Dual Channel Telescope Dew Heater Controller

#include <16F88.h>
#device ADC=8  // return ADC values 0-255

#fuses INTRC,NOWDT,PUT,NOBROWNOUT,NOMCLR,NOLVP
#use delay(internal=8000000)  // 8MHz

#define POT1_PIN      PIN_A0  // POT 1
#define POT2_PIN      PIN_A1  // POT 2
#define BAT_VIN_PIN   PIN_A3  // Battery in to check voltage through voltage divider
#define POT_JUMPER    PIN_A7  // connect to +5v (with a 10K resistor) to use both pots or ground for one
#define PWM_PIN       PIN_B0  // LED for low battery
#define HEATER1_PIN   PIN_B1  // MOSFET 1
#define HEATER2_PIN   PIN_B2  // MOSFET 2

#define DELAY100         100  // 1/10th of a sec
#define DELAY_LEDBLINK   500  // 1/2 second

#define POTMIN             0  // minimum return value of the ADC when reading the POT
#define POTMAX           255  // maximum return value of the ADC when reading the POT


//  the voltage divider handles 0-18.5 volts, which should be overkill for any battery
//  This scales down to 0-5v for the pic to handle (using a 27K and 10K voltage divider)
//  11v is 84.6% of 13v (full battery) so 84.6% of 255 (ADC return max) is 215.
//  This will be calculated in the program so we can enter the voltage here.
//

#define VIN_MAX           16      // Max volts allowed (should be no more than about 13v from a car battery)
#define VIN_WARN        10.5      // low volts to start the LED warning
#define VIN_CUTOFF      10.1      // low volts to start the power cutoff
#define ADC_MAX          255
#define YELLOW_LED_OFF     0      // 0 (off)  - 255 (bright)
#define YELLOW_LED_ON     25      // 0 (off)  - 255 (bright)  Use 250 for a standard brightness LED, 25 for high brightness LED

#define ONEPOT             1  // how many pots are in use - depends on POT_JUMPER value
#define TWOPOTS            2

#define FULLPULSE         92   // longer number makes for a longer total peak to peak
                              // 93 is about 3 seconds. See below for a full explanation

//#define FULLPULSE         153  // longer number makes for a longer total peak to peak
                                // 153 is about 5 seconds. See below for a full explanation


//#pragma config CCPMX = RB0 // CCP1 Pin Selection bit (CCP1 function on RB0)
#use pwm(CCP1,TIMER=2,FREQUENCY=1000,DUTY=50)                              

//  Approximate FULLPULSE value for full pulse seconds.
//  Each second is about 30.6 (round up or down to whole number)
//  
//     SECONDS     FULLPULSE          SECONDS     FULLPULSE
//        1            31       |        6           184
//        2            61       |        7           214
//        3            92       |        8           245
//        4           122       |        9           275
//        5           153       |       10           306
//                               
// The interrupt (FULLPULSE) math is: 
//     The timer is incremented at (CLOCK/4)/RTCC_DIV. 
// The timer is incremented (8000000/4)/256 or 7812.5 times a second. 
// The interrupt happens every 256 increments. 
// With these numbers the interrupt happens 7812.5/256 or 30.517578125 times a second.
// Multiply that by our FULLPULSE for the actual full pulse time:
//    60/30.517578125 = once every 1.96608 us
//    1.96608 * 256 = 503 us seconds = 8.388608 seconds
//    1.96608 * 153 = 300 us seconds = 5 seconds
//    1.96608 * 62  = 121.9 us seconds = ~2 seconds


//                  PIC 16F88
//                -------------
//              -| A2       A1 |- 10k Pot #2 input
//  Battery VIN -| A3       A0 |- 10k Pot #1 input
//              -| A4       A7 |- Pot Count (+5v with 10k resistor=2, GND=1)
//        RESET -| A5/MCLR  A6 |- 
//          GND -| VSS     VDD |- +5v
// PWM Batt LED -| B0       B7 |- 
//     MOSFET 1 -| B1       B6 |- 
//     MOSFET 2 -| B2       B5 |- 
//              -| B3       B4 |- 
//                -------------
                

/*****************************************************************

  Dew Heater Controller code for a PIC 16F88
  By Allen Maroney   http://www.allenmaroney.com
  6/4/2015
  
  SPAC Optical Lab   http://www.telescopelab.com

                  PIC 16F88
                -------------
              -| A2       A1 |- 10k Pot #2 input
  Battery VIN -| A3       A0 |- 10k Pot #1 input
              -| A4       A7 |- Pot Count (+5v with 10k resistor=2, GND=1)
        RESET -| A5/MCLR  A6 |- 
          GND -| VSS     VDD |- +5v
PWM Batt LED -| B0       B7 |- 
    MOSFET 1 -| B1       B6 |- 
    MOSFET 2 -| B2       B5 |- 
              -| B3       B4 |- 
                -------------

*******************************************************************/

#include <Dew Heater Controller - Manual.h>

// need these to be global because they are set in main and used in the interrupt
int16 width1, width2;
int8 potreset;

// prototypes
void Read_Pot(int8 *pot1, int8 *pot2, int8 potcount);
int8 Read_BatteryVoltage(int8 adcwarnval, int8 adcoffval);


// *********************  must be before main()
#INT_RTCC 
void tick_interrupt(void) 
{ 
static int16 loop = 0, pulse1=0, pulse2=0;

if(loop++ > FULLPULSE || potreset)
  {
    loop = 0;
    potreset = 0;
    pulse1 = 0;
    pulse2 = 0;
  }

// this 'if' uses the pulse length of pot 1
// the >1 makes sure that the lowest setting turns the heater off
// at the highest setting there is a 1/250th of a pulse off blink to let you know that everything is working
if(pulse1 <= width1 && width1 > 1)
  { 
    output_high(HEATER1_PIN); 
    pulse1++; 
  } 
else 
  { 
    output_low(HEATER1_PIN); 
  } 

// this 'if' uses the pulse length of pot 2 (or the same as pulse 1 if only one pot is set up)
// the >1 makes sure that the lowest setting turns the heater off
// at the highest setting there is a 1/250th of a pulse off blink to let you know that everything is working
if(pulse2 <= width2 && width2 > 1)
  { 
    output_high(HEATER2_PIN); 
    pulse2++; 
  } 
else 
  { 
    output_low(HEATER2_PIN); 
  } 

}


void main()
{
  int8 pot1=0, pot2=0, oldpot1=0, oldpot2=0, potcount=ONEPOT;
  int8 adcwarnval=0, adcoffval=0, poweron=1;
  
  width1=0;  // set the default of the globals
  width2=0;
  potreset=0;
  
  set_tris_a(0b10001011);  // A0-A1, A3, A7 inputs; A2, A4-A5 output
  set_tris_b(0b00000000);  // B0-B7 all output
  
  output_low(HEATER1_PIN); 
  output_low(HEATER2_PIN); 
  delay_ms(DELAY100);  // let the internal R/C clock charge up and stabilize
  
  //   setup ADC ports for the pots on A0 and A1   
  //   The Jumper connects to A2
  //   The voltage divider feeds A3
  setup_adc_ports(sAN0|sAN1|sAN3|VSS_VDD);
  setup_adc(ADC_CLOCK_INTERNAL);

  /// see if we are using one pot or two
  if(input(POT_JUMPER) )  // POT_JUMPER connected to 5v use two pots
      {    // blink each LED back and forth a few time if we are using two pots
      potcount = TWOPOTS;
      output_high(HEATER1_PIN);
      output_low(HEATER2_PIN);
      delay_ms(DELAY_LEDBLINK);
      output_low(HEATER1_PIN);
      output_high(HEATER2_PIN);
      delay_ms(DELAY_LEDBLINK);
      output_high(HEATER1_PIN);
      output_low(HEATER2_PIN);
      }
  else  // POT_JUMPER connect to GROUND (default)
      {  // blink both LEDs on for a second at the same time if we use one pot
      potcount=ONEPOT;
      output_high(HEATER1_PIN); 
      output_high(HEATER2_PIN); 
      delay_ms(DELAY_LEDBLINK); 
      }
  delay_ms(DELAY_LEDBLINK); 
  output_low(HEATER1_PIN);  // turn off the LEDS 
  output_low(HEATER2_PIN); 
  delay_ms(DELAY_LEDBLINK); 


  // calculate the minimum threshold for the low battery LED to start lighting up
  // we only need to calculate these once
  adcwarnval = (int8)((double)(ADC_MAX-1) * ((double)VIN_WARN/(double)VIN_MAX));
  adcoffval  = (int8)((double)(ADC_MAX-1) * ((double)VIN_CUTOFF/(double)VIN_MAX));
  
  //// Setup CCP to PWM Mode
  setup_ccp1(CCP_PWM);
  setup_timer_2((Long int)T2_DIV_BY_16,255,1);
  set_pwm1_duty(YELLOW_LED_ON); 
  
  // set up the interrupt
  set_rtcc(0); 
  setup_counters(RTCC_INTERNAL, RTCC_DIV_256);
  enable_interrupts(INT_RTCC); 
  enable_interrupts(GLOBAL); 

  while(true)
  {
  poweron = Read_BatteryVoltage(adcwarnval, adcoffval);

  if( poweron )  // as long as the battery is > VIN_CUTOFF
      {
      Read_Pot(&pot1, &pot2, potcount);

      // stop jittering
    if(oldpot1 < pot1-1 || oldpot1 > pot1+1 ||
        oldpot2 < pot2-1 || oldpot2 > pot2+1 )
        {
        width1 = (int16)((float)FULLPULSE * ((float)pot1/(float)POTMAX)); // pot1 values 0-255
        width2 = (int16)((float)FULLPULSE * ((float)pot2/(float)POTMAX)); // pot2 values 0-255
        oldpot1 = pot1;
        oldpot2 = pot2;
        potreset = 1;
        }
      }
    else   // low battery turns off the mosfets
      {
      width1=0;   // turn off power to mosfet 1
      width2=0;   // turn off power to mosfet 2
      if( pot1 > 2) // forces going into the pot if() should the power go back up
            { oldpot1 = pot1-2; }  
      else  { oldpot1 = pot1+2; }
      }

    delay_ms(DELAY100);    // 1/10th sec
  }

}


// ********************* START READ POT

void Read_Pot(int8 *pot1, int8 *pot2, int8 potcount) 
{
  ////////////////  READ 10K POTS ////////////////// 
  Set_adc_channel(0);  // Select Analog port connected to pot1 (A0)
  delay_us(20); 
  *pot1 = read_adc(); // Read value 
    if( *pot1 < POTMIN+1 )
        { *pot1 = POTMIN+1; }
    if( *pot1 > POTMAX-1 )
        { *pot1 = POTMAX-1; }

  if( potcount == TWOPOTS )
  {
      Set_adc_channel(1); // Select Analog port connected to pot2 (A1)
      delay_us(20); 
      *pot2 = read_adc(); // Read value 
      if( *pot2 < POTMIN+1 )
          { *pot2 = POTMIN+1; }
      if( *pot2 > POTMAX-1 )
          { *pot2 = POTMAX-1; }
  }
  else
  {
      // pot #2 not used so return pot 1's value
      *pot2 = *pot1;
  }
}

// ********************* START READ_BATTERYVOLTAGE

int8 Read_BatteryVoltage(int8 adcwarnval, int8 adcoffval)
{
  static int8 vin=ADC_MAX;  // start with no warnings
  static int8 ledon=YELLOW_LED_ON, ledctr=0, lowvoltjitterwarn=0, lowvoltjittercutoff=0;
  
  ////////////////  BATTERY VOLTAGE IN ////////////////// 
  Set_adc_channel(3);  // Select Analog port connected to A3
  delay_us(20); 
  
  if(!input_state(HEATER1_PIN) && !input_state(HEATER2_PIN)) // only update voltage when the heaters are off
      {
      vin = read_adc(); // Read value 
      }
  
  // once the voltage drops to the warn or cutoff level
  // this raises the value (if>0)  to get back to the higher
  // state to reduce blinking between states.
  adcwarnval += lowvoltjitterwarn;
  adcoffval += lowvoltjittercutoff;

  if( vin > adcwarnval )
      {  // all is well, > 11V
      lowvoltjitterwarn=0;  // back to normal for warn
      lowvoltjittercutoff=0;  // back to normal for cutoff
      set_pwm1_duty(YELLOW_LED_OFF);
      return(1);  // power on to the heaters
      }
  else if( vin > adcoffval )
      {  // low power warning > 10v <= 11v turn yellow LED on solid
      lowvoltjitterwarn=1;
      lowvoltjittercutoff=0;  // back to normal for cutoff
      set_pwm1_duty(YELLOW_LED_ON);
      return(1);  // power on to the heaters
      }
  else     // <= 10v
      { // cut off power, blink yellow led
      lowvoltjittercutoff=1;
      if(ledctr++ > 5 )    // 5 = 1/2 sec blinks (10 = 1 sec blinks)
        {
        if(ledon == YELLOW_LED_ON)  // if yellow led currently on then turn it off
              { ledon=YELLOW_LED_OFF; }
        else  { ledon=YELLOW_LED_ON; }
        set_pwm1_duty(ledon);
        ledctr=0;
        }
      return(0);  // power OFF to the heaters
      }
}