Controlling feed with potentiometer

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13 Jun 2015 02:23 #59758 by DaPeace
Is it possible to use one of the LPT-in to control the feed-override by a potentiometer?
Im a little in to electronics and it wouldnt be a problem to map the poti to a pwm-signal and input it with a small microcontroller.
But i didnt find any informations around the net and thought i will simply ask here..

Thank you,
Jan

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13 Jun 2015 02:48 #59759 by alan_3301

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13 Jun 2015 02:53 #59760 by DaPeace
Thats not very specific. I know that its possible to use it but my main problem is that ive not found anything if it is possible to input pwm to the input-pins of the lpt and how to handle the signal.


Thanks anyways

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13 Jun 2015 03:00 #59761 by PCW
you could use a cheap Voltage to Frequency converter (say a 555) and then use an
encoder component ( with just the 'A' pin) in HAL to read the frequency (encoder velocity)

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13 Jun 2015 03:34 #59762 by alan_3301
you should be able to send the potentiometer output straight to the input pin, and scale it in hal I would think.

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13 Jun 2015 03:35 #59763 by andypugh

Is it possible to use one of the LPT-in to control the feed-override by a potentiometer?


It's _much_ easier to use an encoder. Something like:
www.ebay.at/itm/291487578363

One possibility for analogue input (that I have never tried) would be to use a PWM output into a filter, and then a comparator to indicate that the values are equal.
(so it needs an input pin and an output pin)

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13 Jun 2015 03:43 #59764 by DaPeace
Oh ok. Didnt see potis like that.. thats really easy. so hooking up a poti like that to the lpt-input would be possible without additional hardware?
What configs do i need in the hal-files? is there a tutorial or wiki around where i could read around a bit?
Thank you

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13 Jun 2015 03:47 #59766 by alan_3301
Ok maybe I was steering you wrong, it looks like the parallel port pins are digital only.

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13 Jun 2015 03:51 #59769 by andypugh

Oh ok. Didnt see potis like that.. thats really easy. so hooking up a poti like that to the lpt-input would be possible without additional hardware?


Yes, you would use two inputs as the A and B phases to an encoder component in HAL.
linuxcnc.org/docs/html/man/man9/encoder.9.html

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25 Jun 2015 23:13 #60132 by DaPeace
Hello.. its me again. Ive tried to adapt the code from here but i cant get it to work.
I can see that the hal-pins of channel a + b are changing while turning the encoder but the count is not counting and so the feed is not changing. Also tried with spindle-overwrite like in the example but thats not working too.
Any help in that case?
Maybe some code-examples?

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