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I am working on object tracking robot. I am using python and OpenCV to detect the object and send the proper data to the arduino that controls two servo motors. The data which should be sent to the arduino are servo motors angles ranging between 0-180. I am using sample codes to understand how python and arduino communicate using serial bus.When I send a single digit, the arduino receives it and work as intended, but when I send more than one digit nothing happens. This is the arduino code:

#include <Servo.h>
int data;
Servo myservo;  // create servo object to control a servo
// twelve servo objects can be created on most boards
int pos = 0;    // variable to store the servo position

void setup() { 
  Serial.begin(9600); //initialize serial COM at 9600 baudrate
  pinMode(LED_BUILTIN, OUTPUT); //make the LED pin (13) as output
  digitalWrite (LED_BUILTIN, LOW);
  myservo.attach(9);
  Serial.println("Hi!, I am Arduino");
}

void loop() {
while (Serial.available()){
 //to receive more than one character 
 char buffer[] = {' ',' ',' ',' ',' ',' ',' '}; // Receive up to 7 bytes
 while (!Serial.available()); // Wait for characters
 Serial.readBytesUntil('n', buffer, 7);
 data = atoi(buffer);

}
myservo.write(data);
}

And here is the python code:

import serial
import time  # Required to use delay functions

arduinoSerialData = serial.Serial('com14', 9600)  # Create Serial port 
object called arduinoSerialData
time.sleep(2)  # wait for 2 secounds for the communication to get 
established

print arduinoSerialData.readline()  # read the serial data and print it as 
line
print ("Enter 1 to turn ON LED and 0 to turn OFF LED")

while 1:  # Do this forever

    var = raw_input()  # get input from user
    print "you entered", var  # print the intput for confirmation

    arduinoSerialData.write(var)
  • the only debugging code that you have is Serial.println("Hi!, I am Arduino"); .... put in more debugging code to determine what is being received – jsotola Sep 8 '18 at 18:11
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If the python Serial write function sends byte, then you should read it in Arduino with Serial.read().

void loop() {
  if (Serial.available()){
    byte data = Serial.read();
    myservo.write(data);
  }
}

If python sends the number as text, then you can read it with parseInt().

void loop() {
  if (Serial.available()){
    int data = Serial.parseInt();
    myservo.write(data);
  }
}

The parseInt is one of the blocking functions and will by default wait one second for next char after the last sent digit was received. But the number is sent at once from python so the delays between digits are small. Set in setup() Serial.setTimeout(10);

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