python 3.x - BLE communication between two Raspberry Pi 4

Question

I am collecting pressure sensor data from 4 Arduino Nano 33 ble to a raspberry pi 4. I am able to receive the data from all the sensors. Now, I want to send this received data to another Raspberry Pi 4 using BLE communication in real-time such that the first Raspberry Pi acts as a repeater. I searched but could not find a suitable approach or solution to implement this. The first Raspberry Pi could act as a peripheral/client sending all the received sensor data and the second raspberry pi could act as a central/server to receive all the sensor data which can be further displayed on web interfaces or stored in a database.

I tried connecting initially with one Arduino and sending its data over raspberry Pi. I have written the code for Raspberry Pi Client and Server using Bluedot library in Python.

Raspberry Pi 4 Client code

import sys
import time
from bluepy import btle
from bluedot.btcomm import BluetoothClient
from signal import pause

def data_3():
    mac_adrs3 = 'f3:9a:9a:e8:54:5c'
    
    print("Connecting..")
    tp3_sense = btle.Peripheral(mac_adrs3)
    
    print("Discovering Services..")
    _=tp3_sense.services
    tire3_sensing_service = tp3_sense.getServiceByUUID("2b7537ab-8899-4359-a78a-096e076a4605")
    
    print("Discovering characteristics..")
    _= tire3_sensing_service.getCharacteristics()
    
    return tire3_sensing_service

def byte_array_to_int(value):
    value = bytearray(value)
    value = int.from_bytes(value, byteorder='little')
    return value

def byte_array_to_char(value):
    value = value.decode("utf-8")
    return value

def decimal_exponent_two(value):
    return value/100

def decimal_exponent_one(value):
    return value/10

def pascals_to_kilopascals(value):
    return value / 1000

def read_pressure3(service3):
    pres3_char = service3.getCharacteristics("9c30d6b2-e3d3-4eae-8641-425a36d550ec")[0]
    pres3 = pres3_char.read()
    pres3 = byte_array_to_int(pres3)
    #pres3 = decimal_exponent_one(pres3)
    #pres3 = pascals_to_kilopascals(pres3)
    print(f"Barometric pressure 3 : {round(pres3,2)} kPa")
    return pres3

def read_temperature3(service3):
    temp3_char = service3.getCharacteristics("e986145c-ead6-41a7-9718-d2b0b4834a11")[0]
    temp3 = temp3_char.read()
    temp3 = byte_array_to_int(temp3)
    #temp3 = decimal_exponent_two(temp3)
    print(f"temperature 3 : {round(temp3,2)}  C")
    return temp3

def loop():
    c = data_3()
    while True:
        time.sleep(1.0)
        print("
")
        read_temperature3(c)
        read_pressure3(c)
        
        t3 = read_temperature3(c)
        p3 = read_pressure3(c)
        
        r = BluetoothClient("DC:A6:32:4C:9D:ED", data_received_callback=None, port=2)
        r.send(f"temp 3 : {t3} ")
        r.send("
")
        r.send(f"pressure 3 : {p3} ")
        
        #pause()
        
        #time.sleep(1.0)

def main():
    loop()
    
if __name__ == "__main__":
    main()
        

Raspberry Pi Server code

from bluedot.btcomm import BluetoothServer
from signal import pause

def data_received(data):
    print(data)
    s.send(data)

s = BluetoothServer(data_received)
pause()

I am able to receive two readings and after that the client disconnects with the below error.

pi@raspberrypi:~/Desktop/rpible $ python3 onearduino_senddata.py 
Connecting..
Discovering Services..
Discovering characteristics..


temperature 3 : 0  C
Barometric pressure 3 : 100 kPa


temperature 3 : 0  C
Barometric pressure 3 : 100 kPa
Traceback (most recent call last):
  File "onearduino_senddata.py", line 83, in <module>
    main()
  File "onearduino_senddata.py", line 80, in main
    loop()
  File "onearduino_senddata.py", line 70, in loop
    r = BluetoothClient("DC:A6:32:4C:9D:ED", data_received_callback=None, port=2)
  File "/usr/local/lib/python3.7/dist-packages/bluedot/btcomm.py", line 567, in __init__
    self.connect()
  File "/usr/local/lib/python3.7/dist-packages/bluedot/btcomm.py", line 660, in connect
    self._client_sock.connect((server_mac, self._port))
OSError: [Errno 16] Device or resource busy

please help to solve this issue.

question from:https://stackoverflow.com/questions/65935999/ble-communication-between-two-raspberry-pi-4

Answer 1

Found the solution.

Create the client once outside the while loop and then the data transfer happens.

updated loop function.

def loop():
    c = data_3()
//create the client connection here
    r = BluetoothClient("DC:A6:32:4C:9D:ED", data_received_callback=None) 
 
    while True:
        time.sleep(1.0)
        print("
") 
        t3 = read_temperature3(c)
        p3 = read_pressure3(c)
        
        
        r.send(f"temp 3 : {t3} ")
        r.send("
")
        r.send(f"pressure 3 : {p3} ")