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Mesa 7i78
Mesa 7i78
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Posts: 228
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30 Aug 2021 18:57 #219183
by COFHAL
Thank for you support. Other question:¿ the imput for this OP- amp is one PWM signal?
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30 Aug 2021 19:04 #219184
by PCW
The input to the OP-AMP follower
is 2 pole filtered analog voltage where
100% PWM gives the full voltage between
SPINDLE+ and SPINDLE-
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31 Aug 2021 14:06 #219249
by COFHAL
According to that I can't use that output to control the speed of the spindle, and reading I don't see that other 7i78 compatible firmware could use it to generate a PWM signal that I can use to control the speed.
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31 Aug 2021 14:13 #219250
by PCW
Are you really sure the input impedance of your spindle speed control is 133 Ohms?
That make s no sense whatsoever. It would require something like a 10 Ohm potentiometer to be close to linear.
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31 Aug 2021 14:25 #219252
by COFHAL
Yes, If so,If so, I already did the test again with an analog potentiometer and it works perfectly. And with the PWM to DC card it worked perfect for me through the parallel port. Now that I am replacing the parallel port with the 7i92 with 7i78, this problem arises.
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Thank you received: 17
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Posts: 16978
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Thank you received: 4358
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31 Aug 2021 15:05 #219258
by PCW
Right so that means that the input impedance cannot be 133 ohms
(or you would get ~0.25V at 1/2 scale rather than 2.5V)
I suspect you have a missing connection ( you are likely
depending on the previous PWM devices lack of isolation )
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Posts: 228
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Thank you received: 17
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Posts: 228
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Thank you received: 17
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31 Aug 2021 15:14 - 31 Aug 2021 15:15 #219260
by COFHAL
This was the electronic circuit I used for the initial modification and it always worked.
Last edit: 31 Aug 2021 15:15 by
COFHAL.
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Mesa 7i78
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