ArduinoBLE subscribe() fails

s-lighte · February 7, 2026, 7:56pm

i try to write a basic arduino demo for BLE subscribe.
originally coming from

BluetoothLE with Arduino UNO R4 WiFi

opened 11:43PM - 06 Feb 26 UTC

Hello community, there is Bluetooth LE support already here 🥳 and i got the Bl…uetooth Classic working with some simple modules. now i have a new Arduino UNO R4 WiFi sitting on my Desk - and i tried to come up with an minimal example to control the onboard LED with DroidPad - and failed.. the App is giving the info on what UUID the U4 has to scann for. ([you can also find it in the code](https://github.com/UmerCodez/DroidPad/blob/main/app/src/main/java/com/github/umer0586/droidpad/data/connectionconfig/BluetoothLEConfig.kt#L9) [my sketch]() is mostly based on these sketches: - https://github.com/arduino-libraries/ArduinoBLE/blob/master/examples/Central/PeripheralExplorer/PeripheralExplorer.ino - https://docs.arduino.cc/learn/communication/bluetooth/#control-an-arduino-with-a-smartphone-app and the examples are all working. as fare as i have understand - DroidPad is advertising a service with one characteristics. i can connect and list successfully the characteristics - but as fare as [the *scanner*](https://github.com/Make-Your-School/mks-Arduino-UNO_R4_WiFi/blob/main/examples/dev/Bluetooth_LE_scann/Bluetooth_LE_scann.ino) sketch tells me - they are all not read write or subcribalbe. so no way to interact with them.. with the [Bluetooth_LE_scann.ino](https://github.com/Make-Your-School/mks-Arduino-UNO_R4_WiFi/blob/main/examples/dev/Bluetooth_LE_scann/Bluetooth_LE_scann.ino) i get this output: ``` Bluetooth® Low Energy Central - Peripheral Explorer Found 10:51:5d:49:d0:28 '' Found 10:55:44:33:22:27 'NWJ20210709010034' ffe0 Found 49:41:16:49:28:01 'FP4' 4fbfc1d7-f509-44ab-afe1-62ea40a4b111 Connecting ... Connected Discovering attributes ... Attributes discovered Device name: FP4 Appearance: 0x0 Service 0 :1801 Characteristic 2a05, properties 0x20, canSubscribe Descriptor 2803, value 0x0205003A2B Descriptor 2b3a, value 0x01 Characteristic 2b3a, properties 0x2, canRead, value 0x01 Descriptor 2803, value 0x0A0700292B Descriptor 2b29, value 0x00 Characteristic 2b29, properties 0xA, canRead, value 0x00, canWrite Descriptor 2803, value 0x0209002A2B Descriptor 2b2a, value 0x1A22311CB1EEA982039B84CB0F95A049 Characteristic 2b2a, properties 0x2, canRead, value 0x1A22311CB1EEA982039B84CB0F95A049 Service 1 :1800 Characteristic 2a00, properties 0x2, canRead, value 0x465034 Descriptor 2803, value 0x021800012A Descriptor 2a01, value 0x0000 Characteristic 2a01, properties 0x2, canRead, value 0x0000 Descriptor 2803, value 0x021A00A62A Descriptor 2aa6, value 0x01 Characteristic 2aa6, properties 0x2, canRead, value 0x01 Descriptor 2803, value 0x221C00882B Descriptor 2b88, value 0x Characteristic 2b88, properties 0x22, canRead, canSubscribe Descriptor 2902, value 0x Service 2 :4fbfc1d7-f509-44ab-afe1-62ea40a4b111 Characteristic dc3f5274-33ba-48de-8246-43bf8985b323, properties 0x10, canSubscribe Descriptor 2902, value 0x Service 3 :4fbfc1d7-f509-44ab-afe1-62ea40a4b111 Characteristic dc3f5274-33ba-48de-8246-43bf8985b323, properties 0x10, canSubscribe Descriptor 2902, value 0x Descriptor 2902, value 0x Service 4 :4fbfc1d7-f509-44ab-afe1-62ea40a4b111 Characteristic dc3f5274-33ba-48de-8246-43bf8985b323, properties 0x10, canSubscribe Descriptor 2902, value 0x Service 5 :4fbfc1d7-f509-44ab-afe1-62ea40a4b111 Characteristic dc3f5274-33ba-48de-8246-43bf8985b323, properties 0x10, canSubscribe Descriptor 2902, value 0x Disconnecting ... Disconnected ``` with [my example](https://github.com/Make-Your-School/mks-Arduino-UNO_R4_WiFi/blob/main/examples/dev/UNO_R4_WiFi-Bluetooth_DroidPad/UNO_R4_WiFi-Bluetooth_DroidPad.ino) i get this output: ``` 00:36:22.101 -> UNO_R4_WiFi-Bluetooth_DroidPad.ino 00:36:22.358 -> Bluethooth Device namens 'HackBLE' fertig initialisiert. 00:36:22.487 -> Gefunden: 'FP4' Service UUID '4fbfc1d7-f509-44ab-afe1-62ea40a4b111' 00:36:22.519 -> Verbinden ... 00:36:22.905 -> Verbunden 00:36:22.905 -> suche Attribute ... 00:36:28.205 -> Attribute gefunden 00:36:28.205 -> DroidPad characteristic nicht lesbar! 00:36:28.205 -> DroidPad characteristic nicht schreibbar! 00:36:28.205 -> DroidPad characteristic abonnierbar.. 00:36:33.250 -> subscription failed! ``` so i thought i have to do a subscription - as it is the only thing the characteristics offer(read is not allowed and write also not..) but that too fails.. seems i miss something entirely here 🤣 any tips / hints / links to a known working example are welcome :-)

DroidPad advertices itself as peripehral.
and the connection itself is all fine.
but i can not get it to work so i am able to successfully subscribe to receive the values..

my test-sketches can be found at

github.com/Make-Your-School/mks-Arduino-UNO_R4_WiFi

examples/dev/UNO_R4_WiFi-Bluetooth_DroidPad/UNO_R4_WiFi-Bluetooth_DroidPad.ino

main

// Extra benötigte Libraries:
// - ArduinoBLE

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// This Example is Work-In-Progress
// it currently does not work.
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#include <ArduinoBLE.h>

// dies sind die UUIDs die DroidPad verwendet.
// const char serviceUUID[] = ;
// const char characteristicUUID[] = ;

const int ledPin = LED_BUILTIN;

BLEDevice droidPadPeripheral;
bool droidPadConnected;

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and

github.com/Make-Your-School/mks-Arduino-UNO_R4_WiFi

examples/dev/Bluetooth_LE_scann/Bluetooth_LE_scann.ino

main

// https://docs.arduino.cc/tutorials/uno-r4-wifi/cheat-sheet/#bluetooth

#include <ArduinoBLE.h>

void setup() {
  delay(500);
  Serial.begin(115200);
  unsigned long timeStamp_Start = millis();
  while ((!Serial) && ((millis() - timeStamp_Start) < 6000)) {
    // warte bis der computer sich mit dem Arduino Seriell verbunden hat.
    // oder mache nach über 6s warten ohne Verbindung weiter.
    1;
  }
  delay(500);

  // begin initialization
  if (!BLE.begin()) {
    Serial.println("starting Bluetooth® Low Energy module failed!");

    while (1)

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(all based on the Library Examples)

any hints on what is going wrong here?

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ArduinoBLE subscribe() fails

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