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Topic: How fast does PWM actually need to pulse.... (Read 696 times) previous topic - next topic

JimboZA

.... to fool the device into thinking it's getting voltage lower than the maximum, as opposed to getting a series of discrete ons and offs?

If I hook a motor up to a battery through a manual switch and switch it off and on every 30 seconds, in theory that's PWM but too slow to fool the motor. The motor will run for 30 seconds at whatever speed it gets to for that battery, then go off for 30 seconds.

I suppose it depends on the device?- an LED might get to full brightness in a much shorter time than a device with inertia like a motor would get to full speed.

Just curious.....
Roy from ITCrowd: Have you tried turning it off an on again?
I'm on LinkedIn: http://www.linkedin.com/in/jimbrownza

Magician

You are right with motors. LED is lighting up instantly, but your brain is slow to notice it for a few milliseconds, so PWM frequency does not have to be very high.

MAS3

Also, starting a motor takes a higher duty cycle than keeping it running.
Start speed of a motor or valve has always been higher than the minimal running speed of that motor or the smallest opening of a valve for the uses i have seen yet.
This however has little to do with the frequency, which is what you asked for.
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

fungus


I suppose it depends on the device?- an LED might get to full brightness in a much shorter time than a device with inertia like a motor would get to full speed.

Just curious.....


I think you answered your own question. Optimum rate will depend on the device.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

JimboZA

Roy from ITCrowd: Have you tried turning it off an on again?
I'm on LinkedIn: http://www.linkedin.com/in/jimbrownza

AWOL

Quote
If I hook a motor up to a battery through a manual switch and switch it off and on every 30 seconds, in theory that's PWM but too slow to fool the motor. The motor will run for 30 seconds at whatever speed it gets to for that battery, then go off for 30 seconds.
but, you have to admit, the average RPM over that time will reflect the supply duty cycle  ;)
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

JimboZA

Quote
but, you have to admit, the average RPM over that time will reflect the supply duty cycle 


True
Roy from ITCrowd: Have you tried turning it off an on again?
I'm on LinkedIn: http://www.linkedin.com/in/jimbrownza

cyclegadget


I have worked with some motors that produced over 25,000 HP and took more than 2 minutes to come to a stop after the power was removed. It took about 10 seconds to go from 0 to 1200rpm with full voltage applied to it.
Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

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