Unable to get Notify data using Noble

Question

Can't receive any notifications sent from the Server peripheral.

I am using ESP32 as Server with the "BLE_notify" code that you can find in the Arduino app (File> Examples ESP32 BLE Arduino > BLE_notify). With this code the ESP32 starts notifying new messages every second once a Client connects. The client used is a Raspberry Pi with Noble node library installed on it (https://github.com/abandonware/noble). this is the code I am using.

    noble.on('discover', async (peripheral) => {
      console.log('found peripheral:', peripheral.advertisement);
      await noble.stopScanningAsync();
      await peripheral.connectAsync();
      console.log("Connected")

      try {
        const services = await peripheral.discoverServicesAsync([SERVICE_UUID]);
        const characteristics = await services[0].discoverCharacteristicsAsync([CHARACTERISTIC_UUID])
        const ch = characteristics[0]
        
        ch.on('read', function(data, isNotification) {
          console.log(isNotification)
          console.log('Temperature Value: ', data.readUInt8(0));
        })
        
        ch.on('data', function(data, isNotification) {
          console.log(isNotification)
          console.log('Temperature Value: ', data.readUInt8(0));
        })
        ch.notify(true, function(error) {
          console.log(error)
          console.log('temperature notification on');
        })
      
      } catch (e) {
        // handle error
        console.log("ERROR: ",e)
      }
    });

SERVICE_UUID and CHARACTERISTIC_UUID are obviously the UUIDs coded in the ESP32.

This code sort of works, it can find Services and Characteristics and it can successfully connect to the peripheral, but it cannot receive messages notifications. I also tried an Android app that works as client, from that app I can get all the messages notified by the peripheral once connected to it. So there is something missing in the noBLE client side.

I think there is something wrong in the on.read/on.data/notify(true) callback methods. Maybe these are not the methods to receive notifications from Server? I also tried the subscribe methods but still not working.

The official documentation is not clear. Anyone could get it up and running? Please help.

Answer 1

on.read/on.data/ are event listeners. There is nothing wrong with them. They are invoked when there is a certain event.

For example adding characteristic.read([callback(error, data)]); would have invoked the on.read.

From the source:

Emitted when:

• Characteristic read has completed, result of characteristic.read(...)
• Characteristic value has been updated by peripheral via notification or indication, after having been enabled with characteristic.notify(true[, callback(error)])

Answer 2

I resolve using the following two envs NOBLE_MULTI_ROLE=1 and NOBLE_REPORT_ALL_HCI_EVENTS=1 (see the documentation https://github.com/abandonware/noble)