BLE Notification example: ESP32 BLE server read analog input and notify connected device

Code run on ESP32-DevKitC V4 (Arduino framework), to act as BLE server. Once connected, it read Analog Input and notify connected device.

It's modified from last post of ESP32 BLE_notify example.

The client side is programmed using Python run on Raspberry Pi, handle the notification and plot the value graphically.

BLE_notify_AIN.ino

#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>

#define PinAnalogIn 36

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"

bool rqsNotify;
unsigned long prvMillis;
#define INTERVAL_READ 1000
int valNotify;
#define MAX_VALNOTIFY 255

int ain = 0;

class MyServerCallbacks: public BLEServerCallbacks {
    void onConnect(BLEServer* pServer) {
      deviceConnected = true;

      rqsNotify = false;
      prvMillis = millis();
      Serial.println("Device connected");
    };

    void onDisconnect(BLEServer* pServer) {
      deviceConnected = false;
      rqsNotify = false;
      Serial.println("Device disconnected");
    }
};

void prcRead(){
  if(deviceConnected){
    unsigned long curMillis = millis();
    if((curMillis-prvMillis) >= INTERVAL_READ){
      int valAIO = analogRead(PinAnalogIn);
      valNotify = map(valAIO, 0, 4096, 0, 255);
      Serial.println(valNotify);
      
      rqsNotify = true;
      prvMillis = curMillis;
    }
  }
  
}


void setup() {
  Serial.begin(115200);

  // Create the BLE Device
  BLEDevice::init("ESP32");

  // 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) {
        if(rqsNotify){
          rqsNotify = false;
          //pCharacteristic->setValue((uint8_t*)valNotify, 1);
          //pCharacteristic->notify();

          value = valNotify;

          pCharacteristic->setValue((uint8_t*)&value, 4);
          pCharacteristic->notify();
          //value++;
          
        }
    }
    // 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;
    }

    prcRead();
}