Python Serial Writes to Arduino is different from Arduino's Serial Monitor's Serial Writes

Question

I have a Python script that writes a string test to the Arduino serial port. If the arduino receives the test string, it should reply with a string ok and LED 13 should like up..

Problem: When the Arduino Serial Monitor is used to write test to serial port, Arduino replies with ok as expected and the LED #13 lights up.

However when the Python script writes test to the same serial port, nothing happens. Arduino does not reply to serial port and the LED #13 does not light up.

Any ideas how Python script can be fixed to get the ok response from Arduino and LED 13 to light up?

Arduino Sketch

int ledPin = 13;


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


void loop() {

    while(Serial.available() == 0) { }
    
    if(Serial.readString() == "test\r\n") {
      Serial.print("ok\r\n");
      digitalWrite(ledPin, HIGH);
    } 
    
    readString = ""; // Clear recieved buffer
    delay(100);
}

Python Script

port = 'COM5'
ser = serial.Serial(
    port=port,
    baudrate=9600,
    timeout=5
)

serial.write("test\r\n")

response = serial.readline()
print response

Joran Beasley · Accepted Answer · 2016-09-12 18:40:56Z

2

port = 'COM5'
ser = serial.Serial(
    port=port,
    baudrate=9600,
    timeout=5
)

# you need to sleep after opening the port for a few seconds
time.sleep(5) # arduino takes a few seconds to be ready ...

#also you should write to your instance
ser.write("test\r\n")
# and give arduino time to respond
time.sleep(0.5)
response = self.serial.readline()
print response

if you dont want to wait a fixed number of seconds you probably need to wait for ser.cts (clear to send)

edited Sep 12, 2016 at 18:40

answered Sep 12, 2016 at 18:37

Joran Beasley

114k13 gold badges167 silver badges187 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Nyxynyx Over a year ago

Works!! Spent over an hour trying encoding of string and stuff lol

Joran Beasley Over a year ago

I have had lottttts of experience with python + serial + ardiuno ;P

Nyxynyx Over a year ago

Awesome! A related question: In an infinite loop in Python, it takes about a second for Arduino to reply with ok after sending test. Is there a way to speed this up?

Collectives™ on Stack Overflow

Python Serial Writes to Arduino is different from Arduino's Serial Monitor's Serial Writes

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related