Thread: -10V to 10v circuit
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14-01-2014 #11
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14-01-2014 #12
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14-01-2014 #13
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14-01-2014 #14
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14-01-2014 #15
Don't be silly now, you know how to do that. Also this thread is going off the rails due to lack of info from the OP, he's either controlling a servo driver or a VFD. The VFD is straight forward, use a spindle board from Mach3, the servo driver, who knows until more info is given ?
Anyway I'm only looking at novel ways to derive a -10v to +10v output but nobody wants to play about with it or forward their own ideas.
It's one of those days when I'm thinking, why bother ?Last edited by EddyCurrent; 14-01-2014 at 06:13 PM.
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14-01-2014 #16
Thank you for all answers.
I will use linuxcnc not mach3 because mach3 does not have the ability to make outer close loop (not real time kernel in windows).
The servos are for a lathe retrofit ( x & z axes) and the vfd is to control the spindle speed and direction (cc or ccw)
The servo has a mode position/speed and from an input signal you can select position or speed (step/dir or analog -10 to +10v).
I want to have the ability to override the speed manually outside from gcode so this is the reason why i want analog -10v to +10v.
Also i want to control vfd from gcode to have constant surface speed and i want to override this speed manually.
Because with parallel port hardware limit exits and i can't output 500khz pulse train (2500cpr encoder) i want a card to manage 500khz step/dir signals.
Do you know some card which can do this work in linux and cooperate with linuxcnc ?
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14-01-2014 #17
Eddy - I don't think that it's very novel, but to go from 0-5V to -10-10V I would use an op amp in a similar way to the link that Jonathan gave. Personally, I would do it slightly differently; the op amp needs +-12V to make sure that there is enough headroom on the output (unless you find an op amp that can work closer to the supply rails). Use a potential divider across the supply rails (or +12 and 0V), with whatever regulation/zener diode etc you like, to give a fixed 2.5V and connect this to the inverting input via R1. Use a feedback resistor R2 from output to inverting input. R2/R1 = 4 to give correct gain. Take the 0-5V via an appropriate resistor to the non-inverting input. Job done - I think. You could incorporate a bit more smoothing if you are using a PWM analogue "pseudo 0-5V" signal by putting a suitable capacitor in parallel with the feedback resistor.
You would then use this on a 0-5V output from a BOB connected to the LinuxCNC system and LCNC would allow either gcode-controlled speed or could be overridden for manual control from the LCNC control panel. I think - I use LinuxCNC but don't have speed control that way yet (just use VFD controls manually) so I'm not familiar with that bit.
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15-01-2014 #18
I think you're still confusing analogue servo operation with step/direction.
You can use the servo
a) with analogue voltage control and encoder feedback for closed loop positioning OR
b) with step/direction pulse train open loop or closed loop with encoder feedback
You can't use step/direction AND analogue voltage together, they are different operating modes of the servo amplifier/driver. A CSMIO/IP motion control card will do what you need and works with Mach3 (it does closed loop control outside of Mach3), don't know about LinuxCNC: the CSMIO/IP-S will do step/direction, the CSMIO/IP-A will do +/-10v analogue. Both will provide the spindle VFD speed/direction output.
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