voodoo_bunny.c

#include <FreqCounter.h>

/** Constants **/
const int NUMBER_OF_CALIBRATION_CYCLES = 10; // Number of 250ms calibrations to determine the baseline sensor value
const int FUDGE_FACTOR = 1.5; // Deviation from baseline that triggers switch
const int TIMEOUT = 2000; // Number of loop cycles to deactivate fan between presses
enum STATE { ACTIVATED, DEACTIVATED };

/** Pins **/
const int relayPin = 12;
const int ledPin = 13; // activates when switch is triggered

/** Variables **/
unsigned long baseline;
int timeSincePress;
STATE state;

void setup() {
  pinMode(relayPin, OUTPUT);
  pinMode(ledPin, OUTPUT);
  
  // Initialize the frequency counter on pin 5
  // Read from counter every 250ms to see how many pulses there are from the fan
  FreqCounter::start(250);
  
  baseline = getSensorBaseline();
}

void loop() {
  unsigned long currentValue = getSensorValue();
  
  if(currentValue < (baseline * FUDGE_FACTOR)) {
    
    activateSwitch();
    
  } else if(state == ACTIVATED) {
    
    if(timeoutExpired()) {
      
       deactivateSwitch();
       
    } else {
      
        tickTimeout();
        
    }
    
  }
  
}

unsigned long getSensorValue() {
  unsigned long frequency;
  
  // Idle until the 250ms have elapsed
  while (FreqCounter::f_ready == 0) 
  
  // Grab most recent frequency value
  frequency = FreqCounter::f_freq;
  
  return frequency;
}

unsigned long getSensorBaseline() {
  unsigned long average;
  
  // Poll the sensor NUMBER_OF_CALIBRATION_CYCLES times, find the average
  for(int i=0; i < NUMBER_OF_CALIBRATION_CYCLES; i++)
    average += getSensorValue();
  average /= NUMBER_OF_CALIBRATION_CYCLES;
  
  return average;
}

void activateSwitch() {
  digitalWrite(relayPin, HIGH);
  digitalWrite(ledPin, HIGH);
  
  state = ACTIVATED;
  timeSincePress = 0;
}

void deactivateSwitch() {
  digitalWrite(relayPin, LOW);
  digitalWrite(ledPin, LOW);
  
  state = DEACTIVATED;
}

boolean timeoutExpired() {
  timeSincePress > TIMEOUT;
}

void tickTimeout() {
  timeSincePress++;
}