Serial communication between arduino and raspberry pi works once, then stops working

Question

I'm using a Arduino Uno Rev 3 connected over usb to a Raspberry Pi Modell B+ running Rasbian.

Here ist the arduino code:

int input = 0;
String command = ""; // beinhaltet den aktuellen befehl
int Action = 1;
void setup() {
Serial.begin (9600);
}
void loop() {
 if (Serial.available() > 0) 
 {
 input = Serial.read();
 char currentChar = input;
 if(currentChar == '!') // frage nach trennzeichen
 {
 Serial.println(command);
 //Serial.write(Action);
 Action = command.toInt();
 command = ""; // befehl wieder leeren
 }else
 {
 command = command + currentChar ; // falls noch kein trennzeichen vorhanden, erweitere kommando
 }
 }
}

Here is the Raspberry Pi code (in python)

import serial
from time import sleep as sleep
ser = serial.Serial('/dev/ttyACM0',9600)
s = [0]
while True:
 ser.write(b'2!')
 a = ser.read(1)
 print a
sleep(2)

It always works if once after the code was uploaded to the arduino, but if I stop the script on the pi and restart it it stops working. What is the problem here?

• Code Gorilla: Does the PI close the serial port as it exits? If it doesn't can it open it again?
• Edgar Bonet: It works on my PC running Ubuntu, although it prints tons of CR and LF. You may have noticed that you are overflowing the Arduino's input buffer.
• jonathan: @EdgarBonet how do I prevent the input buffer from overflowing?
• Edgar Bonet: Speak slowly, e.g. by moving the sleep(2) inside the loop. You may also want to read the whole answer (3 bytes) in each iteration.
• Gerben: You do know that the Uno resets, when you create a new serial connection to it, right?

Answer 1

"It always works if once after the code was uploaded to the arduino...." Whenever you you reset the arduino the link between the arduino and the rasperry pi is broken momentarily thus causing the code on the raspberry pi to hang/ffreeze and not responding/ showing any valid results.

Try giving a keyboard interrupt by ( Ctrl + Z ) and restart the python script and that should work just fine!