Writing to a Characteristic using the Android 4.3 API

[Alex Lynchosky]

I am having a lot of trouble using the new 4.3 Android API. I am trying to develop an application for the Android that will communicate via BLE to a Nordic device. I have based my application on the example UART project provided by Nordic:

www.nordicsemi.com/.../nRF-UART-2.0-for-Android-4.3

After analyzing this code, I thought that I had figured out how to successfully write to a characteristic. The function, "writeRXCharacteristic()" does exactly this. But when I used nearly identical code in my program, it is extremely inconsistent. I say inconsistent instead of not working because it DOES work sometimes. There are times when I can connect to the Nordic device, select the proper characteristic, and write to it. Albeit a not very fast transaction, but it works on occasion. But if I disconnect from the device, and reconnect, the write may or may not work. I have even completely re-installed the app, (without changing any code on the app or Nordic) and it has about ~20% of working. I have no idea why this could be happening. If anyone has any idea what this could be, please let me know! I have been having troubles with this for some time, and I can't find a pattern as to why it is so seemingly random.

Here is the code I am using to send the characteristic:

[b]public void writeCharacteristic(byte[] value) { BluetoothGattService LumService = mBluetoothGatt.getService(UUID_LUM_APP); if (LumService == null) { System.out.println("LumService null"); return; } BluetoothGattCharacteristic LumChar = LumService.getCharacteristic(UUID_LUM_CHAR); if (LumChar == null) { System.out.println("LumChar null"); return; } LumChar.setValue(value); boolean status = mBluetoothGatt.writeCharacteristic(LumChar); System.out.println("Write Status: " + status); }[/b]

If there is any additional information I can provide, please let me know. Thanks in advance!

[Hung Bui]

Hi Alex,

Sorry for a late reply. Could you give some more information on:

• Do you have the same problem with the nRF Uart app ?
• Which master device have you used to test ?
• What error code you have when writing is not successful? Did you have the characteristic null ?

[Alex Lynchosky]

Hung Bui,

I have already solved the problem. The example I was using did not have the write permissions on both the app side and the Nordic side. After I used the Nordic UART code on BOTH sides (Nordic and app), it worked much better. thank you for the response, and if I can answer anything else for you I will

[Ole Morten]

I'm answering this with the content of your comment above, Alex, just to clear up this question:

I have already solved the problem. The example I was using did not have the write permissions on both the app side and the Nordic side. After I used the Nordic UART code on BOTH sides (Nordic and app), it worked much better. thank you for the response, and if I can answer anything else for you I will

Thanks for letting us know the solution!

[Bastiaan]

hi, @Ole Morten I am also working on BLE using Android 4.3 api, i have used sample BLE app it is only reading charactaristics in DeviceScanActivity.activity but i want to write charactaristics by using button send so how can i use you above code to do this.. Basical i don't know the step by step procedure to write characteristics. Please help

[Guest]

hi, @Ole Morten I am also working on BLE using Android 4.3 api, i have used sample BLE app it is only reading charactaristics in DeviceScanActivity.activity but i want to write charactaristics by using button send so how can i use you above code to do this.. Basical i don't know the step by step procedure to write characteristics. Please help