the funny thing i just discovered is, the motor turns even if the machine 
is powered down, only when i pull the plug of the power supply, the motor 
shuts off

Am Donnerstag, 22. September 2016 19:37:19 UTC+2 schrieb Charles 
Steinkuehler:
>
> On 9/22/2016 12:21 PM, Sag ich Dir nich wrote: 
> > so now i added a scale (which is maximum rpm) and i can command various 
> speeds 
> > but still the motor vibrates. somehow it sounds like it ramps up and 
> down a bit 
> > when commanding for example 2000rpm. Noise could probably be, i may 
> change the 
> > output to another port (had some coordinate moves with various spindle 
> speeds 
> > and when one axis changed direction, the motor stopped for a few 
> milliseconds), 
> > is there any pin i can use for pwm that has 5v output on its own? 
>
> The PRU generated PWM output is fairly low frequency.  You may need to 
> increase the PWM frequency (which will decrease the available 
> resolution) or use one of the hardware PWM outputs.  I don't think 
> there is a HAL driver to talk directly to the BBB's hardware PWM 
> channels, but for spindle speed a user-mode python script should work 
> fine. 
>
> There is nothing on the BBB that generates a 5V output (3.3V only), 
> and no 5V buffered outputs on the CRAMPS boards (just the FET outputs). 
>
> If there is an analog input to your motor control, you could craft a 
> low-pass filter and the low-speed PWM wouldn't matter that much. 
>
> > what do you mean by "pull-up"? 
>
> A pull-up resistor to 5V.  A resistor between the FET output and the 
> power rail to pull the output high when the FET turns off. 
>
> -- 
> Charles Steinkuehler 
> cha...@steinkuehler.net <javascript:> 
>

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