arduino turning on/off led using pySerial

Question

I am trying to communicate between arduino and pySerial but the serial monitor is giving me back weird characters so the arduino is not turning on/off led like it should. Thanks in advance.

Arduino code

int ledpin = 13;
int state; // 0 = led off, 1 = led on 
int flag = 0; // used so msg is only printed once
char val;

void setup(){
    pinMode(ledpin, OUTPUT);
    digitalWrite(ledpin, LOW);
    Serial.begin(9600); 
}

void loop(){
    //if data sent, read and save 
    if(Serial.available() > 0){
        state = Serial.read() -'0';
        val = char(state);
        Serial.println(val);
        flag = 0;
    }

    //if state = 0
    if (val == '0'){
        digitalWrite(ledpin, LOW);
        if(flag = 0){
            Serial.println('LED : Off');
            flag = 1;
        }
    }

    //if state = 1
    if (val = '1'){
        digitalWrite(ledpin,HIGH);
        if(flag = 0){
            Serial.println('LED : On');
            flag = 1;
         }
    }
}

Python code

import serial
from tkinter import *

port = '/dev/ttyACM0'
speed = 9600

def send_command(val):
connection = serial.Serial(port,speed)
connection.write(b"val")
connection.close()


#Create the window
win = Tk()

#Modify the root window
win.title("Arduino system") # gives title to window
win.geometry("320x100") # sets the size of the window

#Creating components
f = Frame(win) # creates window
#label with text
l = Label(win , text = "Flash LED")
b1 = Button(f, text ="Send 0")
b2 = Button(f, text ="Send 1")


#Defining methods
def but1(): send_command('0')  # command run if button 1 pressed
def but2(): send_command('1')  # command run if button 1 pressed
b1.configure(command = but1) # assiging methods to buttons
b2.configure(command = but2) # assiging methods to buttons



#Adding Components
l.pack() #packs in the label
b1.pack(side = LEFT) #packs the buttons in one after the other
b2.pack(side = LEFT) #packs the buttons in one after the other

f.pack()

win.mainloop() # start Gui

after sending a 0 from python to arduino the following appears on the serial monitor F 1 <

after sending a 1

the same thing appears

Udo Klein Udo Klein · Accepted Answer · 2015-01-12T11:54:44

The piece of code:

state = Serial.read() -'0';
val = char(state);
Serial.println(val);

will print a (char) 0 instead of a '0' and a (char) 1 instead of '1'. Also you compare val with character constants as if it was a character. However your code converts it to integer values that you store in a character.

→ You should make up your mind about what types your variables are and what you store in them.

In addition

Serial.println('LED : Off');

and

Serial.println('LED : On');

should most probably use " instad of ' quotation marks.

arduino turning on/off led using pySerial

1 Answers