Raspberry Pi Serial Communication with Arduino with Python

Question

I want to communicate between my Raspberry Pi and Arduino using Python. So far the Arduino successfully sends a serial message to the Raspberry Pi and the message is read with the ser.readline() function in Python. But when I want to blink a led connected to my Raspberry Pi with an IF statement it won't work

The blink() function and everything else works but the code won't go into the IF statement that checks the ser.readline() value with a string variable

This is the code of my Arduino:

 String data="hello";

 void setup() {
 // put your setup code here, to run once:
 Serial.begin(9600);
 }

 void loop() {
 // put your main code here, to run repeatedly:
 Serial.println(data);//data that is being Sent
 delay(5000);
 }

And this is the Python code wich runs on my Raspberry Pi:

 import serial
 import RPi.GPIO as GPIO
 import time

 LedPin = 11    # pin11
 ser=serial.Serial("/dev/ttyUSB0",9600)  #change ACM number as found from ls /dev/tty/ACM*
 ser.baudrate=9600
 def setup():
    GPIO.setmode(GPIO.BOARD)       # Set the board mode to numbers pins by physical location
    GPIO.setup(LedPin, GPIO.OUT)   # Set pin mode as output
    GPIO.output(LedPin, GPIO.HIGH) # Set pin to high(+3.3V) to off the led

 def blink():
            print 'led on'
            GPIO.output(LedPin, GPIO.LOW)   # led on
            time.sleep(1.0)                 # wait 1 sec
            print 'led off'
            GPIO.output(LedPin, GPIO.HIGH)  # led off
            time.sleep(1.0)                 # wait 1 sec


 setup()
 while True:
    serialmessage = ser.readline()
    print("serial message is " + serialmessage)

if serialmessage == "hello":
    print("message recieved")
    blink()

This is what I see in the terminal: terminal_image

I've been searching for hours trying to find a solution but with no luck. I've also just started programming in Python. Thank you for your time.

Might be a good idea to test with a standard serial terminal app on the Pi just to check the link is working — Martin Beckett
Assuming the indentation shown here accurately reflects your source, your if statement and call to blink() aren't inside the while loop. They need to be indented. — larsks

Karen Simonyan Karen Simonyan · Accepted Answer · 2018-11-14T08:36:46

import serial                                                                                          
import RPi.GPIO as GPIO                                                                                
import time                                                                                            

LedPin = 11    # pin11                                                                                 
ser=serial.Serial("/dev/ttyUSB0",9600)  #change ACM number as found from ls /dev/tty/ACM*              
ser.baudrate=9600                                                                                      
def setup():                                                                                           
   GPIO.setmode(GPIO.BOARD)       # Set the board mode to numbers pins by physical location            
   GPIO.setup(LedPin, GPIO.OUT)   # Set pin mode as output                                             
   GPIO.output(LedPin, GPIO.HIGH) # Set pin to high(+3.3V) to off the led                              

def blink():                                                                                           
           print 'led on'                                                                              
           GPIO.output(LedPin, GPIO.LOW)   # led on                                                    
           time.sleep(1.0)                 # wait 1 sec                                                
           print 'led off'                                                                             
           GPIO.output(LedPin, GPIO.HIGH)  # led off                                                   
           time.sleep(1.0)                 # wait 1 sec                                                


setup()                                                                                                
while True:                                                                                            
   serialmessage = ser.readline()                                                                      
   print("serial message is " + serialmessage)                                                         

   if serialmessage == "hello":                                                                        
       print("message recieved")                                                                       
       blink()

Python uses spacing to detect blocks of code.

You need to put an if statement with a call to the blink method inside a while loop.

Also you can check incoming serial data by running command on Raspberry pi

sudo cat /dev/ttyUSB0

Raspberry Pi Serial Communication with Arduino with Python

1 Answers