Simple Bluetooth Controlled Car – Raspberry Pi Pico

Now that you have made all the necessary connections. We can program Pico. All the code for this project is available on GitHub. We will cover the code on the Pico first, then look at the Android Application.

We start by importing all the libraries and modules we need.

from machine import Pin,PWM,UART #importing PIN and PWM
import time #importing time

We can set up our Baud rate (The baud rate is the rate at which information is transferred in a communication channel.)

#Defining UART channel and Baud Rate
uart= UART(0,9600)

We set up all the pins connected to the L298n motor driver in this code block. We define the frequency of our PWM and set the maximum cycle of 65025, which we will control with a thumb slider on our App.

#OUT1 and OUT2
In1=Pin(6,Pin.OUT) #IN1
In2=Pin(7,Pin.OUT) #IN2
#OUT3 and OUT4
In3=Pin(4,Pin.OUT) #IN3
In4=Pin(3,Pin.OUT) #IN4
# Set PWM
EN_A=PWM(Pin(8))
EN_B=PWM(Pin(2))
# Defining frequency for enable pins
EN_A.freq(1500)
EN_B.freq(1500)
# Setting maximum duty cycle for maximum speed (0 to 65025)
EN_A.duty_u16(65025)
EN_B.duty_u16(65025)

We then create five functions to control the movement and direction of the car in which we control the pins to either be high or low. This will control the direction the motor is turning in. If your robot does not turn in the right direction you either have to swop the cables from the motor to the L298n driver or change the high and low in the code below.

# Left
def turn_left():
  In1.high()
  In2.low()
  In3.low()
  In4.high()
   
# Right
def turn_right():
  In1.low()
  In2.high()
  In3.high()
  In4.low()
   
# Backward
def move_backward():
  In1.low()
  In2.high()
  In3.low()
  In4.high()
   
# Forward
def move_forward():
  In1.high()
  In2.low()
  In3.high()
  In4.low()
   
# Stop
def stop():
  In1.low()
  In2.low()
  In3.low()
  In4.low()

In our main loop, we constantly check the Bluetooth to see what button is pressed by looking at the data received from our App once the button is pressed. The relevant function will be executed depending on the data received through Bluetooth. We also check what the speed is set at, and if nothing is being sent through, the default function is called will be stopped.

while True:
  if uart.any(): #Checking if data available
    data=uart.read() #Getting data
    data=str(data) #Converting bytes to str type
    print(data)
    if('forward' in data):
      move_forward() #Forward
    elif('backward' in data):
      move_backward() #Backward
    elif('right' in data):
      turn_right() #Turn Right
    elif('left' in data):
      turn_left() #Turn Left
    elif('stop' in data):
      stop() #Stop
    elif('E' in data):
      speed=data.split("|")
      print(speed[1])
      set_speed = float(speed[1])/100 * 65025
      EN_A.duty_u16(int(set_speed)) #Setting Duty Cycle
      EN_B.duty_u16(int(set_speed)) #Setting Duty Cycle
    else:
      stop() #Stop

This is all the code needed for the Pico; now, we need to create a simple mobile App, and we will be using MIT App inventor to make an android application.

Step 5: Android App (MIT App Inventor)

MIT App Inventor is a web application integrated development environment originally provided by Google, and now maintained by the Massachusetts Institute of Technology.

We create a simple interface where you can connect to the Bluetooth module by selecting a device and have the buttons to control the movement and the slider for the speed.

For the blocks, we check what button is pressed, and depending on which button is, we will send a text which our Pico will execute by calling the correct function to control the car. If we let go of the button, it will call the stop function.

Once the App is on your phone, connect to the robot car and have some fun.

I have included the original .aia file in case you want to change the App and make your changes, and the apk if you want to use the App as is.

Step 6: Conclusion and Improvement