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Maybe I am way over my head here, but here it is:

I am trying to regulate a spindle RPM. The tachymeter part is now working flawlessly.

Now I am on the PID part, to control and regulate that speed. I am using the PID library on my Arduino Due. It "looks" like it works, but it does not.....

What I mean is that, if I measure with a multimeter the output directly from the Due, I can see the voltage increase steadily from a few millivolts up to 2.75/2.8 Volts, as it should.

BUT, if I measure after going through the logic level converter (as the spindle speed controler is for 5 volts), the voltage min is +- 1.3 volts (instead of a few millivolts), and max is 1.565 volts.

It's clearly not working as I thought it would. What am I missing here?

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    Can you show/describe your logic-level converter? Is it a chip, module with discrete components, breadboard, as well as how it's connected (schematic)? Nov 29 '17 at 15:23
  • It's the same as this one: ebay.com/i/262812423572?chn=ps&dispItem=1 I need a little more time to make a schema
    – BernardG
    Nov 29 '17 at 15:55
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    @Gerben yes, I did.
    – BernardG
    Nov 29 '17 at 16:12
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    And connected all grounds together? Can you provide a schematic? Nov 29 '17 at 16:14
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    Measuring a PWM wave (what I think is your output) is difficult with a multimeter. Can you try with an oscilloscope? Put one probe before and another after the level translator and compare them. If you can't, try "manually" switching the output (i.e. first let the arduino output a HIGH value, measure it, then a LOW value and measure it again)
    – frarugi87
    Nov 30 '17 at 8:31

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