PWM reading with DUE

Hardware Arduino Due
1

I need to read PWM signal - it's duty cycle and frequency

I try to use code published on:
http://www.benripley.com/diy/arduino/three-ways-to-read-a-pwm-signal-with-arduino/

The pulseIn() Function gives me very inaccurate results, and when I try to use <PinChangeInt.h> library, it shows error:
No such file or directory #include <new.h>

Is there some easy solution?

2

This really isn't an installation and troubleshooting sort of question. . .

The Due isn't AVR- based, and the pin change interrupt library is AVR-specific.

I'm surprised pulseIn isn't working for you, but you didn't post any code or schematic or expectations, so help is hard to give

3

@aixam, your topic has been moved to a more suitable location on the forum. Installation and Troubleshooting is not for problems with your project :wink: See About the Installation & Troubleshooting category.

1 Like
4

I posted in installation and troubleshooting because of
"No such file or directory #include <new.h>" error.

good to know that there might be a problem with using pin change interrupt library on DUE

I connected my DUE to ESP32, which provides PWM 50% duty cycle at 5000Hz, so pulsein() should show 100, but it reads different values from 100 to 149 and I can't have such a big error.

5

@aixam If your pulsewidths aren't any shorter than a microsecond then here's a way to measure pulsewidth:

// Sketch to calculate pulsewidth from an input signal in microseconds

#define INPUT_PIN 10                      // Arduino input pin number

volatile unsigned long isrPulsewidth;     // Define Interrupt Service Routine (ISR) pulsewidth
unsigned long pulseWidth;                 // Define Pulsewidth variable

void setup() 
{
  pinMode(INPUT_PIN, INPUT);              // Set the input pin
  attachInterrupt(digitalPinToInterrupt(INPUT_PIN), calcPulsewidth, CHANGE);   // Run the calcPulsewidth function on signal CHANGE
}

void loop() 
{
  noInterrupts();                         // Turn off interrupts
  pulseWidth = isrPulsewidth;             // Copy the isr pulsewidth to the pulsewidth variable
  interrupts();                           // Turn on interrupts
  // Work with pulsewidth here ...
  // ...
}

void calcPulsewidth()                    // Interrupt Service Routine (ISR)
{
  static unsigned long pulseStartTime;   // Start time variable
  
  if (digitalRead(INPUT_PIN) == HIGH)    // If the change was a RISING edge
  {
    pulseStartTime = micros();           // Store the start time (in microseconds)
  }
  else                                   // If the change was a FALLING edge
  {        
    isrPulsewidth = micros() - pulseStartTime;    // Calculate the pulsewidth
  }
}

The period (frequency) could be measured by storing the time between pulses in a similar fashion.

A more sophisticated option is to use timer capture detailed here: https://forum.arduino.cc/t/due-timer-capture-mode-tc0-channel-1/441820/4.

6

That's a programming issue - the file couldn't be found because it doesn't exist as far as the Due is concerned.

7

I have not used ESP32, but my experience with ESP8266 shows that it generates PWM software, not hardware. When checking the signal with an oscilloscope, large deviations are observed.

8

Sweet bike, by the way. I'm a rider myself.

9

Hi there @aixam

With tc_lib (https://github.com/antodom/tc_lib) you can measure the period and duty of a digital signal (like a PWM signal) using the DUE.

in this post you have more information about tc_lib:

The measurements are stable and can get to frequencies greater than 20 Mhz.
I hope it helps.

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10

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