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I am using Arduino and Python 3.4 with pySerial and am trying to send multiple bytes through serial communication, but am having issues since my code is running, but the print statements I have in certain places for debugging purposes are outputting strings which I am not expecting. I have tried writing a simplified version of this code and it works correctly, so I am not sure what I am doing wrong! Also, in an attempt to fix this, I put in an if statement in which has slowed down the code a lot. Any suggestions on how to streamline the code to be faster and/or how to send and receive the right data would be much appreciated!

Python: 

#sources:
#http://stackoverflow.com/questions/676172/full-examples-of-using-pyserial-package for more info
#http://pyserial.sourceforge.net/pyserial_api.html

import serial 
import time

#sets the connection parameters, relook at when know more
ser = serial.Serial(
    port ='COM4', 
    baudrate = 9600, 
    parity = serial.PARITY_ODD, 
    stopbits = serial.STOPBITS_TWO, 
    bytesize = serial.EIGHTBITS,
    timeout = 5
    )

def decToPercent (decimal):
    #maps value from 0-1 to 0-255 and makes into an interger, then to hex
    intPercent = round(decimal*255)
    return intPercent

ser.isOpen()    #returns true?

firstContact = False 
inByte = 0
wrist = 0.9         #setup of variables which I will get from dictionary of other code once integrate
elbow = 0       #assuming variables will be included in (0-1)   

wristPerc = decToPercent(wrist)
elbowPerc = decToPercent(elbow)

forceBytes = bytearray([wristPerc, elbowPerc])      #puts the motor values into an array as hex
print(forceBytes)

#set up initial contact with the arduino 
inByte = ser.read(1)
print(inByte)

while True:
    if (firstContact == False):

        if inByte == b'A' :
            firstContact = True
            ser.write('a'.encode())
            inByte = ser.read(1)

    else:

        ser.write(forceBytes)
        time.sleep(0.05)
        print(ser.readline())

Initially I had the code start and go back through the whole while statement after using this code, however I took it out because I think it was making the flow of code mess up the outputs a little:

    #starts the process over again, clears so that have time to get information
    firstContact = False        
    inByte = ser.read(1)
    print(inByte)

Arduino code:

//See Arduino Cookbook chapter 4 for info on sending and recieving multiple messages in one
//See example of serial call response for strategy on how to process information faster
int motorPinLeft = 10;
int motorPinRight = 11; 
int motorSpeedLeft = 0;
int motorSpeedRight = 0;

int fieldIndex = 1;
char values[2];    //array holding values for the fields we expect 
char newByte = 0;

void setup() {
  pinMode(motorPinLeft, OUTPUT);
  pinMode(motorPinRight, OUTPUT);
  Serial.begin(9600);
  while(!Serial){}; //waits for arduino to be ready, not neaded for duo
  establishContact();
}

void loop() 
{
  while (Serial.available()>0)    //checks to see if anything needs to be sent,
  {                            //denoted by recieveing signal from pySerial
      char inByte = Serial.read();

      switch (inByte)
      {
        case 97:
          inByte = 0;
          break;

        default:

          values[0] = inByte;
          //could just call Serial.read and asign 2nd byte, but loop allows to send more variables later
          if (fieldIndex < 2)
          {
            newByte = Serial.read();
            values[fieldIndex] = newByte;
            fieldIndex++;
          }

          else
          {
            Serial.print(values[0], DEC);    //debugging purposes 
            Serial.print(values[1], DEC);

            motorSpeedLeft = values[0];
            motorSpeedRight = values[1];

            //Serial.print(motorSpeedLeft);
            //Serial.print(motorSpeedRight);

            analogWrite(motorPinLeft, motorSpeedLeft);
            analogWrite(motorPinRight, motorSpeedRight);


            delay(3000);     //  to make the motor vibrate for 1 second

            motorSpeedRight = 0;
            motorSpeedLeft = 0;

            analogWrite(motorPinLeft, motorSpeedLeft);
            analogWrite(motorPinRight, motorSpeedRight);

            delay(1000);
          }
      }

      //Serial.print('A');


  }
}


//allows arduino to be ready before pySerial sends any messages
void establishContact()
{
  while (Serial.available()<=0) 
  {
    Serial.print('A');
    delay(300);
  }
}

Output:

bytearray('b\xb2\x00')
b'A'
b'0K\xfe'
b'-\x13j10k\xfe'
b'-\x13j10k\xfe'

My motor is running each time a print statement occurs, so I am not sure if it is just my print statements that are messing up, rather than the actual serial communication?

One additional thing I am unsure of, is in my switch-case statement in the arduino code, I am using the ascii code for 'a' (97) instead of actually putting 'a'. Should both work?

rtmurad
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1 Answers1

0

After more messing around, I got the code to print out the right outputs by switching from Serial.print() to Serial.write() in the arduino code, and since I'm pretty sure that was the major issue, I went back to my original code, without an if statement which cut down the time it took to run the code. I did have a little trouble printing out both outputs, but by putting:

delay(10)

in between the Serial.write statements, it fixed that.

rtmurad
  • 127
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