Question

I want to send some data to an Arduino through pyserial in Python. All I want to the Arduino to do is read the variable length string data from the serial port, and write it back so that Python can read it. Since I’ve been unable to do that, the code below only has Python sending on character. Here’s the Python code:

import serial
import sys
import pywapi
import time

def main():
    ser = serial.Serial(3, 9600, timeout=1)
    print "Conn established"
    print "Sending: %s" % "z".__repr__()
    print ser.write('z'.encode("ascii"))
    time.sleep(2)
    print "Received: %s" % ser.read(10).__repr__()         
    ser.close()

Here’s the Arduino code:

void setup(){
  analogReference(DEFAULT);
  Serial.begin(9600);
}

void loop(){
  if(Serial.available() > 0)
    Serial.println("x");
  while(Serial.available() > 0){
    Serial.print(Serial.read(), BYTE);
  }
}

The output:

Conn established
Sending: 'z'
1
Received: ''

I know the code for the Arduino works because it works when data is being sent from the Arduino terminal. However, the moment I try to send anything from Python it fails. I’ve been struggling with this all day. Any help would be greatly appreciated.

Answer 1

Try increasing or removing the timeout, and set read’s size to 1. You may also want to increase the sleep delay, or even implement a simple read loop.

Something like:

try:
    while True:
        data = ser.read(1).__repr__()
        if data:
            print "Received: %s." % data
        else:
            print "Looping."
except KeyboardInterrupt:
    print "Done."
except:
    raise
finally:
    ser.close()
    print "Closed port."

Then just use ctrl-c to stop it.