Unable to set duty cycle to zero

[snagaitsev]

Describe the bug

I need to set and modify 16 PWM channels in order to create 16 PID controllers for heaters. The frequency is 5 Hz and I need to set the duty cycle in 1 ms steps, 0 to 200 ms.

If I set the duty cycle to 0%, I get a pulse 1 ms long every 200 ms (which is wrong as there should be no pulse at all). For the duty cycle = 1%, I get a pulse 3 ms (again wrong, it should be 2 ms), 2% -- 5 ms, …. 99% -- 199 ms, 100% -- 200 ms

Steps to Reproduce

https://github.com/snagaitsev/PWM_slow/blob/main/slow-pwm-test.ino

Expected behavior

There should not be any pulse at 0% duty cycle.

Actual behavior

At 5 Hz (same behavior happens at other frequencies like 50 Hz):
For the duty cycle of 0%, I get a pulse 1 ms long every 200 ms (which is wrong as there should be no pulse at all). For the duty cycle = 1%, I get a pulse 3 ms (again wrong, it should be 2 ms), 2% -- 5 ms, …. 99% -- 199 ms, 100% -- 200 ms

Debug and AT-command log (if applicable)

A clear and concise description of what you expected to happen.

Screenshots

If applicable, add screenshots to help explain your problem.

Information

Please ensure to specify the following:

Arduino 1.18.19
Teensyduino 1.56
Teensy slow PWM library 1.2.1
Teensy 4.0, 600 MHz
OS: Mint 20

[khoih-prog]

Hi @snagaitsev

It seems that you didn't use the higher uS resolution (default is mS) causing the counter to be imperfect.

Try to add

#define USING_MICROS_RESOLUTION     true

before

#include "Teensy_Slow_PWM.h"

such as in your modified code

/*
  Slow PWM test
*/

#define USING_MICROS_RESOLUTION     true

#include "Teensy_Slow_PWM.h"

#define HW_TIMER_INTERVAL_MS        0.01f
#define HW_TIMER_INTERVAL_FREQ      100000L

#define PIN_COUNT 16


int ssr0 = 3;
int ssr1 = 2;
int ssr2 = 5;
int ssr3 = 4;
int ssr4 = 7;
int ssr5 = 6;
int ssr6 = 9;
int ssr7 = 8;
int ssr8 = 11;
int ssr9 = 10;
int ssr10 = 14;
int ssr11 = 12;
int ssr12 = 18;
int ssr13 = 15;
int ssr14 = 22;
int ssr15 = 19;

// these are in ssr order
int pins[] = {
  3,
  2,
  5,
  4,
  7,
  6,
  9,
  8,
  11,
  10,
  14,
  12,
  18,
  15,
  22,
  19
};

// Init Teensy timer TEENSY_TIMER_1
TeensyTimer ITimer(TEENSY_TIMER_1);
// Init Teensy_SLOW_PWM, each can service 16 different ISR-based PWM channels
Teensy_SLOW_PWM ISR_PWM;

void TimerHandler()
{
  ISR_PWM.run();
}

int channels[PIN_COUNT];

float dutyCycles[PIN_COUNT];

float freq = 50.0f;

// the setup routine runs once when you press reset:
void setup() 
{
  Serial.begin(115200);

// Must be after attachInterrupt()
#if 0
  // initialize the digital pin as an output.
  for (int i = 0; i < PIN_COUNT; i++) 
  {
    pinMode(pins[i], OUTPUT);
    dutyCycles[i] = 0.0f;
    channels[i] = ISR_PWM.setPWM(pins[i], freq, dutyCycles[i]);
  }
#endif

  if (ITimer.attachInterrupt(HW_TIMER_INTERVAL_FREQ, TimerHandler)) 
  {
    Serial.println("Timer is good");
  } 
  else 
  {
    Serial.println("Timer is bad");
  }

  // initialize the digital pin as an output.
  for (int i = 0; i < PIN_COUNT; i++) 
  {
    pinMode(pins[i], OUTPUT);
    dutyCycles[i] = 50.0f;
    channels[i] = ISR_PWM.setPWM(pins[i], freq, dutyCycles[i]);
  }

  // Display 50% for 5s
  delay(5000);

  for (int i = 0; i < PIN_COUNT; i++) 
  {
    pinMode(pins[i], OUTPUT);
    dutyCycles[i] = 0.0;
    ISR_PWM.modifyPWMChannel(channels[i], pins[i], freq, dutyCycles[i]);
  }
}

bool dutySwitch = false;

// the loop routine runs over and over again forever:
void loop() 
{
  delay(2000);
}

[snagaitsev]

Thanks! It worked.

…

On Fri, Nov 4, 2022 at 1:13 PM Khoi Hoang ***@***.***> wrote: Hi @snagaitsev <https://github.com/snagaitsev> It seems that you didn't use the higher uS resolution (default is mS) causing the counter to be imperfect. Try to add #define USING_MICROS_RESOLUTION true before #include "Teensy_Slow_PWM.h" such as in your modified code /* Slow PWM test*/ #define USING_MICROS_RESOLUTION true #include "Teensy_Slow_PWM.h" #define HW_TIMER_INTERVAL_MS 0.01f #define HW_TIMER_INTERVAL_FREQ 100000L #define PIN_COUNT 16 int ssr0 = 3;int ssr1 = 2;int ssr2 = 5;int ssr3 = 4;int ssr4 = 7;int ssr5 = 6;int ssr6 = 9;int ssr7 = 8;int ssr8 = 11;int ssr9 = 10;int ssr10 = 14;int ssr11 = 12;int ssr12 = 18;int ssr13 = 15;int ssr14 = 22;int ssr15 = 19; // these are in ssr orderint pins[] = { 3, 2, 5, 4, 7, 6, 9, 8, 11, 10, 14, 12, 18, 15, 22, 19 }; // Init Teensy timer TEENSY_TIMER_1 TeensyTimer ITimer(TEENSY_TIMER_1);// Init Teensy_SLOW_PWM, each can service 16 different ISR-based PWM channels Teensy_SLOW_PWM ISR_PWM; void TimerHandler() { ISR_PWM.run(); } int channels[PIN_COUNT]; float dutyCycles[PIN_COUNT]; float freq = 50.0f; // the setup routine runs once when you press reset:void setup() { Serial.begin(115200); // Must be after attachInterrupt() #if 0 // initialize the digital pin as an output. for (int i = 0; i < PIN_COUNT; i++) { pinMode(pins[i], OUTPUT); dutyCycles[i] = 0.0f; channels[i] = ISR_PWM.setPWM(pins[i], freq, dutyCycles[i]); } #endif if (ITimer.attachInterrupt(HW_TIMER_INTERVAL_FREQ, TimerHandler)) { Serial.println("Timer is good"); } else { Serial.println("Timer is bad"); } // initialize the digital pin as an output. for (int i = 0; i < PIN_COUNT; i++) { pinMode(pins[i], OUTPUT); dutyCycles[i] = 50.0f; channels[i] = ISR_PWM.setPWM(pins[i], freq, dutyCycles[i]); } // Display 50% for 5s delay(5000); for (int i = 0; i < PIN_COUNT; i++) { pinMode(pins[i], OUTPUT); dutyCycles[i] = 0.0; ISR_PWM.modifyPWMChannel(channels[i], pins[i], freq, dutyCycles[i]); } } bool dutySwitch = false; // the loop routine runs over and over again forever:void loop() { delay(2000); } — Reply to this email directly, view it on GitHub <#1 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AKJ6SO4JIRBXCKFHJN2H6WDWGVG5VANCNFSM6AAAAAARXNCUUI> . You are receiving this because you were mentioned.Message ID: ***@***.***>