Communication of One Central Device and More than One Peripheral Device

[vyohai]

Does the library support connection and communication between one central device and more than one peripheral device?
And how could it be implemented?

[polldo]

Hi @vyohai ,
yes, it is possible.
Each central device can be connected to more peripherals and each peripheral can be connected to more centrals.
However, at the moment the library doesn't expose the functions to retrieve the connected devices, so the handling of multiple devices must be done at application level.
To deal with this I've implemented some possible functions that allow to loop through all the connected devices. You can see it here #105 , let me know what you think could be added or improved.
Here are two examples of how to use these additional functions to manage multiple connected devices.

--- Peripheral device handling more centrals:

#include <ArduinoBLE.h>

BLEService batteryService("180F");
BLEUnsignedCharCharacteristic batteryLevelChar("2A19", BLERead | BLEWrite); 

void setup() {
  Serial.begin(115200);    
  pinMode(LED_BUILTIN, OUTPUT); 
  // Start BLE
  if (!BLE.begin()) {
    Serial.println("starting BLE failed!");
    while (1);
  }
  BLE.debug(Serial);

  // Configure peripheral
  BLE.setLocalName("peripheral");
  BLE.setAdvertisedService(batteryService); 
  batteryService.addCharacteristic(batteryLevelChar); 
  BLE.addService(batteryService);
  BLE.advertise();

  Serial.println("peripheral configured - central connected: 0");
}

void loop() {
  BLE.poll();
  // Led on if some central is connected
  if (BLE.centralCount() > 0) {
    digitalWrite(LED_BUILTIN, HIGH);
  } else {
    digitalWrite(LED_BUILTIN, LOW);
  }

  // Check number of connected devices and enable advertising
  static auto timeRef = millis();
  if (millis() - timeRef >= 5000) {
    timeRef = millis();
    auto count = BLE.centralCount();
    Serial.print("Central count: ");
    Serial.println(count);
    if (count < 3) {
      BLE.advertise();
    }
  }
}

--- Central device handling more peripherals:

#include <ArduinoBLE.h>

void setup() {
  Serial.begin(115200);
  BLE.begin();
  BLE.scanForName("peripheral");
}

void connectionLoop() 
{
  // If not already connected to 2 peripherals, try to connect to a new found peripheral.
  if (BLE.peripheralCount() < 2) {

    BLEDevice peripheral = BLE.available();
    if (peripheral) {
      BLE.stopScan();

      if (!peripheral.connect()) {
        Serial.println("Failed to connect!");
        return;
      }

      if (!peripheral.discoverAttributes()) {
        Serial.println("Attribute discovery failed!");
        peripheral.disconnect();
        return;
      }
    }
  }
}

auto timeRef = millis();
void loop() {
  connectionLoop();

  if (millis() - timeRef >= 5000) {
    timeRef = millis();

    int periphCount = BLE.peripheralCount();
    Serial.print(" Peripheral connected: ");
    Serial.println(periphCount);

    if (periphCount < 2) {
      BLE.scanForName("peripheral");
    }

    // Loop through all connected peripherals
    for (int periphIdx = 0; periphIdx < periphCount; periphIdx++) {
      BLEDevice peripheral = BLE.peripheral(periphIdx);
      if (peripheral) {
        BLECharacteristic batteryLevelChar = peripheral.characteristic("2A19");

        if (!batteryLevelChar) {
          Serial.println("Peripheral does not have battery level characteristic!");
          peripheral.disconnect();
        } else {
          Serial.print("Peripheral connected, value: ");
          batteryLevelChar.read();
          Serial.println(*batteryLevelChar.value());
        }
      }
    }
  }
}

[vyohai]

Hi Polldo
thank you for all of your work
the example code doesn't work.
the error is :
'class BLELocalDevice' has no member named 'peripheralCount'
and in general when I try to scan for 2 peripherals and then connect to them one by one the 2nd one can't connect.
could that work?
am I doing something wrong?

[polldo]

@vyohai to compile the example you should checkout the multi-connection branch: https://github.com/arduino-libraries/ArduinoBLE/tree/multi-connection
Also, are you using a nano 33 ble? In that case there is an open issue that addresses the problem of connecting a central to many peripherals #108

[vyohai]

thank you it seems like it's working

[sprasadkrish]

Hi Polldo
thank you for all of your work
the example code doesn't work.
the error is :
'class BLELocalDevice' has no member named 'peripheralCount'
and in general when I try to scan for 2 peripherals and then connect to them one by one the 2nd one can't connect.
could that work?
am I doing something wrong?

thank you it seems like it's working

Hi @vyohai
how you solved this issue , i am also facing same kind of issue .

[polldo]

Hi @sprasadkrish ,
can you describe the issue you are facing?
Have you tried this #50 (comment) ?
Also, if you are using a nano33ble have a look at this #108
Thanks

[sprasadkrish]

Hi @sprasadkrish ,
can you describe the issue you are facing?
Have you tried this #50 (comment) ?
Also, if you are using a nano33ble have a look at this #108
Thanks

Hi @vyohai
Thank you , my issue : MKR1010 BLE - Timeout issue #109
i tried above code , but only one device connecting .