I am building an OBD Raspberry PI car dashboard and I've been struggling to get the adapter to connect and send info. I recently learned that the rfcomm support was dropped years ago by bluez and was suggested to use something like the bluedot library to establish serial connection with the adapter. I was wondering if any of y'all know of some tutorial or way that I can implement this into my current code for my project. For reference the link to the API I am talking about is: https://bluedot.readthedocs.io/en/latest/btcommapi.html The part with "connection = obd..." won't work because of a serial exception, so I am wondering how I can implement the bluetooth comm API from the library here to make it work.

The code for my project is:

import obd
from pygame.locals import *
import pygame

screen = pygame.display.set_mode((0, 0), pygame.FULLSCREEN)

connection = obd.Async("/dev/rfcomm0", protocol="6", baudrate="9600", fast=False, timeout = 30)

#Continuously query until the amount of supported commands is greater than 100
while len(connection.supported_commands) < 100:
    connection = obd.Async("/dev/rfcomm0", protocol="6", baudrate="9600", fast=False, timeout = 30)

WHITE = (255, 255, 255)
BLACK = (0, 0, 0)

#Initial values for speed, rpm, and load
speed = 0
rpm = 0
load = 0

#Method used to draw our graphics to the screen
def draw_screen():
    pygame.draw.rect(screen, WHITE, pygame.Rect(5, 5, 150, 150), 2)
    pygame.draw.rect(screen, WHITE, pygame.Rect(270, 5, 150, 150), 2)
    pygame.draw.rect(screen, WHITE, pygame.Rect(155, 100, 115, 115), 2)
    speedF = pygame.font.SysFont(None, 50)
    speedText = speedF.render("Speed", True, WHITE)
    screen.blit(speedText, (15, 160))
    rpmF = pygame.font.SysFont(None, 50)
    rpmText = rpmF.render("RPM", True, WHITE)
    screen.blit(rpmText, (310, 160))
    loadF = pygame.font.SysFont(None, 50)
    loadText = loadF.render("Load", True, WHITE)
    screen.blit(loadText, (175, 60))

#Commands to query for data
c1 = obd.commands.SPEED  
c2 = obd.commands.RPM
c3 = obd.commands.ENGINE_LOAD

#Tracks the values of speed, rpm, and load since they will be constantly changing as you drive
def speedTracker(s):
    global speed
    if not s.is_null():
        speed = int(s.value.magnitude * .621)
def rpmTracker(r):
    global rpm
    if not r.is_null():
        rpm = int(r.value.magnitude)

def loadTracker(l):
    global load
    if not l.is_null():
        load = int(l.value.magnitude)

#Watches the data extracted by the obd adapter        
connection.watch(c1, callback=speedTracker)
connection.watch(c2, callback=rpmTracker)
connection.watch(c3, callback=loadTracker)
running =  True

#Pygame loop which displays our graphics as well as our speed, load, and rpm values
while running:
    for event in pygame.event.get():
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_ESCAPE:
                running = False
    speedFont = pygame.font.SysFont(None, 50)
    speedTxt = speedFont.render(str(speed) + " mph", True, WHITE)
    rpmFont = pygame.font.SysFont(None, 75)
    rpmTxt = rpmFont.render(str(rpm), True, WHITE)
    loadFont = pygame.font.SysFont(None, 75)
    loadTxt = speedFont.render(str(load) + "%", True, WHITE)
    screen.blit(speedTxt, (22, 50))

    screen.blit(rpmTxt, (285, 50))
    screen.blit(loadTxt, (172, 130))
  • rfcomm hci0 connect 11:22:33:44:55:66 1 & FOLLOWED BY CTL-C still works on my Pi4 to set up /dev/rfcomm0. You have to guess the channel number (probably 1 as here). Read/write data through /dev/rfcomm0 as a file. Bluedot is no use for this.
    – petzval
    Dec 9, 2023 at 17:25
  • The pyodb library appears to be expecting a "serial" port (e.g ("/dev/rfcomm0") to be given to it. BlueZ has deprecated output to a a serial port and instead uses sockets. This means you have to either create a bt_socket to serial bridge or workout how pyodb can work with sockets. FYI: Bluedot uses pygame for its app (github.com/martinohanlon/BlueDot/blob/master/bluedot/app.py).
    – ukBaz
    Dec 10, 2023 at 15:21


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