General Purpose Analog Output

Robotics and electronics discussion Electronics
1

Hi all,

We currently have an application where we need to output a controlled 0V-10V signal, and I’m looking for a suggestion as to the best way to provide this variable output voltage (not sure if I can use an existing board, or if I need something like a digital POT to attach to an existing board).

We have a servo-controlled valve that we would like to drive from a micro controller (or servo/motor controller - I really like the Maestro due to its simple on-board scripting). The problem is that the valve does not expose the servo control direclty, but rather, has its own components for servo control and expects only a raw voltage across two pins in order to function. Supplying 0V puts the valve in the “close” position, 5V in “half-open” and 10V in “full open” position (to be clear, there are not just three stages; any voltage in-between 0V-10V puts the valve at that percentage of “openess”) We would like to be able to control the output in at least 1-2V increments to control the positioning of the valve.

Is there a way to use an Orangutan or Maestro or Qik/Jrk module to control an analog output signal as described above? Or do I need a digital POT IC? I’ve found this online maxim-ic.com/products/digi_pot/ but I’m not sure where to actually buy them, or which would be the most appropriate to use.

Any suggestions on how best to handle this kind of analog output would be greatly appreciated!

2

This site has a nice writeup:

dev.emcelettronica.com/how-to-us … its-part-2

3

Thanks for the info, but I don’t think the PWM method is most suitable for our application. We require a method more suitable to continuous changes in output voltage (the valve will move from close to partial-open and back to close on a regular cycle).

I guess the question comes down to whether there is an existing microcontroller or PIC board that offers variable voltage output, or if there is a simple secondary board or chip which can be digitally instructed to control a variable voltage output (e.g. a DAC or digital POT or something else I don’t know about!).

Let me provide some more detail on the application…

We begin with a simple pneumatic cylinder which is either extended or contracted, based on whether or not there is air pressure supplied. So this cylinder can be thought of as being “digital” in that it is either “on” (extended) or “off” (contracted).

The valve in question is attached between the air supply and the cylinder. Now, by supplying a variable voltage between 0V and 10V, the valve can control the air flow to the cylinder, thereby allowing it to be positioned at some point between extended and contracted. This can be thought of as converting the cylinder to “analog”.

Additional sensor(s) are the mounted to the cylinder and are able to measure the amount of extension. I do not believe the exact hardware has been chosen yet, but I think the sensor will provide 0-10V as an indication of the cylinder extension (proportionally opposite to the voltage going the valve). This input signal will need to be monitored and should bring high an output pin when and only when the measurement is at a predefined value.

Finally, two digital inputs are needed to allow input control of the system. The idea was to implement a simple clock/data protocol whereby one pin is held either high or low to indicate a desired increase or decrease in cylinder position, and a second pin is then toggled once per desired increment.

This would allow an existing, all-digital, PLC to utilize this enhanced valve control without having to completely redesign the existing PLC architecture. The PLC would toggle the clock pin on a regular period and would toggle the data pin whenever the input signal goes high (thus causing a reverse in the cylinder’s current direction which will pull the input low as soon as the extension leaves the target mark). This would allow for continuous movement of the cylinder within a range less than the normal maximum throw of the cylinder.

So that is what we are facing… The Maestro does everything perfectly, except for the variable voltage output. We really just need something like the Maestro, but with the required analog output, or something simple to attach to the Maestro which provides the required analog output under digital control by the Maestro.

Thanks!