Generating pulse and square wave

Official Hardware Classic UNO R4 WiFi
1

I am new to arduino development and I am trying to generate two syncronized waves on two different pins using an Arduino UNO R4 WIFI:

  • square wave 30 Hz 50% duty cycle
  • square pulse of 100µs synchronized on the rising edge of the square wave

I tried using delays and I was able to achieve the square wave, but not the pulse as it was not precise.

I am currently trying with two nested Fsp timers, but I am not able to make it work. Again, the square wave is correct, but the pulse does not occur every time it should.

Any type of guidance on the matter would be accepted.

Thank you in advance!

#include "FspTimer.h"

// Timer for the 30Hz square wave
FspTimer wave_timer;
uint64_t count = 0;
uint64_t start_time = 0;
int wave_pin = 5;
int wave_status = LOW;

// Timer for the 100us pulse
FspTimer pulse_timer;
int pulse_pin = 6; // New pin for the pulse output

// Callback method for the 30Hz square wave timer
void timer_callback(timer_callback_args_t __attribute((unused)) *p_args) {
  count++;
  if (!wave_status) {
    wave_status = HIGH;
    // On the rising edge of the 30Hz clock, start the pulse timer
    digitalWrite(pulse_pin, HIGH); // Set pulse pin HIGH
    pulse_timer.start();           // Start the pulse timer for 100us
  } else {
    wave_status = LOW;
  }
  digitalWrite(wave_pin, wave_status);
}

// Callback method for the 100us pulse timer
void pulse_timer_callback(timer_callback_args_t __attribute((unused)) *p_args) {
  digitalWrite(pulse_pin, LOW); // Set pulse pin LOW after 100us
  pulse_timer.stop();           // Stop the pulse timer
}

bool beginTimer(float rate) {
  pinMode(wave_pin, OUTPUT);
  pinMode(pulse_pin, OUTPUT); // Initialize pulse pin as output

  uint8_t timer_type = GPT_TIMER;
  int8_t tindex = FspTimer::get_available_timer(timer_type);
  if (tindex < 0) {
    tindex = FspTimer::get_available_timer(timer_type, true);
  }
  if (tindex < 0) {
    return false;
  }

  FspTimer::force_use_of_pwm_reserved_timer();

  // Setup the 30Hz audio timer
  if (!wave_timer.begin(TIMER_MODE_PERIODIC, timer_type, tindex, rate, 0.0f, timer_callback)) {
    return false;
  }

  if (!wave_timer.setup_overflow_irq()) {
    return false;
  }

  if (!wave_timer.open()) {
    return false;
  }

  if (!wave_timer.start()) {
    return false;
  }

  // Setup the 100us pulse timer
  // Get another available timer for the pulse
  int8_t pulse_tindex = FspTimer::get_available_timer(timer_type);
  if (pulse_tindex < 0) {
    pulse_tindex = FspTimer::get_available_timer(timer_type, true);
  }
  if (pulse_tindex < 0) {
    return false; // No available timer for pulse
  }

  // We want a 100us pulse, so the period is 0.0001 seconds.
  if (!pulse_timer.begin(TIMER_MODE_ONE_SHOT, timer_type, pulse_tindex, 10000.0f, 0.0f, pulse_timer_callback)) {
    return false;
  }

  if (!pulse_timer.setup_overflow_irq()) {
    return false;
  }

  if (!pulse_timer.open()) {
    return false;
  }

  // The pulse timer will be started in the audio_timer's callback
  return true;
}

void setup() {
  Serial.begin(115200);
  // Try to begin both timers
  if (!beginTimer(30)) {
    Serial.println("Failed to start timers!");
    while (1); // Halt if timers can't be started
  }
  start_time = millis();
  digitalWrite(pulse_pin, LOW); // Ensure pulse pin is low initially
}

void loop() {
  // calculate the effective frequency
  // This part of the code remains the same as it monitors the 30Hz clock
  int freq = 1000 * count / (millis() - start_time);
  Serial.println(freq);
  count = 0;
  start_time = millis();
  delay(1000);
}
2

so you tried something like this in loop:

  digitalWrite(pinA, HIGH);
  digitalWrite(pinB, HIGH);

  delayMicroseconds(100);
  digitalWrite(pinA, LOW);

  delayMicroseconds(16566); 
  digitalWrite(pinB, LOW);
  delayMicroseconds(16666);

and the 100us pulse wasn't ok?

3

Is it allowed that you use UNOR3 instead of UNOR4?

4

kmin,
Your suggestion looked pretty close to me:

Uno R4 30Hz 100µs
Uno R4 30Hz 100µs1024×600 11.1 KB

and the 100µs pulse on a faster time base:

Uno R4 100µs pulse 30Hz
Uno R4 100µs pulse 30Hz1024×600 11.2 KB

We need to know the pass/fail criteria for the 100µs being acceptable or not.

1 Like
5

No idea how to play with R4 timers, but I think with Esp32 it would be simple like this:

ledcAttachChannel(32, 30, 14, 0);
ledcAttachChannel(33, 30, 14, 1);

ledcWrite(32, 8192);
ledcWrite(33, 49);

50% duty on gpio32 and 0.3% duty on gpio33

6

Thank you for your answer.

Yes, indeed that was my first attempt and I could read the pulse on the oscilloscope every two or three rising edges of the square wave. I am starting to think the issue was with the oscilloscope and not with the code or the arduino...

I just checked again the code in my original post and it actually works as well (even though the frequency is not correct as it generates a 15Hz wave with 50% duty cycle).