nrf51 - Writing 'text' on characteristic doesn't work using nrfConnect

[tehreem]

Hi,

I am developing an application that needs to communicate with nrf51 module over BLE. Specifically I need to write a string on a given characteristic but unable to do so on an example code.

While debugging my code using nrf Connect mobile app I noticed that I'm not able to write 'text' on the characteristic at all (doesn't hit on_write breakpoint). But if I try byte/byte array, it does get hit.

I'm assuming I need to declare the characteristic type to accept string in some way? I'm not sure how to do that though. Here is my code declaring characteristics:

#define CUSTOM_SERVICE_UUID_BASE         {0xBC, 0x8A, 0xBF, 0x45, 0xCA, 0x05, 0x50, 0xBA, \
                                          0x40, 0x42, 0xB0, 0x00, 0xC9, 0xAD, 0x64, 0xF3}

#define CUSTOM_SERVICE_UUID               0x1400
#define CUSTOM_VALUE_CHAR_UUID            0x1401

Can anyone point me to a beginner's tutorial where I can learn this stuff?

Thanks

[Vidar Berg]

Hello,

Have you checked if the characteristic is initialized with the .max_len paramater set to more than 1? Also, are you testing nRF connect on Android or iOS?

Best regards,

Vidar

[tehreem]

Thank you, that worked. However, I'm still not able to set the length to more than 20 characters. Is that a limitation? This is how I'm setting it:

attr_char_value.init_len  = sizeof(char);
attr_char_value.init_offs = 0;
attr_char_value.max_len   = 30 * sizeof(char);

But it only accepts first 20 characters. I'm using nRF Connect on Android.

[Vidar Berg]

The max length is usually limited by the ATT MTU size, which is 23 bytes by default (payload = MTU size - 3 byte overhead). Some of the SDK examples such as the UART/Serial Port Emulation over BLE use the GATT Module to negoitate a longer MTU with the client.