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PWM Divider advice

 
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yongkimleng



Joined: 22 Sep 2009
Posts: 7

PostPosted: Thu Oct 01, 2009 12:18 pm    Post subject: PWM Divider advice Reply with quote

Hi,

I found that the PWM divider affects the electrical stability of the openservo setup by a huge margin. My setup was very unstable when the divider was 0x10, somewhat stable at 0x40 and very stable at 0x60-0x80.

I have measured that my motor coil resistance is 25.6 ohms and it is rated for 6v operation but I'm using 9v while ensuring that the PWM value in the openservo code does not go above 170 (out of 255).

Does anyone have any advice why it behaves this way?

Thanks in advance

Best regards,
James
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davidbeckam



Joined: 23 Sep 2009
Posts: 1

PostPosted: Thu Oct 01, 2009 2:25 pm    Post subject: HELP.. Reply with quote

I understand the pwm output on the arduinos is 0-5V. Is there a way i could make this voltage go from 0-10V?

Would a king of voltage doubler circuit work on the end of the output. Similar to a voltage divider, but a multiplier instead???
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jharvey
co-admin


Joined: 15 Mar 2009
Posts: 359
Location: Maine USA

PostPosted: Thu Oct 01, 2009 9:10 pm    Post subject: Reply with quote

About the voltage doubling idea, I think the problem there is space. It would be hard to fit on the PCB. I think you would be better off putting on a huge cap to help buffer instead.

About the PWM, I believe the PWM divider will allow the PWM duty to streach out. If you had a scope on it, I believe you would see a huge inrush. When the PWM is set high enough, that inrush is limited, such that you don't brown out.

So 9v/26ohms is .346 amps DC, while the impeadance is some other resistance, this will allow for a higher current draw when first turned on, which will eventually settle to .346 amps.

I'd bet a larger input buffer cap would allow for lower PWM dividers.
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newyorkdd



Joined: 14 Jul 2011
Posts: 2

PostPosted: Thu Jul 14, 2011 6:22 am    Post subject: Reply with quote

hi,

I am also looking answer for
I understand the pwm output on the arduinos is 0-5V. Is there a way i could make this voltage go from 0-10V?
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Janleex0



Joined: 30 Jan 2014
Posts: 1

PostPosted: Thu Jan 30, 2014 6:58 am    Post subject: Reply with quote

I am using a Futaba-Servo with PCB replaced to OpenServo V2, bought from watterott (sorry, but I can't type link on my first post).
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