-10 to +10 Volt Control (For Motor Controller)

JonnyMac

I'm assisting a friend with a project that needs a new motor controller. The motor control products we've found that are in his budget tend to be voltage controlled. For our end, we're going to use a Propeller to run the thing if we can get this all sorted out.

Analog stuff like this is not my bag, so I'm hoping a friend or two here can point me in the right direction so I can help my friend.

Phil Pilgrim (PhiPi)

Wouldn't a PWM'd H-bridge do the job? Nevermind. I misread. It's the motor controller that requires the +-10V, not the motor itself.

-Phil

Phil Pilgrim (PhiPi)

Jon, I think this circuit will work, but I'll test it to make sure:



-Phil

Phil Pilgrim (PhiPi)

Here's the circuit that eventually worked. I had to buffer the DUTY-mode input to get a full-scale output. And the pot has to be there to adjust for offset.



Here's what the output looks like, using the program shown below it:

CON

  _clkmode      = xtal1 + pll16x
  _xinfreq      = 5_000_000

VAR

  long  i

PUB  start

  dira[0]~~
  ctra := %00110 << 26
  repeat
    repeat i from 0 to $7fff_ffff step $80000
      frqa := i << 1

Mickster

Here is an alternative.

5v PWM @ 50% duty = 0v

Phil Pilgrim (PhiPi)

Mickster wrote:

5v PWM ...

The Propeller outputs a 3.3V DUTY/PWM.

-Phil

Mickster

Phil Pilgrim (PhiPi) wrote: »

Mickster wrote:

5v PWM ...

The Propeller outputs a 3.3V DUTY/PWM.

-Phil

Oh sure but when interfacing to industrial servo drives and I/O, I opto-couple everything and I use a separate 5v PSU for the isolated stuff. +/- 10v is the standard motor command in my world.

Phil Pilgrim (PhiPi)

Your opto output would have to be push-pull for your circuit to work without an input buffer. Most optos are open-collector/open-drain.

-Phil

Mickster

Hmmm, don't remember the specifics. It's been many years since we used the LM629 motion chip which gave us no-end of trouble until we isolated the PWM. Funnily enough, I only had that image because a customer was asking if he could modify it to accommodate an offset pot....something that you already thought of

Peter Jakacki

Just use a single opamp in the non-inverting config, I've done it heaps of times. One resistor for gain, none for offset. (The values shown are for 0-3V in but if you use two resistors in series it is very easy to trim to an exact value )

Try 6k8 for R2 and then 12k + 1k8 for a gain of 3.03 * 3.3V = 9.997V