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View Full Version : LabVIEW Filter help needed

Ivan Helmrich
09-02-2009, 14:50
I want to put a low pass filter on the joystick axes to limit accelleration. I've found a low pass filter vi (equi-ripple lawpass filter.vi) that I think should work but I'm not sure what to do with it. When I try to wire the joystick to the filter, it tells me that I have a scalar going into an array of that type. I guess I don't understand what I need to do with the joystick value to get it into an array that is useful. For that matter, I don't really know what the array should consist of.

Short term of course, I'm just looking for a solution. Long term, I'd really like to have an understanding of what needs to go in the filter. I'm not a controls guy so I'm a little confused by the taps also. Is there is a simpler filter I should use?

Anybody got the time to post a screenshot of how to hook this up or an explanation of how to make this work? I'm trying to do this in the teleop vi of the Advanced Project. Thanks.
EricVanWyk
09-02-2009, 15:11
I wrote a small intro to this, but didn't have the time to go into full detail - http://thinktank.wpi.edu/article/140. If you can, please update it to include your findings.

Your scalar/vector problem indicates that you need to use the Pt by Pt version of the filter. One version just grabs a whole mess of data at once and filters it. The Pt by Pt version grabs it one point at a time and gives an output one point at a time.
Ivan Helmrich
09-02-2009, 15:43
Eric,

Thanks, that helps a lot. This gives me a couple of ideas to try tonight.

Ivan
Greg McKaskle
09-02-2009, 20:19
If you add analysis to your VIs, you will want to open the deployment build specification, go to the Additional Exclusions tab and Check the box to remove library VIs that aren't needed. This is a workaround that will otherwise slow your build and deploy way down.

And as you already found out, use one of the pt by pt filter VIs and you are in good shape.

Greg McKaskle
Ivan Helmrich
10-02-2009, 13:37
OK, I've got something that I think will work. If I get the time to experiment, I'll be looking to increase the level of awesomeness before ship! Thank you both.

Ivan