simple blink led code question

Projects General Guidance
1

Hello. I wrote a very simple piece of code. all it does is when enter a 1 in serial monitor the the LED blinks for 1 second.

void setup()
{
  Serial.begin(9600);
  pinMode(12, OUTPUT);
}
 
void loop() {
  if (Serial.available()) {
    
    if(Serial.read()=='1') {
      digitalWrite(12, HIGH);
      delay(1000);
      digitalWrite(12, LOW);
      delay(1000);
    }  
  }
}

This code works just fine with the serial monitor.
Now I want to use python3 on my Mac instead of the Serial Monitor

import serial
#! /usr/local/bin/python3
 
import serial
from time import sleep

# for Mac
ser = serial.Serial("/dev/cu.usbmodem1D1330", baudrate=9600)

ser.write(('1').encode())

now the LED doesn't blink any more. I use the correct port /dev/cu.usbmodem1D1330 as in Ardrino. Can someone tell me what I have done wrong? Thanks

2

Connect your Mac to to the IDE serial monitor on the PC and see what it’s actually sending out

3

The Python code "ser.write(('1').encode())" sends the binary character b'00000001'. The Arduino code is looking for the ASCII coding of 1 which is b'00110001'

"ser.write('1')" or "ser.write(('00110001').encode())" might work better.

4 
ser.write ('1')
ser.flush()   # actually send it now
5

Thank you all for the replies. Unfortunately, none of the above suggestions work in my case.

@hammy "Connect your Mac to to the IDE serial monitor on the PC and see what it's actually sending out"
How do I do that? Every time the serial monitor open, when I run the python code, it always gives me an error "resource busy"

One thing I am very unclear is that on the Aduino side what data type I should give the ariduino serial monitor
to receive the data from python, int? char? byte?

and on the python3 side if I say ser.write('1'.encode()) in python3
what exactly the encode and should the arduino be set to receive, a char? an int? I tried both neither one works.

6

The problem comes from Python3 using Unicode for strings by default rather than using ASCII which is what the Arduino compiler is using.

To send the ASCII character for 1 you can explicitly use a bytes literal as follows:

ser.write(b'1')

Alternately you can specify the string and encode it as ASCII:

ser.write('1'.encode('ASCII'))

These are equivalent in that the following statement evaluates to True:

b'1' == '1'.encode('ASCII')

The data going over serial is just a single byte in this case so you should be able to put in any 8 bit data type on the Arduino side, so "char" or "byte" would work. Since it is ASCII data the convention would be to treat is as "char".

7

Duh! I feel so dumb! Took me a while to figure out, I forgot one silly thing. My code is like this now:
//Arduino side

#define LED 12

void setup() {
    pinMode(LED, OUTPUT);
    Serial.begin(9600);
}

void loop() {
  if (Serial.available()) {
    
    if(Serial.read()=='1') {
      digitalWrite(12, HIGH);
      delay(1000);
      digitalWrite(12, LOW);
      delay(1000);
    }  
  }
}

##python side

import serial
import time

ser = serial.Serial('/dev/cu.usbmodem1D1330', 9600)

time.sleep(2) #the sleep(2) is a must!!!!
ser.write('1'.encode())

It has neither to do with char, int nor encode(), I simply forgot that I need time.sleep(2) #the sleep(2) is a must!!!!
Lesson learned.