/*  Frequency Counter With LCD Display - by arduinoaleman - May 2015
    updated by alexP December 2018
    Pin D5 of Arduino must be used for frequency input.
    Counter1 : 16 bits / used to count the frequency impules
    Counter2 : 8 bits / used to generate a 1000ms or 100ms gate time for measurement
    I use "bitClear(TIMSK0,TOIEO)" instead of "TIMSK0 &=~(1<<TOIE0)"
    I use "bitSet(TIMSK0,TOIEO)"   instead of "TIMSK0 |=~(1<<TOIE0)"
*/

#include <avr/interrupt.h>
#include <LiquidCrystal.h>
LiquidCrystal lcd(13,11,6,4,3,2);
volatile unsigned long frequency=0;            
volatile boolean       measurement_ready;
volatile unsigned char overflow_counter;     // number of overflows within gate_time
volatile unsigned int  time_so_far;              // number of ISR calls
volatile unsigned int  gate_time;                 

void measurement(int ms) {

    bitClear(TIMSK0,TOIE0);     // disable counter0 in order to disable millis() and delay()
                                // this will prevent extra interrupts that disturb the measurement
    delayMicroseconds(66);      // wait for other interrupts to finish
    gate_time=ms;               // usually 1000 (ms)
  
    // setup of counter 1 which will be used for counting the signal impulses

    TCCR1A=0;                   // reset timer/counter1 control register A
    TCCR1B=0;                   // reset timer/counter1 control register B
    TCCR2A=0;                   // reset timer/counter1 control register A
    TCCR2B=0;                   // reset timer/counter2 control register A
    
    // setup of counter2 which will be used to create an interrupt every millisecond (used for gate time)

    TCCR2B |= B00000101;        // set prescale factor of counter2 to 128 (16MHz/128 = 125000Hz)
                                // by setting CS22=1, CS21=0, CS20=1

    bitSet(TCCR2A,WGM21) ;      // set counter2 to CTC mode
                                // WGM22=0, WGM21=1, WGM20=0                   
    OCR2A = 124;                // CTC divider will divide 125Kz by 125 
   
    measurement_ready=0;        // reset
    time_so_far=0;              // reset
    bitSet(GTCCR,PSRASY);       // reset the prescaler 
    TCNT1=0;                    // set frequency counter1 to 0
    TCNT2=0;                    // set gate time counter2 to 0
      
    bitSet(TIMSK2,OCIE2A);      // enable counter2 interrupts
    TCCR1B |= B00000111;        // set CS12, CS11 and CS10 to "1" which starts counting 
                                // on T1 pin (Arduino pin D5)
 }


ISR(TIMER2_COMPA_vect) {
 
  if (time_so_far >= gate_time) {         // end of gate time, measurement is ready
    TCCR1B &= B11111000;                  // stop counter1 by setting CS12, CS11 and CS10 to "0"
    bitClear(TIMSK2,OCIE2A);              // disable counter2 interrupts
    bitSet(TIMSK0,TOIE0);                 // enable Timer0 again // millis and delay
    measurement_ready=true;               // set global flag for end count period
                                          // calculate now frequeny value 
    frequency=0x10000 * overflow_counter; // mult #overflows by 65636 (0x10000)
    frequency += TCNT1;                   // add counter1 contents for final value
    overflow_counter=0;                   // reset overflow counter
  }
  else {
    time_so_far++;                        // count number of interrupt events
    if bitRead(TIFR1,TOV1)  {             // if Timer/Counter 1 overflow flag = "1" then ...
       overflow_counter++;                // increase number of counter1 overflows
       bitSet(TIFR1,TOV1);                // reset counter1 overflow flag
    }
  };
}


void setup() {

  pinMode(A4, INPUT_PULLUP);
  pinMode(5,INPUT);
  lcd.begin(16, 2);                            // defines a LCD with 16 columns and 2 rows
  lcd.clear();
  
  for (int row=0; row<=1; row++) {
    for (int column=0; column<=16; column++) { // LDC test
       lcd.setCursor(column,row);
       lcd.print("*");
       delay(20);
    };
  }
  lcd.clear();
  }


void loop() {
  float floatfrq;  
  int range;
  long frq;

if(digitalRead(A4)== LOW)
{softReset();}

  measurement(1000);                     // 1000ms standard gate time
     
  while (measurement_ready==false);
  frq=frequency;

  floatfrq=frq;                          // type conversion (required!!)
  
  if ((frq >= 0)&& (frq < 10))           {range=0;};                           // Hertz
  if ((frq >= 10)&& (frq < 100))         {range=1;};   
  if ((frq >= 100)&& (frq < 1000))       {range=2;};
  if ((frq >= 1000)&& (frq < 10000))     {range=3; floatfrq=floatfrq/1000;};   // KHz
  if ((frq >= 10000)&& (frq < 100000))   {range=4; floatfrq=floatfrq/1000;};
  if ((frq >= 100000)&& (frq < 1000000)) {range=5; floatfrq=floatfrq/1000;};
  if (frq >= 1000000)                    {range=6; floatfrq=floatfrq/1000000;};// MHz 
  
  lcd.setCursor(0, 0);                 
  lcd.print("Freq:           ");        
   
  switch(range) {             
    case 0:                                          
       if (frq!=0) 
       {lcd.setCursor(6, 0);lcd.print(frq);
       lcd.setCursor(13,0);lcd.print("Hz ");}
       else
       {lcd.clear();lcd.setCursor(0, 0);
       lcd.print("No signal...   ");}
       
       
       break;
    case 1:   // 10Hz thru 100Hz
       lcd.setCursor(6, 0);   lcd.print(frq);
       lcd.setCursor(13,0);   lcd.print("Hz ");    
       break;
    case 2:    // 100Hz thru 1KHz
       lcd.setCursor(6, 0);   lcd.print(frq);
       lcd.setCursor(13,0);   lcd.print("Hz ");    
       break;
    case 3:    // 1KHz thru 10KHz
       lcd.setCursor(6, 0);   lcd.print(floatfrq,3);
       lcd.setCursor(13,0);   lcd.print("kHz");    
       break;
    case 4:   // 10KHz thru 100KHz
       lcd.setCursor(6, 0);   lcd.print(floatfrq,2);
       lcd.setCursor(13,0);   lcd.print("kHz");    
       break;
      case 5:   // 100KHz thru 1MHz
       lcd.setCursor(6, 0);   lcd.print(floatfrq,1);
       lcd.setCursor(13,0);   lcd.print("kHz");    
       break;
     case 6:   // above 1MHz
       lcd.setCursor(6, 0);   lcd.print(floatfrq,3);
       lcd.setCursor(13,0);   lcd.print("MHz");    
       break;       
  } 
}

void softReset(){
lcd.clear();
lcd.setCursor(0,0);
lcd.print("reset...");
delay(3500);
asm volatile ("  jmp 0");
}