Mesa 7i78

PCW
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28 Aug 2021 17:26 #219033 by PCW

Replied by PCW on topic Mesa 7i78

Then I suspect something else is wrong
A potentiometer circuit would not have a 133 Ohm load

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COFHAL
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28 Aug 2021 17:33 - 28 Aug 2021 17:35 #219035 by COFHAL

Replied by COFHAL on topic Mesa 7i78

I don't think so because if I use an analog potentiometer I can control the speed of the spindle. Previously I used this PWM to DC converter circuit and it works perfect.

Last edit: 28 Aug 2021 17:35 by COFHAL.

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COFHAL
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28 Aug 2021 17:37 #219036 by COFHAL

Replied by COFHAL on topic Mesa 7i78

I removed it to use the spindle output that the 7i78 brings.

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PCW
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28 Aug 2021 17:47 #219038 by PCW

Replied by PCW on topic Mesa 7i78

That circuit does not appear to be isolated.

Is it possible you were depending on a common
connection that does no exist in the 7I78s output
because the 7I78s analog output is isolated?

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COFHAL
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28 Aug 2021 18:01 #219040 by COFHAL

Replied by COFHAL on topic Mesa 7i78

It could be that, anyway, thank you very much.

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COFHAL
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28 Aug 2021 18:04 #219041 by COFHAL

Replied by COFHAL on topic Mesa 7i78

What IC does the 7i78 use for the isolated potentiometer?

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COFHAL
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30 Aug 2021 14:11 #219170 by COFHAL

Replied by COFHAL on topic Mesa 7i78

I already checked the speed control card of my spindle and found that the input of the analog potentiometer is an ADC of an ATEMGA8 microcontroller, possibly that is the reason for the low resistance that this input presents.

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PCW
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30 Aug 2021 17:37 #219178 by PCW

Replied by PCW on topic Mesa 7i78

I would expect an microcontroller analog input to have a very high input impedance
( >100K ohms )

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COFHAL
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30 Aug 2021 18:38 #219181 by COFHAL

Replied by COFHAL on topic Mesa 7i78

Yes but not, which IC does the 7i78 use as a digital potentiometer?

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PCW
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30 Aug 2021 18:55 #219182 by PCW

Replied by PCW on topic Mesa 7i78

The output OP-Amp is a NE5230/NCV5230. It has a 100 Ohm series resistor in its output for stability into capacitive loads

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Mesa 7i78

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