On Monday 01 June 2020 08:25:12 Dan Henderson wrote: > Chris, would think you would be able to connect the 0-10v output from > a BOB directly to the controller middle leg output of the > potentiometer. You wouldn’t need the hot leg, but would likely need > to ground the bob to the controller. > And that will break the mirror and let out all the smoke this stuff runs on and then none of it works. Certainly blowing the bob, possibly the computers port and various bits and pieces in the computer because the hot side of the line will then be connected to the computers ground.
Gizmo's like the spinx1 and pmdx-106 exist because 99.999% of those motor speed controllers have the adjustment pot tied to the hot side of the power line. Trying to connect a ground referenced control signal WILL let the smoke out of a lot of parts in them and in the computer. Nearly all of these things that do this computer control are run by a pwm modulated signal, which serves as a charge pump to develop the nominally 10 volt control signal, and then uses the average value of the PWM signal as the control signal, but its all isolated from that portion of the circuitry actually connected to the hot side of the power line. I have tried several variations of this basic idea on a card, with various results, most with control linearity problems that have been markedly improved with an isolation resistor in the 47k range between the cards 0 to 10 volt output, and the tie point the arm of the OEM pot is connected to, which if the circuit is analyzed, turns out to be the sum point of the feedback loop controlling the speed. And its a current sum, not voltage. Or was in those I've traced. That pmdx-106 is now a discoed product, works great when connected to the controller in the little hf mill. The spinx1 is very good also. > On Mon, Jun 1, 2020 at 12:13 AM Chris Albertson > <albertson.ch...@gmail.com> > > wrote: > > My cheap Harbor Freight mini mill has a variable speed spindle that > > is controlled by hand with a knob on the front of the mill. This > > knob turns a potentiometer. I think all mini mills work like > > this. > > > > Has anyone interfaced the potentiometer to LinuxCNC? I don't have > > the schematic for the spindle motor controller but I assume the > > potentiometer imply > > sends a control voltage to control the duty cycle of a PWM > > generator. The motor is a simple DC brushed motor > > > > It seems I could use the 0 - 10 volt output from a breakout board > > (with posible voltage conversion) to control the speed of the > > spindle. > > > > Then I place an encoder on the spindle. > > > > Has anyone made a simple interface that replaces the potentiometer? > > > > I don't want to rplace the spindle moter and use a VFD. I think > > this shold be very simple and low-cost. > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
