Electronics Design Group Assignment

observe the operation of a microcontroller circuit board

We want to measure the PWM. To do this, we use the sample program Fade and select pin 7 on our board.

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change the sketch fade to measure pwm

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For the Arduino IDE we have to specify pin 6.

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int led = 6;           // the PWM pin the LED is attached to
int brightness = 0;    // how bright the LED is
int fadeAmount = 5;    // how many points to fade the LED by

// the setup routine runs once when you press reset:
void setup() {
  // declare pin 6 to be an output:
  pinMode(led, OUTPUT);
}

// the loop routine runs over and over again forever:
void loop() {
  // set the brightness of pin 9:
  analogWrite(led, brightness);

  // change the brightness for next time through the loop:
  brightness = brightness + fadeAmount;

  // reverse the direction of the fading at the ends of the fade:
  if (brightness <= 0 || brightness >= 255) {
    fadeAmount = -fadeAmount;
  }
  // wait for 30 milliseconds to see the dimming effect
  delay(30);
}

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With the programmer we now load the sketch onto the board.

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The led gets lighter and darker.

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measure what happens on the board

If we now look at the current flow on the oscilloscope, the PWM becomes readable. We have about 2 boxes from rising edge to rising edge. this corresponds to 4ms. This results in a frequency of 1 / 0.004, i.e. 250 Hz.