How to communicate between two raspberry pi via Bluetooth and send sensor data from one pi to another?

Question

I'm working for some school project. I want to send temperature sensor data from one raspberry pi 4 to another pi 4 via Bluetooth. I searched a lot for tutorial but I didn't find any related tutorial. Please anyone help with this or any suggestions would be very helpful.

Answer 1

I know very little about Bluetooth and this answer may be dated or poor practice, but at least it works. If anyone knows better, please provide a better answer and I will delete this.

So, I have two Raspberry Pi 4 running Raspbian. I installed BlueDot on both with:

sudo pip3 install bluedot

I then paired them, running this on the first:

sudo bluetoothctl
[bluetooth]# discoverable on
[bluetooth]# pairable on
[bluetooth]# agent on
[bluetooth]# default-agent

and this on the second:

sudo bluetoothctl
[bluetooth]# discoverable on
[bluetooth]# pairable on
[bluetooth]# agent on
[bluetooth]# default-agent
[bluetooth]# scan on

When the first RasPi (hostname=pi4) showed up, I paired with it by typing this in the second RasPi:

[bluetooth]# pair DC:A6:32:03:0C:1B

Then I quit bluetoothctl on both.

Then I ran this server code (attributable to here) on the first RasPi UNDER sudo:

#!/usr/bin/env python3

from bluedot.btcomm import BluetoothServer
from time import sleep
from signal import pause

def data_received(data):
    print("recv - {}".format(data))
    server.send(data)

def client_connected():
    print("client connected")

def client_disconnected():
    print("client disconnected")

print("init")
server = BluetoothServer(
    data_received,
    auto_start = False,
    when_client_connects = client_connected,
    when_client_disconnects = client_disconnected)

print("starting")
server.start()
print(server.server_address)
print("waiting for connection")

try:
    pause()
except KeyboardInterrupt as e:
    print("cancelled by user")
finally:
    print("stopping")
    server.stop()
print("stopped")

And this code (attributable to here) on the second, also under sudo:

#!/usr/bin/env python3

from bluedot.btcomm import BluetoothClient
from datetime import datetime
from time import sleep
from signal import pause

def data_received(data):
    print("recv - {}".format(data))

print("Connecting")
c = BluetoothClient("pi4", data_received)

print("Sending")
try:
    while True:
        c.send("hi {} \n".format(str(datetime.now())))
        sleep(1)
finally:
    c.disconnect()

The two RasPis swapped messages successfully till interrupted. I measured the Round Trip Time (RTT) and it averaged around 30ms between two RasPi 4 placed around a metre apart.

It may be better to add the pi user to the dialout Linux group (or some other one) rather than run under sudo. If anyone knows, please say.