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).
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.
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
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.
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-
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.