How to send Bluetooth data from ESP32 in arduino? - arduino

Question

Easy to handle received data with BLE but can't send data.
I'm using ESP32 BLE Uart code.
It's easy to get data from RxCharateristic but I don't know how to send data.
I'm trying to use TxCharacteristic to send data with BLE.
#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>
BLEServer *pServer = NULL;
BLECharacteristic * pTxCharacteristic;
bool deviceConnected = false;
bool oldDeviceConnected = false;
uint8_t txValue = 0;
// See the following for generating UUIDs:
// https://www.uuidgenerator.net/
#define SERVICE_UUID "6E400001-B5A3-F393-E0A9-E50E24DCCA9E" // UART service UUID
#define CHARACTERISTIC_UUID_RX "6E400002-B5A3-F393-E0A9-E50E24DCCA9E"
#define CHARACTERISTIC_UUID_TX "6E400003-B5A3-F393-E0A9-E50E24DCCA9E"
class MyServerCallbacks: public BLEServerCallbacks {
void onConnect(BLEServer* pServer) {
deviceConnected = true;
};
void onDisconnect(BLEServer* pServer) {
deviceConnected = false;
}
};
class MyCallbacks: public BLECharacteristicCallbacks {
void onWrite(BLECharacteristic *pCharacteristic) {
std::string rxValue = pCharacteristic->getValue();
if (rxValue.length() > 0) {
Serial.println("*********");
Serial.print("Received Value: ");
for (int i = 0; i < rxValue.length(); i++){
Serial.print(rxValue[i]);
}
}
}
};
void setup() {
Serial.begin(115200);
// Create the BLE Device
BLEDevice::init("TheOneSystem");
// 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
pTxCharacteristic = pService->createCharacteristic(
CHARACTERISTIC_UUID_TX,
BLECharacteristic::PROPERTY_NOTIFY
);
pTxCharacteristic->addDescriptor(new BLE2902());
BLECharacteristic * pRxCharacteristic = pService->createCharacteristic(
CHARACTERISTIC_UUID_RX,
BLECharacteristic::PROPERTY_WRITE
);
pRxCharacteristic->setCallbacks(new MyCallbacks());
// Start the service
pService->start();
// Start advertising
pServer->getAdvertising()->start();
Serial.println("Waiting a client connection to notify...");
}
void loop() {
if (deviceConnected) {
pTxCharacteristic->setValue(&txValue, 1);
pTxCharacteristic->notify();
txValue++;
delay(10); // 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;
}
}
I can easily handle received data with this part of code
class MyCallbacks: public BLECharacteristicCallbacks {
String bleData;
void onWrite(BLECharacteristic *pCharacteristic) {
std::string rxValue = pCharacteristic->getValue();
if (rxValue.length() > 0) {
Serial.println("*********");
Serial.print("Received Value: ");
for (int i = 0; i < rxValue.length(); i++){
//Serial.print(rxValue[i]);
bleData=bleData+rxValue[i];
}
Serial.println();
Serial.println(bleData);
Serial.println("*********");
int first = bleData.indexOf(",");
String bleSSID = bleData.substring(0, first);
String blepw = bleData.substring(first+1, bleData.length());
Serial.println("Wifi : " + bleSSID + "," + "Password : " + blepw);
bleData="";
}
}
};
How to send data by using TxCharacteristic?
In my receiving code, I'm using this function to use callback.
if(pTxCharacteristic->canNotify()) {
pTxCharacteristic->registerForNotify(notifyCallback);
}
And here is my notifyCallback function i got from Google.
static void notifyCallback(
BLERemoteCharacteristic* pBLERemoteCharacteristic,
uint8_t* pData,
size_t length,
bool isNotify){
Serial.println(data);
}
It seems like i have to add a little function in notifyCallback.
However errors continue to occur. I can't get data. Tnx for help.