this so that instead of printing the result to the serial monitor it prints it to a 16x2 I2C LCD screen. I am able to get this working in part by adding lcd.print(valor); to the main loop, but of course then it just loops that text on the screen. What I would like to be able to do is to send a bit of text, have it stay on the screen until another string of text is sent. Could you point me in the right direction?
Sorry for the bother…
Is this a simple example for receive a command from Esp32 (or Arduino)?
I tried one.
I mean: We can turn on/off a led on Esp32 (Arduino) from cell phone.
But I am not able to turn on/off a “led” on cell phone from Esp32 (Arduino)…
I tried… But it works only if you repress on/off from cell phone…
So I am trying to make a simple app with a simple “ON” or “OFF” and in Esp32 (Arduino) building simple button… (simply writing on terminal)…
How do it???
“When BluetoothLE1.StringsReceived” doesn’t work…
/* Based on Neil Kolban example for IDF:
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/tests/BLE%20Tests/SampleNotify.cpp
Ported to Arduino ESP32 by Evandro Copercini updated by chegewara
Create a BLE server that, once we receive a connection, will send periodic notifications.
A connect hander associated with the server starts a background task that performs notification
every couple of seconds. */
// Modificado por Juan A. Villalpando
// http://kio4.com/arduino/160i_Wemos_ESP32_BLE.htm
#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>
#define pin12 12 // pin12 PushButton
#define pin2 2 // pin2 LED2
int valor12; // Status PushButton
String output ="LOW"; // Output to App. Notify.
BLEServer* pServer = NULL;
BLECharacteristic* pCharacteristic = NULL;
bool deviceConnected = false;
bool oldDeviceConnected = false;
uint32_t value = 0;
#define SERVICE_UUID "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"
class MyServerCallbacks: public BLEServerCallbacks {
void onConnect(BLEServer* pServer) {
deviceConnected = true;
};
void onDisconnect(BLEServer* pServer) {
deviceConnected = false;
}
};
void setup() {
pinMode(pin12, INPUT); // pin12 PushButton
pinMode(pin2, OUTPUT); // pin2 LED2
Serial.begin(115200);
// Create the BLE Device
BLEDevice::init("MyESP32");
// Create the BLE Server
pServer = BLEDevice::createServer();
pServer->setCallbacks(new MyServerCallbacks());
// Create the BLE Service
BLEService *pService = pServer->createService(SERVICE_UUID);
// Create a BLE Characteristic
pCharacteristic = pService->createCharacteristic(
CHARACTERISTIC_UUID,
BLECharacteristic::PROPERTY_READ |
BLECharacteristic::PROPERTY_WRITE |
BLECharacteristic::PROPERTY_NOTIFY |
BLECharacteristic::PROPERTY_INDICATE
);
// Create a BLE Descriptor
pCharacteristic->addDescriptor(new BLE2902());
// Start the service
pService->start();
// Start advertising
BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
pAdvertising->addServiceUUID(SERVICE_UUID);
pAdvertising->setScanResponse(false);
pAdvertising->setMinPreferred(0x0); // set value to 0x00 to not advertise this parameter
BLEDevice::startAdvertising();
Serial.println("Waiting a client connection to notify...");
}
void loop() {
// notify changed value
if (deviceConnected) {
pCharacteristic->setValue(output.c_str()); // Output
pCharacteristic->notify();
valor12 = digitalRead(pin12); // Read pin12 --> valor12. ( 0 or 1)
if (valor12 == HIGH) {
digitalWrite(pin2, HIGH); // if valor12 is HIGH, set pin2 HIGH
Serial.println("Pulsado");
output ="HIGH"; // Notify HIGH
}
if (valor12 == LOW) {
digitalWrite(pin2, LOW); // If valor12 is LOW, set pin2 LOW
Serial.println("No Pulsado");
output ="LOW"; // Notify LOW
}
delay(100); // bluetooth stack will go into congestion, if too many packets are sent.
}
// disconnecting
if (!deviceConnected && oldDeviceConnected) {
delay(500); // give the bluetooth stack the chance to get things ready
pServer->startAdvertising(); // restart advertising
Serial.println("start advertising");
oldDeviceConnected = deviceConnected;
}
// connecting
if (deviceConnected && !oldDeviceConnected) {
// do stuff here on connecting
oldDeviceConnected = deviceConnected;
}
}
@Juan_Antonio, I’m getting started with esp32 BLE connection and MIT app inventor. I don’t know what is happening, but I got this error when I try to use any off the apps. Can someone help me?
Note: I’m just copying and pasting both code and app