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HELP: +/- Variable Voltage from uC

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sparky961:
Here's a circuit and simulated data, which is pretty much what I'm looking for.  The LM741 doesn't output full rail to rail voltage, hence the approx. +/-7.5 V output.

However, when I tried this in actual hardware the results didn't come close to the simulation.  <sigh>

If this were to work, it should only require 1 PWM output pin, plus the discrete resistors and small IC.  I'm not sure why it doesn't work though.

DMIOM:
Sparky,

Would there be any chance you share a bit more about the target? and about the accuracy you need? - is it for speed? or absolute position?

One of the reasons I ask is because I have had both servo drives and spindle inverters which both wanted +/- 10v and in both cases by reconfiguring the target I could get it to work with 0..10v and a logic input for direction (IIRC the inverter was ABB, can't recall the servo drive but it was Italian...)

If you do try and look at making your own by generating, say, 0-20v and then offsetting zero, you can get into all sorts of bother with both disparate ground/0v rails, and more especially/dangerously zero drift.

Dave

sparky961:
You were going in the right direction, Dave.  It's for controlling a BLDC Servo drive that wants a control signal in the range of +/- 10V.  It supplies a low current reference +10V and -10V that I think I could leverage but need the glue between that, the microcontroller, and the input.

The attached picture shows what's required and available from the servo drive.

DMIOM:
Sparky,

have you got any documentation for the BLDC drive?  Based on others I've seen, I would say there's a fighting chance there may be some jumper block / DIL switch / solder-bridge header / header for resistors in there.....

What sort of response rate & accuracy are you looking for?

Dave

sparky961:
I have some documentation for a slightly different model.  It mentions fine tuning with discrete components, but not changing the input voltage signal.  I've opened the case and also found no indications that the makers intended to have this changed.

As for accuracy & response rate, well, I'm aiming for as good as I can reasonably get.  That said, This will be part of a PID control loop, so I don't think it needs to be perfect.  The rest of the system should be able to compensate for minor errors.

I've simulated a non-inverting version of the op-amp circuit (yes, I've been hard at this all day now...) and it looks promising.  I'm going to reconfigure the hardware and see if it works any better.

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