Simple Communication: Raspberry -> Arduino

arduino.ino

 
int output = 9;//embedded led output, maybe is 13 

void setup() {                
  Serial.begin(9600);
  pinMode(output, OUTPUT);     
}

void loop() {
  if(Serial.available() > 0) {
    char command = toLowerCase(Serial.read());
    if(command == 'a') {
       digitalWrite(output,HIGH);  
    } else {
       digitalWrite(output,LOW); 
    } 
  }

}

raspberry.py

import serial
import time

arduino = serial.Serial('/dev/ttyAMA0')

while 1:
	arduino.write('a')
	time.sleep(1)
	arduino.write('b')
	time.sleep(1)