// Dec 30 2014
// The purpose of this sketch is to intercept the signal pin on the Transmitter to allow for remote switcing of
// equipment.  ie. trigger a lost model piezo buzzer, bomb drop, squirt gun etc on the Quad. This code reads the PWM signal length.
// Requires the Signal wire + GND from the Receiver unit.  Must ensure Arduino and RC grounds are tied. 
// The signal tester here for "GEAR" is ~104x when LOW and ~1867 when HIGH
// Use this to switch an external power signal via a MOSFET or other control.

// The below example is specific to triggering a buzzer when the TX signal goes above 1400. However, you can make this whatever you like. In my case,
// channel 5 is triggere HIGH when the Aux switch is enabled. This turns the alarm on.  The idea is that I use the remote to trigger the alarm to turn
// on (as opposed to having the alarm trigger ON when the TX is turned off, or out of range).  If you are looking for that functionality, y
// this is a starting place, but you will have to determine what signal comes from your RX when the transmitter powers off.

// Note - The LED is optional, but could help locating your model in the dark.

// Note - if you are going to use an AtTiny, you will need to use Arduino-Tiny (https://code.google.com/p/arduino-tiny/) as the
// default bootloader does not support Tone().   Instructions are on the link.

//Uno - use for initial testing as programming/testing a Tiny is a PINTA.
//int rcPin = 10;    // PWM signal arduino pin
//int buzzerPin = 4; //buzzer pin

//ATTiny85  - pinouts are here http://highlowtech.org/wp-content/uploads/2011/10/ATtiny45-85.png
//pin #1 has the black dot on the chip.
// 1      8
// 2      7
// 3      6
// 4      5


int rcPin = 0;     // PWM signal in from RC receiver - connect to Pin 5 (see above)
int buzzerPin = 1;  //Buzzer pin out to buzzer  - connect to Pin 6 (see above)
int ledPin = 2;     //Optional - connect to Pin 6 (see above)
int chPWMVal = 0;        // Receiver channel pwm value - connect to a free channel on your RX. Leave value at 0.

void setup() {
  pinMode(rcPin, INPUT);
  pinMode(buzzerPin, OUTPUT);  
  pinMode(ledPin, OUTPUT);    
  //Serial.begin(9600);  //for debugging
}

void loop() {
  // Read in the length of the signal in microseconds
  chPWMVal = pulseIn(rcPin, HIGH, 25000);
  digitalWrite(ledPin, LOW);   // turn the LED on (HIGH is the voltage level)
  //Serial.print("Channel #: ");
  //Serial.println(ch);
  if (chPWMVal > 1400)
  {
    digitalWrite(ledPin, HIGH);   // turn the LED on (HIGH is the voltage level)
    tone(buzzerPin, 3000, 300);
    delay(800);
    digitalWrite(ledPin, LOW);    // turn the LED off by making the voltage LOW
    delay(200);
  }
}