I'm trying to implement autoConnect between android app and Arduino ble

Question

I'm android developer and facing some autoConnect issue.

I'm using Arduino nano IOT and developed some simple application to communicate. but I don't know why autoConnect doesn't work in this case.

Arduino nano continuously sends gyroscope sensing data(but only when app connected to module)

below is sample code.

#include <ArduinoBLE.h>
#include <Arduino_LSM6DS3.h>

BLEService sensorService("66df5109-edde-4f8a-a5e1-02e02a69cbd5");
BLEStringCharacteristic xSensorLevel("741c12b9-e13c-4992-8a5e-fce46dec0bff", BLERead | BLENotify,15);
BLEStringCharacteristic ySensorLevel("baad41b2-f12e-4322-9ba6-22cd9ce09832", BLERead | BLENotify,15);
BLEStringCharacteristic zSensorLevel("5748a25d-1834-4c68-a49b-81bf3aeb2e50", BLERead | BLENotify,15);

// last sensor data
float oldXLevel = 0;
float oldYLevel = 0;
float oldZLevel = 0;
long previousMillis = 0;


void setup() {
 Serial.begin(9600);
 
 while (!Serial);
 
 if (!IMU.begin()) {
  Serial.println("Failed to initialize IMU!");
  while (1);
 }
 
 pinMode(LED_BUILTIN, OUTPUT);
 
 if (!BLE.begin()) {
  Serial.println("starting BLE failed!");
  while (1);
 }

 BLE.setLocalName("Demo Gyroscope");
 BLE.setAdvertisedService(sensorService);
 sensorService.addCharacteristic(xSensorLevel);
 sensorService.addCharacteristic(ySensorLevel);
 sensorService.addCharacteristic(zSensorLevel);
 BLE.addService(sensorService);

 BLE.advertise();
 Serial.println("Bluetooth device active, waiting for connections...");
}

void loop() {
 BLEDevice central = BLE.central();
 if (central) {
  Serial.print("Connected to central: ");
  Serial.println(central.address());
  digitalWrite(LED_BUILTIN, HIGH);

  while (central.connected()) {
   //long currentMillis = millis();
   updateGyroscopeLevel();
   delay(300);
  }

  digitalWrite(LED_BUILTIN, LOW);
  Serial.print("Disconnected from central: ");
  Serial.println(central.address());
 }
}

void updateGyroscopeLevel() {
 float x, y, z;
 if (IMU.gyroscopeAvailable()) {
  IMU.readGyroscope(x, y, z);
  if (x != oldXLevel) {
   xSensorLevel.writeValue(String(x));
   oldXLevel = x;
  }
 if (y != oldYLevel) {
  ySensorLevel.writeValue(String(y));
  oldYLevel = y;
 }
 
 if (z != oldZLevel) {
  zSensorLevel.writeValue(String(z));
  oldZLevel = z;
 }
 
 Serial.print(x);
 Serial.print('\t');
 Serial.print(y);
 Serial.print('\t');
 Serial.println(z);
 }
}

and in my android app, I have set autoConnect true

    private fun connectDevice(device: BluetoothDevice?) {
        // update the status
        broadcastUpdate(Actions.STATUS_MSG, "Connecting to ${device?.address}")
        bleGatt = device?.connectGatt(context, true, gattClientCallback)
    }

App can connect to module and read/write some data using UUID but when I turn off the module and turn on again, App cannot automatically connect it.

As far as I know, once I set it true, android store bt info as cache and trying to reconnect repeatedly. (fyi, I'm not using Service to maintain connection)

but in my case, when I turn the module on again, it just shows below message in serial monitor

Bluetooth device active, waiting for connections...

It seems like app doesn't retry to connect. I have read related questions and answers over here but couldn't find clue for my case.

My question over here is am I doing wrong? or this is normal behaviour? when it comes to bt earphone, it's automatically connected when turn on. so I'm thinking something like that.

Please share any idea for this.

Really appreciate it!

According to the docs *Whether to directly connect to the remote device (false) or to automatically connect as soon as the remote device becomes available (true).* you're doing ok. But I think as of API 31 the API is not doing its job well? — Kozmotronik, May 24 '22 at 13:55
Thanks for you comment, my pixel 3 is using Android Version 12(31). so do you think there's some connection issue on 31?? — ALAN, May 24 '22 at 14:04
Not a connection issue exactly but an issue with auto connection in particular. I haven't test it enough. But I will do it with different APIs to see whether it behaves similar on each. — Kozmotronik, May 24 '22 at 14:10
Meanwhile I suggest you to have a look at [this SO answer](https://stackoverflow.com/a/40187086/12749998) seems useful, it explains connection progress. — Kozmotronik, May 24 '22 at 14:17
Thanks, I have read the link it was helpful. I would really appreciate it if you share any result or idea once your investigation is done. I'll try more and add comment over here if I find any solution. Thanks. — ALAN, May 24 '22 at 14:24
Sure, I'll post an answer when I find out the what really problem is. — Kozmotronik, May 24 '22 at 14:40

score 1 · Accepted Answer · answered May 26 '22 at 14:35

After reading more articles, I found what's the issue.

Not sure if anyone reaching out to this question but in my case, I want app to reconnect to ble automatically even after turning off and on the ble.

But I found turning off/on the phone, turning off/on ble clear the cache in android internally. so Cannot automatically reconnect in this scenario.

Please have a look. this is really helpful for me

https://medium.com/@martijn.van.welie/making-android-ble-work-part-2-47a3cdaade07

score 0 · Answer 2 · answered May 24 '22 at 18:47

0

This is not an answer but I found autoConnect is working when I use nRF Connect application. that means BT module itself has no issue and my application has issue.

answered May 24 '22 at 18:47

ALAN

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I'm trying to implement autoConnect between android app and Arduino ble

2 Answers2