Help creating a data logging app

I have an Android 6 phone with an external SD card.
I am trying to develop an app which reads an external accelerometer using Bluetooth (done) does some calculations and save that and the raw XYZ values to a CSV file on the phones sd card which can be seen and transferred in explorer to my PC for Excel.
I have tried various methods of writing to the sd card, it seems successful because I can read from them in my app but I cannot see them in Explorer.
Any advice please on how to achieve this.

this extension probably can help
SMB Manager Extension by Jörg Hüneburg to list all files and folders of smb share (windows shared folder) and to copy a local file to smb share


Chech the image in this post its about using Bluetooth with external devices like arduino

Thanks for responding.
I am able to receive the Bluetooth data into CSV format and it appears to save to a file because I can usually read it back in my app.
The problem is I want to be able to see that file and be able to copy or share it to my PC using an explorer on my PC or on the phone.
I need to save the files to the external SD because my phone is old and has limited storage space and the files are large.
I get the same response whether I use the companion or installed .apk on phone.
If I use:

blocks (14)

I always get “Dir Exists” and with the global “PathOnly”/“Path_FileName” set to :

FileName=“JimsData/Button8_102454.txt” I get phone warning “could not be created”.

FileName="/JimsData/Button9_103601.txt" visible in phones internal storage at /JimsData.

FileName="/storage/sdcard1/JimsData/Button4_100258.txt" my app reads/writes to it but I cant find it.

FileName="/storage/6329-131C/JimsData/Button6_100258.txt" my app reads/writes it but I cant find it.

PS. I have a Bluetooth terminal app in which I can save to SD card and then copy over to windows using a File Explorer.
Any further advice please.

If you are interested:
JimsFileSaveTest_Simple (2).aia (681.3 KB)

Any advice would be welcome.