Mesa 7i78

COFHAL
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30 Aug 2021 18:57 #219183 by COFHAL

Replied by COFHAL on topic Mesa 7i78

Thank for you support. Other question:¿ the imput for this OP- amp is one PWM signal?

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PCW
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30 Aug 2021 19:04 #219184 by PCW

Replied by PCW on topic Mesa 7i78

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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COFHAL
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31 Aug 2021 14:06 #219249 by COFHAL

Replied by COFHAL on topic Mesa 7i78

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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PCW
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31 Aug 2021 14:13 #219250 by PCW

Replied by PCW on topic Mesa 7i78

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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COFHAL
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31 Aug 2021 14:25 #219252 by COFHAL

Replied by COFHAL on topic Mesa 7i78

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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PCW
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31 Aug 2021 14:43 #219255 by PCW

Replied by PCW on topic Mesa 7i78

What value potentiometer?

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COFHAL
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31 Aug 2021 14:53 #219256 by COFHAL

Replied by COFHAL on topic Mesa 7i78

10k

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PCW
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31 Aug 2021 15:05 #219258 by PCW

Replied by PCW on topic Mesa 7i78

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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COFHAL
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31 Aug 2021 15:08 #219259 by COFHAL

Replied by COFHAL on topic Mesa 7i78

This is the connection diagram to the spindle control card.

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COFHAL
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31 Aug 2021 15:14 - 31 Aug 2021 15:15 #219260 by COFHAL

Replied by COFHAL on topic Mesa 7i78

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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