M5Stack | M5Stack Arduino Library | Runtime Evironment library

The specification you provided shows the correct flow of messages needed to start streaming. You have to start by requesting the streaming settings first.

For requesting the ppi settings just send 0x01 0x03 to the P=MD control point.

While looking at the source code of the polar-ble-sdk I found this in BlePMDClient.java (I added comments to the relevant parts):

I believe your current situation and your goal as follows.

• Your value of postdata.sensor.a is correct value you expect.
• You want to put the value of postdata.sensor.a to a cell and you want to create a chart of gauge type (this is from like a meter?).

• From your script, I would like to propose to use 2 sheets. One is a log sheet which is append the values of sheet.appendRow([date_time,postdata.sensor.a]); as a log. Another is a chart sheet which shows a gauge chart using the current value.

When above points are reflected to your script, it becomes as follows.

Before you use this script, please set your Spreadsheet ID and the maximum and minimum values for the gauge chart you expect.

There are a number of layers that are used in the communication process and depending where you tap into that stack will depend what coding you need to do. The other complication is that BlueZ (the Bluetooth stack on linux) changed how it works over recent times leaving a lot of out of date information on the internet and easy for people to get confused.

With two Bluetooth devices, they need to establish a pairng. This is typically a one off provisioning step. This can be done with tools like Blueman or on the command line with bluetoothctl. Once you have a pairing established between your RPi and the M5Stack Stick, you shouldn't need to discover nearby devices again. Your script should just be able to connect if you tell it which device to connect to.

The M5Stack stick is advertising as having a Serial Port Profile (SPP). This is a layer on top of rfcomm.

There is a blog post about how this type of connection can be done with the standard Python3 installation: http://blog.kevindoran.co/bluetooth-programming-with-python-3/

My expectation is that you will only have to do the client.py on your RPi as the M5Stack Stick is the server. You will need to know its address and which port to connect on. Might be some trial and error on the port number (1 and 3 seem to be common).

Another library that I find helpful for SPP, is bluedot as it abstracts away some of the boilerplate code: https://bluedot.readthedocs.io/en/latest/btcommapi.html#bluetoothclient

So in summary, my recommendation is to use the standard Python Socket library or Bluedot. This will allow you to specify the address of the device you wish to connect to in your code and the underlying libraries will take care of making the connection and setting up the serial port (as long as you have already paired the two devices).

Example of what the above might look like with Bluedot