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/*
Measures the frequency of a square wave appliet to a digital input
Uses a free running timer/counter for the period measurement
by: rodmcm
date: 25/7/2018
*/
const byte interruptPin = 23; // Assign the interrupt pin
volatile uint64_t StartValue; // First interrupt value
volatile uint64_t PeriodCount; // period in counts of 0.000001 of a second
float Freg; // frequency
char str[21]; // for printing uint64_t values
hw_timer_t * timer = NULL; // pointer to a variable of type hw_timer_t
portMUX_TYPE mux = portMUX_INITIALIZER_UNLOCKED; // synchs between maon cose and interrupt?
// Digital Event Interrupt
// Enters on falling edge in this example
//=======================================
void IRAM_ATTR handleInterrupt()
{
portENTER_CRITICAL_ISR(&mux);
uint64_t TempVal= timerRead(timer); // value of timer at interrupt
PeriodCount= TempVal - StartValue; // period count between rising edges in 0.000001 of a second
StartValue = TempVal; // puts latest reading as start for next calculation
portEXIT_CRITICAL_ISR(&mux);
}
// Converts unit64_t to char for printing
// Serial.println(uintToStr( num, str ));
//================================================
char * uintToStr( const uint64_t num, char *str )
{
uint8_t i = 0;
uint64_t n = num;
do
i++;
while ( n /= 10 );
str[i] = '\0';
n = num;
do
str[--i] = ( n % 10 ) + '0';
while ( n /= 10 );
return str;
}
// SetUp
//======================================
void setup()
{
Serial.begin(115200);
pinMode(interruptPin, INPUT_PULLUP); // sets pin high
attachInterrupt(digitalPinToInterrupt(interruptPin), handleInterrupt, FALLING); // attaches pin to interrupt on Falling Edge
timer = timerBegin(0, 80, true); // this returns a pointer to the hw_timer_t global variable
// 0 = first timer
// 80 is prescaler so 80MHZ divided by 80 = 1MHZ signal ie 0.000001 of a second
// true - counts up
timerStart(timer); // starts the timer
}
void loop()
{
portENTER_CRITICAL(&mux);
Freg =1000000.00/PeriodCount; // PeriodCount in 0.000001 of a second
portEXIT_CRITICAL(&mux);
Serial.print("Frequency ");Serial.println(Freg,2);
delay(200);
}
