Skip navigation
TechXchange
Digi-Key TechXchange Communities > Projects and Designs > Discussions
Up to Discussions in  Projects and Designs
8919 Views 4 Replies Latest reply: May 10, 2012 8:20 AM by MikeWeed RSS
KC Novice
KC
Currently Being Moderated

May 7, 2012 8:41 AM

Need help providing a variable voltage output 0-10VDC

I'm trying to manage a hydraulic pump using an Arduino microcontroller.  The hydraulic pump is controlled by a Hydraforce 4000165 Proportional valve controller that outputs current to the pump based on a VDC input 0-10VDC.

 

I need a way (or device) that can take a digital signal from the Arduino and convert it to a voltage 0-10VDC to maange the pump controller.  The input resistence of the pump controller is 225Kohm so the device needs to supply up to about 50 mircoamps.

 

This doesn't need to be high frequency (maybe 5 cycle/ second) or many increments of voltage (could probably do with outputting control coltages in 1V steps for at total of 11 steps between (0 and 10V).

 

Any suggestions?

 

Thanks-

  • Mike Novice
    Mike
    8 posts since
    Mar 31, 2011
    Currently Being Moderated
    May 7, 2012 8:31 PM (in response to KC)
    Re: Need help providing a variable voltage output 0-10VDC

    The first thing that comes to mind would be a digital potentiometer. As long as you can provide a 10V source, it should work fine. Based on your requirements, I would suggest about 100k value. Here is a possibility.

    • MikeWeed Novice
      MikeWeed
      51 posts since
      Oct 21, 2011
      Currently Being Moderated
      May 8, 2012 10:10 AM (in response to Mike)
      Re: Need help providing a variable voltage output 0-10VDC

      The source impedance of the digital pot must be much less than the input impedance of

      the controller or else you will lose a significant part of the signal in the source. A 100k

      pot will not work for a load impedance of 225k. A simple fix is to use a rail-to-rail op

      amp connected for unity gain between the pot and controller. I like the LMC6482 for this

      purpose.

      If you don't want to mess with a SPI interface, you might try something like the

      MAX7524. This has an 8 bit input, but you can drive the high 4 bits directly from

      the microprocessor and ground the low 4 bit inputs to get 16 analog voltage steps.

      This chip will probably also require a buffer amp. See the application notes.

      • KC Novice
        KC
        2 posts since
        May 7, 2012
        Currently Being Moderated
        May 10, 2012 6:44 AM (in response to MikeWeed)
        Need help providing a variable voltage output 0-10VDC

        Mike, thank you very much.  I built micro controller/ digital devices in the early nineties and now i've volunteered to help some local high school kids build a project. It's proving to be a little harder to bring it all back from the memory banks than I expected.

         

        Yes, I'd prefer this to be as simple as possible and don't want to deal with an SPI.  I don't remember how a pot works well enough to understand the significnce of the 100K digital pot versus the 10K and 50K ohm that are also available.

         

        Your suggestion of a DAC (you wrote MAX7524, which I presume you meant MX7524) seems like a great idea. 

         

        Question: the note for this device state "In applications requiring voltag output, an output operational amplifier and reference will be needed".  Is that what you mean by a "buffer amp" or is the buffer amp something different?  If the op amp and the buffer amp or the same, then would you recoommend the LMC 6482 for the MX7524 as well?

         

         

        Thank you very much-

         

        Kevin

        • MikeWeed Novice
          MikeWeed
          51 posts since
          Oct 21, 2011
          Currently Being Moderated
          May 10, 2012 8:20 AM (in response to KC)
          Need help providing a variable voltage output 0-10VDC

          Hi Kevin,

          Yes, I meant MX7524 (or MAX7624). The buffer amp and op amp are the same, shown as "A1"

          in "Typical Operating Circuit" on the MX7524 data sheet. Vref, Vdd and the amp supply

          voltage should all be +10V for your application, and connect -CS and -WR to ground

          to make the output continously follow the digital inputs. You will not need R1 or R2 or

          the 10 pF capacitor,  just connect the op amp output back to Vfeedback on the MX7524.

          Good luck!

          Mike

More Like This

  • Retrieving data ...

Bookmarked By (0)

Legend

  • Correct Answers - 4 points
  • Helpful Answers - 3 points