uint16_t readVcc(void) {
  uint16_t result;
  // Read 1.1V reference against Vcc
  ADMUX = (0<<REFS0) | (12<<MUX0);
  delay(2); // Wait for Vref to settle
  ADCSRA |= (1<<ADSC); // Convert
  while (bit_is_set(ADCSRA,ADSC));
  result = ADCW;
  return 1018500L / result; // Back-calculate AVcc in mV
}

// http://blog.onlinux.fr/
//
//
//                           +-\/-+
//          Ain0 (D 5) PB5  1|    |8  Vcc
//          Ain3 (D 3) PB3  2|    |7  PB2 (D 2) Ain1 -
// LED +pin Ain2 (D 4) PB4  3|    |6  PB1 (D 1) pwm1 - Shock sensor pin
//                     GND  4|    |5  PB0 (D 0) pwm0 - RF433 tx pin
// 
// **** INCLUDES *****
#include <avr/sleep.h>
#include <avr/wdt.h>
#include <RCSwitch.h>
 
#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif
 
#define LOW_BATTERY_LEVEL 2500 //mV. Led will flash if battery level is lower than this value
#define WDT_COUNT  225  // wdt is set to 8s, 8x225=1800 seconds = 30 minutes
 
volatile boolean f_wdt = 0;
volatile byte count = WDT_COUNT;
volatile boolean f_int = 0;
volatile boolean lowBattery = 0;
volatile boolean switchState = HIGH;
 
const byte TX_PIN   = PB0;  // Pin number for the 433mhz OOK transmitter
const byte LED_PIN  = PB4;
const byte WAKEUP_PIN = PB1;  // Use pin 1 as wake up pin
 
RCSwitch mySwitch = RCSwitch();
 
/******************************************************************/
 
void setup()
{
  setup_watchdog(9);
  pinMode(TX_PIN, OUTPUT);
  pinMode(WAKEUP_PIN, INPUT);        // Set the pin to input
  digitalWrite(WAKEUP_PIN, HIGH);    // Activate internal pullup resistor  
  mySwitch.enableTransmit(TX_PIN);
 
  mySwitch.switchOn('e', 3,2);      // Test Zibase signal id E10
 
  lowBattery =  !(readVcc() >= LOW_BATTERY_LEVEL); // Initialize battery level value
 
  PCMSK  |= bit (PCINT1);  // set pin change interrupt PB1
  GIFR   |= bit (PCIF);    // clear any outstanding interrupts
  GIMSK  |= bit (PCIE);    // enable pin change interrupts  
  sei();         
}
 
 
// set system into the sleep state 
// system wakes up when watchdog is timed out
void system_sleep() {
  cbi(ADCSRA,ADEN);                    // switch Analog to Digitalconverter OFF
 
  set_sleep_mode(SLEEP_MODE_PWR_DOWN); // sleep mode is set here
  sleep_enable();
 
  sleep_mode();                        // System sleeps here
 
  sleep_disable();                     // System continues execution here when watchdog timed out 
  sbi(ADCSRA,ADEN);                    // switch Analog to Digitalconverter ON
}
 
// 0=16ms, 1=32ms,2=64ms,3=128ms,4=250ms,5=500ms
// 6=1 sec,7=2 sec, 8=4 sec, 9=8sec
void setup_watchdog(int ii) {
 
  byte bb;
  int ww;
  if (ii > 9 ) ii=9;
  bb=ii & 7;
  if (ii > 7) bb|= (1<<5);
  bb|= (1<<WDCE);
  ww=bb;
 
  MCUSR &= ~(1<<WDRF);
  // start timed sequence
  WDTCR |= (1<<WDCE) | (1<<WDE);   
  // set new watchdog timeout value   
  WDTCR = bb;   WDTCR |= _BV(WDIE); 
}
 
// Watchdog Interrupt Service / is executed when watchdog timed out 
ISR(WDT_vect) {   
  if (count >= WDT_COUNT) {
   f_wdt=true;  // set WDTl flag
   count=0;
  }
  count++;
} 
 
ISR (PCINT0_vect){
  f_int=true; // set INT flag
}
 
void loop()
{
  system_sleep();
 
  if (lowBattery)        // lowBattery is at setup().
    lowBatteryWarning(); // Flash for 1ms every 8s http://www.gammon.com.au/power
 
 
  if (f_int) {
    blink(2);
    cli();
    mySwitch.switchOn('e', 3,2);      // Zibase signal id E10
    f_int=false;  // Reset INT Flag
    sei();
  } 
  else if ( f_wdt ) {
    blink(5);
    cli(); // disable interrupts
    lowBattery = !(readVcc() >= LOW_BATTERY_LEVEL);
    f_wdt=false; // reset WDT Flag
    sei(); // enable interrupts
  }
 
}
 
 
void blink(int ii) {
  pinMode(LED_PIN, OUTPUT);
  for (byte i = ii ;  i > 0 ; i--){
     digitalWrite(LED_PIN, HIGH);
     delay(50);
     digitalWrite(LED_PIN, LOW); 
     delay(50);
  }
 
  pinMode(LED_PIN, INPUT); // reduce power
}
 
void lowBatteryWarning () {
  pinMode(LED_PIN, OUTPUT);
  digitalWrite (LED_PIN, HIGH);  
  delay (1);       // mS        
  digitalWrite (LED_PIN, LOW);    
  //delay (999); 
  pinMode(LED_PIN, INPUT); // reduce power  
}
 
uint16_t readVcc(void) {
  uint16_t result;
  // Read 1.1V reference against Vcc
  ADMUX = (0<<REFS0) | (12<<MUX0);
  delay(2); // Wait for Vref to settle
  ADCSRA |= (1<<ADSC); // Convert
  while (bit_is_set(ADCSRA,ADSC));
  result = ADCW;
  return 1018500L / result; // Back-calculate AVcc in mV
}