Data transfer from sensor connected with I2C over Bluetooth NUS.

RE: Data transfer from sensor connected with I2C over Bluetooth NUS.

connorshannon — Thu, 07 Nov 2024 02:29:11 GMT

Hello, I know it's been a while since this thread has been active, but I'm having a similar issue. Esbriven, is there any chance you could share your completed code? I'm using a different board and sensor, but the general idea is the same and I can make the necessary changes to the code. Thanks!

RE: Data transfer from sensor connected with I2C over Bluetooth NUS.

Hung Bui — Thu, 08 Jun 2023 13:26:04 GMT

Hi Esbriven,

I don't see much point converting the data to human readable format then send over BLE.

Instead you send hex value over BLE and then convert to human readable format on the peer device, for example the app on the phone or the dongle.

On the peer you may want to look for "convert float to string" in the program language that you use on the peer.

For example in C: https://www.geeksforgeeks.org/gcvt-convert-float-value-string-c/

RE: Data transfer from sensor connected with I2C over Bluetooth NUS.

Esbriven — Thu, 08 Jun 2023 12:59:43 GMT

OK that's what i thought about the button.

I think managed to understand the bt_gatt_notify() function i'm able to send the data collected from my sensor, but they are in a hex format.

So now if I want to display the data on the central in a proper format (i.e float with some text like : AccX = %f g) what should I do ? If I understand properly the NUS protocol (with bt_nus_send() function) it recognize the data as ASCII and display it as such in the receiving end right ? Do I have to convert my data as a string prior the sending if I want to use this method ?

By the way I also have a nRF52840 dongle which could be programmed to convert the hex data send with the custom LBS explained in lesson 3 ex2 into a more readable format but I'm not sure if it's doable.

Thanks again for the response :)

RE: Data transfer from sensor connected with I2C over Bluetooth NUS.

Hung Bui — Thu, 08 Jun 2023 11:37:01 GMT

Hi Esbriven,

The "Button pressed" and "button releases" is just a feature in the app that it detect the LBS service automatically and translate 1 and 0 to "pressed" and "released".

When you use nRF Connect for mobile, and you declare your own service, it will display the hex value. For example:

RE: Data transfer from sensor connected with I2C over Bluetooth NUS.

Esbriven — Wed, 07 Jun 2023 14:58:23 GMT

Hi,

I have followed the exercise 2 and I managed to send data collected by my sensor but they are indeed in hex format. I've read that since it's binary data that are transmitted, the display has to be managed from the central (my phone with nRF Connect for mobile).

Another thing that I don't understand in the exercise 2 is how the message "button released" or "button pressed" are transmitted. I've notice that my phone get a notify with a value of 0x00 for "button released" and 0x01 for "button pressed" on top of the ASCII message. I searched in the different header files of zephyr to find a mention of both " button released" and "pressed" but i couldn't find any. Is it that nRF_connect (my phone) automatically recognized the value 0x00 as "button released" with the specific UUID related to the button or is it defined somewhere ?

Thank you for you response.

best regards.

RE: Data transfer from sensor connected with I2C over Bluetooth NUS.

Hung Bui — Wed, 07 Jun 2023 14:15:03 GMT

Hi Esbriven,

Have you gone through Lesson 4 exercise 2 ? In the exercise we show you how to send (simulated) sensor data using bt_gatt_notify().

It's similar to what the NUS service in peripheral_uart does. In the code you can find bt_nus_send() is called when there is some data in the UART buffer.
In your case you just need to call bt_gatt_notify() with the size of the data you want to send.
Note that you need to enable notification on the peer side (the phone) and if you are simply sending raw data it may not display as normal text as it's not ASCII you need to look into the raw data that you receive on the phone.