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Ah.? Got it.? I've attached the updated drawing of the MACH3 Break Out Board from China.? My apologies to anyone who might have been confused by the schematic.

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The error is that I thought the P1 pin was driving the opto rather than what it really is doing is sinking current.? To make that work with MACH3 as the PWM, the Output Step line, which is P1, has to be inverted.

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So parameters are:? Spindle Step pulse P1, Spindle Direction P17 (which drives the relay on the board), Spindle Step pulse is inverted.

On the spindle setup screen the Use Spindle Output is checked along with PWM Control.

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Now when the P1 signal is logic high the opto output is off and a resistor pulls the input to the FET high which then turns on the FET which pulls the input to the opto buffer low and the PWM output is low.

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At 3000 RPM (Pulley #1 max speed) there's barely a pulse and the P1 is virtually low all the time pulling current through the opto input, turning on the opto output which pulls the FET drive low which turns off the FET.? The R17 resistor pulls the signal high and this into the op amp buffer results in 10V out the PWM pin.

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And in between we get a varying voltage now.

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Updated schematic attached.

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John

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I set up an older PC that had MACH2 since it has a parallel port.? Installed MACH3 on it and just got things rolling.? Need to bring the scope over.? With the meter it looks like it's all working correctly but hard to tell.

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Have to run out for a while but I'll report back with the details.