/***********************************************************************        
 * Filename: Switches.c
 * This program demonstrates a way to simulate an analog read by measuring 
 * the time it takes to charge a capacitor through a resistance. It uses
 * resistors in series and buttons between them.
 ***********************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <wiringPi.h>

int ButtonPin = 0;   // Resistors in series and capacitor connected to pin zero.

/***********************************************************************        
 * RCtime() - Function, uses a digital pin to measure resistance by first 
 * discharging capacitor then measuring the time it takes to charge the
 * capacitor through the resistance. When the voltage rises to Vcc/2 the 
 * pin will go high.
 ***********************************************************************/
long RCtime(int RCpin)
{
  pinMode(RCpin, OUTPUT);             // Set pin to output,

  digitalWrite(RCpin, LOW);           // and pull to low.    

  delay(4);                           // Allow time to let capacitor discharge.

  long time = micros();
                          
  pinMode(RCpin, INPUT);              // Now set the pin to an input,
  pullUpDnControl(RCpin, PUD_OFF);    // turn off internal pull down resistor,
  while (digitalRead(RCpin) == LOW);  // and wait for it to go high.

  long PinVal = micros() - time;
  
  return PinVal;                                 
}

/**************************************************************************        
 * loop() - function runs in a continuous loop until program is stopped.
 **************************************************************************/
void loop(void)
{
  long ButtonReading = RCtime(ButtonPin); // Read Buttones into ButtonReading.

  switch(ButtonReading)
  {
    case 6200 ... 8000:
    {
      printf("%ld - No button pressed.\n", ButtonReading);
      break;
    }
    case 5500 ... 6199:
    {
      printf("%ld - button one pressed.\n", ButtonReading);
      break;
    }
    case 4500 ... 5499:
    {
      printf("%ld - button two pressed.\n", ButtonReading);
      break;
    }
    case 3000 ... 4499:
    {
      printf("%ld - button three pressed.\n", ButtonReading);
      break;
    }
    case 2000 ... 2999:
    {
      printf("%ld - button four pressed.\n", ButtonReading);
      break;
    }
    case 1000 ... 1999:
    {
      printf("%ld - button five pressed.\n", ButtonReading);
      break;
    }
  }
  delay(100);
}

/***********************************************************************        
 * setup() - function is run by main() one time when the program starts.
 ***********************************************************************/
void setup(void)
{
  wiringPiSetup();   // Required.

  RCtime(ButtonPin); // Throw out first reading.
}

/***********************************************************************        
 * main() - required
 ***********************************************************************/
int main(void)
{
  setup();

  while(1)
  {
    loop();
  }
}