Issues connecting and printing to BLE device

I have a POS terminal with a built-in printer and am having some issues connecting and printing consistently.

Firstly, as an FYI, as I posted in another thread, I have found out that the MAC address can be used to connect to the device (@matt_conroy can you get Thunkable to update the documentation to include this please).

My app accepts information from the user, retrieves data from a database and then creates an output which I want to print.

If I run these blocks in a screen on its own, I can get the printer to connect and print -

However, if I call this screen from another, I either get an error that the device is not connected or that the “Can’t write the characteristic provided.”

I would be grateful for any advice.

Thanks and Happy Holidays from Barbados,

1 Like

Throw your send message block in the connect blocks then do section

Hi. This made no difference. Going directly to the connect and print screen works but going through the 4 screens before give me the Can’t write error.

How about removing spaces

Which spaces?


Sounds like a bug.


If you have the connection occur on the first screen of the app it works,


If you add a new screen as the first screen that only and immediately redirects you to the screen that connects, the connection fails? Or the write action only fails?

Sometimes it is the connection, other times the writing.

@ioannis @matt_conroy Would you be able to shed some light on this issue?


Sure, trying to make sure I have it correct. Can you check this app and let me know if it correctly replicates the scenario where you are having this issue?

Screen1: One second delay and then navigate to Screen2
Screen2: Click event to connect to device by device ID. 2nd click event to go to Screen3.
Screen3: Transmit string to device.

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