Hi,
I made some changes to improve accuracy and stability of the readings.
Unfortunally, the interrupt handler function delays the count. So, the maximum accurate frequency reading is about 98 KHz.
But bellow that frequency, the accuracy is very satisfactory. Minimum frequency is about 8 Hz.
Enjoy it! Thanks Rodmcm!
OBS: connect input pin only after reset, or ESP32 will enter in a loop...
Code: Select all
/*
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
Modified by Gustavo Murta
date : 17/jun/2020
https://www.esp32.com/viewtopic.php?f=19&t=6533
*/
const byte interruptPin = 23; // Assign the interrupt pin
volatile uint64_t StartValue = 0; // First interrupt value
volatile uint64_t PeriodCount; // period in counts
float Freq; // frequency
hw_timer_t * timer = NULL; // pointer to a variable of type hw_timer_t
//=======================================
void IRAM_ATTR handleInterrupt()
{
uint64_t TempVal = timerRead(timer); // value of timer at interrupt
PeriodCount = TempVal - StartValue; // period count between rising edges
StartValue = TempVal; // puts latest reading as start for next calculation
}
//======================================
void setup()
{
Serial.begin(115200);
pinMode(interruptPin, INPUT); // sets pin as input
attachInterrupt(interruptPin, handleInterrupt, FALLING); // attaches pin to interrupt on Falling Edge
timer = timerBegin(0, 2, true); // configure timer
// 0 = first timer
// 2 is prescaler so 80 MHZ divided by 2 = 40 MHZ signal
// true - counts up
timerStart(timer); // starts the timer
}
void loop()
{
Freq = 40000000.00 / PeriodCount; // calculate frequency
Serial.print("Frequency "); Serial.println(Freq, 0);
delay(250);
}
