BowstringLakeDavid
Posts: 1
Joined: Thu Aug 27, 2015 2:59 pm

PWM pulse widths, duty cycles and Freqs

Thu Aug 27, 2015 3:09 pm

Can anyone clue me in as to what the minimum pulse width, maximum frequency, maximum and minimum duty cycle can be using Raspberry Pi B+ (I'm not interested in overclocking or anything like that)
Thank you
(if this isn't the right forum to ask please let me know where)

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joan
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Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: PWM pulse widths, duty cycles and Freqs

Thu Aug 27, 2015 4:15 pm

That depends on how you want to generate the PWM. You will get more flexibilty if you generate your own PWM.

minimum pulse width: 8 nanoseconds
maximum frequency: 125 MHz
maximum and minimum dutycycle: arbitrary

jdb
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Joined: Thu Jul 11, 2013 2:37 pm

Re: PWM pulse widths, duty cycles and Freqs

Thu Aug 27, 2015 7:03 pm

If you (ab)use the PWM peripheral in serial output mode coupled with a cyclic DMA transfer, you effectively have an arbitrary waveform generator at any bandwidth up to ~100MHz.

Getting a GPIO pin to go that fast, however, is an entirely different kettle of fish.
Rockets are loud.
https://astro-pi.org

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cyrano
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Location: Belgium

Re: PWM pulse widths, duty cycles and Freqs

Sun Aug 30, 2015 10:09 pm

BowstringLakeDavid wrote:Can anyone clue me in as to what the minimum pulse width, maximum frequency, maximum and minimum duty cycle can be using Raspberry Pi B+ (I'm not interested in overclocking or anything like that)
Thank you
(if this isn't the right forum to ask please let me know where)
That depends entirely on your application. Driving a hefty AC/DC motor requires other settings than driving a servo, a stepper motor or some LED's.

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