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I'm trying to send 3 ints in the range of 0-180 from Python to the Arduino Uno device using pySerial (py3K). I have managed to send 1 int by using python's struct lib (not sure if it's the best or fastest way but it works). However I'm failing to send more than 1 and every example online seems to stop at 1.

Here's the simplified code. The task is to send servo0-servo4 to the arduino and apply those values to the corresponding servos.

Python Code

import serial
import struct
import time

bge.arduino = serial.Serial('/dev/ttyACM0', 9600)

# let it initialize
time.sleep(2)

# send the first int in binary format
bge.arduino.write(struct.pack('>B', 45))

Arduino code

#include <Servo.h>
Servo servo0;
Servo servo1;
Servo servo2;

void setup(){
  Serial.begin(9600);
  servo0.attach(3);
  servo1.attach(5);
  servo2.attach(6);
}

void loop(){
  if(Serial.available()){
    int message = Serial.read();
    // control the servo
    servo0.write(message);
  }
}
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2 Answers 2

up vote 0 down vote accepted

I guess I'll answer my own question for anyone else having this issue. What I did was:

Python:

# write to arduino as raw binary
bge.arduino.write(struct.pack('>BBB',45,90,180))

Arduino:

#include <Servo.h>

Servo servo0;
Servo servo1;
Servo servo2;

// create array
int incoming[2];

void setup(){
  Serial.begin(9600);

  servo0.attach(3);
  servo1.attach(5);
  servo2.attach(6);
}

void loop(){
  while(Serial.available() >= 3){
    // fill array
    for (int i = 0; i < 3; i++){
      incoming[i] = Serial.read();
    }
    // use the values
    servo0.write(incoming[0]);
    servo1.write(incoming[1]);
    servo2.write(incoming[2]);
  }
}
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You're not verifying if Serial.available() has 3 values available. So it's going to get filled with -1's if there aren't. Check to see how many bytes are in the receive buffer. –  baldengineer Mar 27 at 23:28
up vote 0 down vote 
void loop(){
  if(Serial.available() >= 3){
    // fill array
    for (int i = 0; i < 3; i++){
      incoming[i] = Serial.read();
    }
    // use the values
    servo0.write(incoming[0]);
    servo1.write(incoming[1]);
    servo2.write(incoming[2]);
  }
}
share|improve this answer
    
Thank you @baldengineer. I'm now verifying like you proposed. However after a little while of playing with the program it completely messes up and I have to reboot the Arduino for it to work again. I suspect the ordering of the bytes might be shuffling? –  ZanQdo Mar 29 at 0:15
    
Holly cow, I think I solved the problem by replacing if(Serial.available().. with while(Serial.available().. Does that make sense to you? –  ZanQdo Mar 30 at 3:21

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