Map()ing PWM to Millis(() is that possible?

[attiny85nightmare]

Hello, I am trying to start/stop a dc motor in a smooth way, and I remember I read and bookmarked a site where they had a code snippet to use map() and millis(() over a value of PWM to soft stop a motor in a given period of time. But I cannot find it anymore in my bookmark's list ! So I tried to make an basic seudocode like:

pwmVal=map( pwmVal, startingMillis,finishingMillis,givenPWM,255)

while keeping track of the millis() passed. My dc motor stop with 255 pwm value and keeps running with lower values.

let say I want the motor goes from running to full stop in 5 seconds.

So do you think guys is this feasible ? I don't have any code yet,just the general idea but not sure if this is the right way to do it.
Thanks in advance!

[UKHeliBob]

If the PWM output needs to change from 255 to 0 over a period of 5 seconds then you need to decrease the value written to the PWM output by 1 about every 20 milliseconds (5000/255)

Using the BlinkWithoutDelay timing method with a period of 20 milliseconds, when each period ends reduce the PWM output by 1 until it reaches zero

[killzone_kid]

pseudo code

start = millis();
end = start + 5000;
loop
{
analogWrite(map(millis(), start, end, 0, 255));
}

[attiny85nightmare]

@UKHeliBob

If the PWM output needs to change from 255 to 0 over a period of 5 seconds then you need to decrease the value written to the PWM output by 1 about every 20 milliseconds (5000/255)

Using the BlinkWithoutDelay timing method with a period of 20 milliseconds, when each period ends reduce the PWM output by 1 until it reaches zero

Actually the output must go from a working pwm value (motor is running) to 255 (motor stopped) cos my driver has inverted logic, so I get the idea, it just that map()/millis() solution looked so simple to implement ina couple of lines, sadly i cannot figure out how it was done . So doing my own math and timing is the way to go right?

[attiny85nightmare]

@killzone_kid

pseudo code

start = millis();
end = start + 5000;
loop
{
analogWrite(map(millis(), start, end, 0, 255));
}

yes, something like that! I know map loose some precision in the process but is not that a big deal in my case, just need a smooth stop. so I will try both solutions this nite and see how things go! will be back! thank you!

[johnwasser]

  unsigned long startFade = millis();
  const unsigned long fadeDuration = 5000;
  while (millis() - startFade < fadeDuration)
  {
    int pwm = map(millis() - startFade, 0, fadeDuration, startPWM, endPWM);
    analogWrite(MotorPin, pwm);
  }

[attiny85nightmare]

Done! For simplicity I made startFade = 0; and replaced while for if,so now I'm ready to stop the motor when it is needed, I thought I understood well the map() function but I was wrong, interesting enough, I see that the implicit variable to map (millis()-startFade) in this case, is not always the output variable that I will use to set the pin to pwm the motor as I did in my first post: pwmVal=map( pwmVal, startingMillis,finishingMillis,givenPWM,255)