/*
* 3/29/2018 - Devon Bray - https://www.esologic.commultiple-frequency-counter-arduino/
*
* I've written most of the important notes as comments in the source, but a couple more details:
*
* - The important data is stored in `period_averages_ms` and `frequency_averages_hz`. You address them using the indices defined at the top of the file. These arrays get updated each time `compute_counts()` is called. Keep it `compute_counts()` somewhere in the main() loop.
*
* - You could easily add more frequencies, you just have to `NUMSIGS`, make a specific ISR, and another `attachInterrupt` line in setup()
*
* - It uses [interrupts](https://playground.arduino.cc/Code/Interrupts) which might not be right for your proejct, but normally shouldn't get in the way of too much stuff.
*
* - If the ISR hasn't seen a new edge in 1000000us, both `period_averages_ms[p_index]` and `frequency_averages_hz[p_index]` will be set to zero!
* - This means that slowest frequency that this code can detect is 1hz!
*
*/
int freq_pin_1 = 2; // the pin connected to the first signal, must be an interrupt pin! See the arduino docs
int freq_pin_2 = 3; // the pin connected to the second signal, must be an interrupt pin! See the arduino docs
#define BUFFSIZE 100 // a rolling average of the frequency/period is computed, and this is the size of that buffer
#define NUMSIGS 2
#define FREQ1INDEX 0
#define FREQ2INDEX 1
volatile int period_buffer_indices[NUMSIGS] = { 0 }; // the location of the index for adding to the rolling buffer average
volatile unsigned long period_buffers[NUMSIGS][BUFFSIZE] = { 0 }; // the buffers
volatile unsigned long previous_edge_times_us[NUMSIGS] = { 0 }; // the time that the previous edge came in in microseconds
volatile float period_averages_ms[NUMSIGS] = { 0 }; // the period time of a given signal in milliseconds
volatile float frequency_averages_hz[NUMSIGS] = { 0 }; // the frequency of a given signal in hertz
volatile bool period_buffer_locked[NUMSIGS] = { false }; // spin locks for the different buffers
void setup() {
Serial.begin(9600);
// the pins must be mapped to their ISRs
pinMode(freq_pin_1, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(freq_pin_1), new_freq1_edge, RISING); // you could change this mode to whatever you were looking for, FALLING, CHANGE etc.
pinMode(freq_pin_2, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(freq_pin_2), new_freq2_edge, RISING);
}
void loop() {
compute_counts();
Serial.print("Pin 1: ");
Serial.print(period_averages_ms[FREQ1INDEX]);
Serial.print("ms, ");
Serial.print(frequency_averages_hz[FREQ1INDEX]);
Serial.print(" hz");
Serial.print(" - Pin 2: ");
Serial.print(period_averages_ms[FREQ2INDEX]);
Serial.print("ms, ");
Serial.print(frequency_averages_hz[FREQ2INDEX]);
Serial.print(" hz");
Serial.println("");
}
void compute_counts() {
// computes the average of the buffer for a given signal. Must be called before using the period_averages_ms or frequency_averages_hz buffers.
for (int p_index = 0; p_index < NUMSIGS; p_index++) {
float buffer_sum = 0;
while (period_buffer_locked[p_index]) {}; // wait around for the ISR to finish
period_buffer_locked[p_index] = true; // ISR won't add new data to `period_buffers`
if ((micros() - previous_edge_times_us[p_index]) < 1000000) {
for (int j = 0; j < BUFFSIZE; j++) {
buffer_sum += period_buffers[p_index][j];
}
}
period_buffer_locked[p_index] = false; // ISR will now add new data to `period_buffers`
if (buffer_sum > 0){
period_averages_ms[p_index] = ((buffer_sum / (float)BUFFSIZE)) / 1000;
frequency_averages_hz[p_index] = (1 / period_averages_ms[p_index]) * 1000;
}
else {
period_averages_ms[p_index] = 0;
frequency_averages_hz[p_index] = 0;
}
}
}
void new_edge(int period_index) {
unsigned long current = micros();
if (period_buffer_locked[period_index] == false) { // if compute_counts is using the buffer, skip adding to it because that process isn't atomic
period_buffer_locked[period_index] = true;
period_buffers[period_index][period_buffer_indices[period_index]] = current - previous_edge_times_us[period_index];
period_buffer_locked[period_index] = false;
period_buffer_indices[period_index]++;
if (period_buffer_indices[period_index] >= BUFFSIZE) {
period_buffer_indices[period_index] = 0;
}
}
previous_edge_times_us[period_index] = current; // but make sure the new time is set because this operation is atomic
}
void new_freq1_edge() {
new_edge(FREQ1INDEX);
}
void new_freq2_edge() {
new_edge(FREQ2INDEX);
}
