How to enable gatt indication/notification between Android and nrf51 devices?

[Mitch996]

Hello, I have walked through this tutorial:devzone.nordicsemi.com/.../ however things didn't work as planned. I can now read the default value of a value characteristic, but ble hvx does not work.

The part I think maybe problematic, and confusing at the same time is this:

" If you want you can enable notification right away, but since we have not yet set up any mechanisms updating the values nothing fancy will happen. Anyway, try to click the "Enable services" button. You should see that the value field of the CCCD is updated to 0x0001, meaning that notification is indeed enabled. You can also use the "Write" button and write to the CCCD manually."

I completely failed to follow here: Isn't all I have to do enable relevant fields on nrf51 device? Why do I have to enable anything related to cccd using MCP? Is the tutorial trying to tell me that there is a property on the attribute table of nrf51 but cannot be modified or enabled by nrf51 itself and MUST BE modified or enabled with a connected central/client device, like a PC, phone etc.?

If this is true, can some one tell me the proper java code or at least, a tutorial to enable proper cccd properties on an android phone? Since I couldn't find any at all.

Edit: I want to receive data FROM nrf51 TO android phone, I already can send data from phone to nrf51, but not the other way around.

[Hung Bui]

Hi,

It's just how BLE works. If a GATT client (in this case your phone) want to receive notification from the GATT server (your nRF51) it have to enable CCCD (write 0x01 to it) on the server. This is telling the server that "OK, I want to receive notification from you, you can send me whenever you want."

On Android, you enable CCCD by using [setCharacteristicNotification()](developer.android.com/.../BluetoothGatt.html, boolean)) .

I would suggest you to have a look at our example app, such as the nRF Blinky app or the nRF UART app.

[Mitch996]

Hello, will it be a problem that I setCharacteristicNotification() RIGHT BEFORE I send the data? See code below:

if ((charaProp | BluetoothGattCharacteristic.PROPERTY_NOTIFY) > 0) {
                        mNotifyCharacteristic = characteristic;
                        mBluetoothLeService.setCharacteristicNotification(
                                characteristic, true);
characteristic.setValue(data_to_write);

[Hung Bui]

I don't think any problem there. Note that you only setCharacteristicNotification() once after you get connected, you don't have to set it all the time.

characteristic.setValue(data_to_write); has nothing to do with enabling CCCD, they are 2 separated write command.

[Hung Bui]

You are right, Emil. I didn't spot that.