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delene Guest
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filtering load cells |
Posted: Wed Jul 09, 2003 2:58 am |
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I have used the PIC18f452 to design a scale - it works great for small scale and weighbridges.
I know want to modify it to weigh cattle.
My problem is that the cattle jumps about - there is never a stable ready. What I want to do is lock the display on the mass of the scale. ie. If you weigh 60kg and jump on the scale after a couple of seconds the scale must lock on 60kg as your weight.
Does anyone have any idea how I go about this.
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Original Post ID: 144515804 |
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Kenny
Joined: 07 Sep 2003 Posts: 173 Location: Australia
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Re: filtering load cells |
Posted: Wed Jul 09, 2003 4:10 am |
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:=I have used the PIC18f452 to design a scale - it works great for small scale and weighbridges.
:=I know want to modify it to weigh cattle.
:=My problem is that the cattle jumps about - there is never a stable ready. What I want to do is lock the display on the mass of the scale. ie. If you weigh 60kg and jump on the scale after a couple of seconds the scale must lock on 60kg as your weight.
:=
:=Does anyone have any idea how I go about this.
A very effective method posted by Mr. Hamlett that I have used in similar situations:
<a href="http://www.pic-c.com/forum/general/posts/8286.html" TARGET="_blank">http://www.pic-c.com/forum/general/posts/8286.html</a>
There are others posted on this forum, place 'filter' in the search.
Regards
Kenny
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Original Post ID: 144515808 |
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delene Guest
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Re: filtering load cells |
Posted: Wed Jul 09, 2003 4:55 am |
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Thanks Kenny
I will give it a try and let you know
Delene
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Original Post ID: 144515813 |
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R.J.Hamlett Guest
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Re: filtering load cells |
Posted: Wed Jul 09, 2003 5:29 am |
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:=Thanks Kenny
:=I will give it a try and let you know
:=
:=Delene
I would suggest, that you might need to add a bit of 'intelligence' to the filtering as well. For instance, if you know that the maximum weight that should ever be seen, is a particular value, you could reject any figure above this value (corresponding to a sudden force as an animal jumps), before feeding the numbers into the filter algorithm. You could then have the damping 'assymetric', so that it responds slower to a loss of weight, than to a weight being added, which shouldn't then result in a tendency to 'overweigh' (which would otherwise happen with such an assymetric response. Tuning the algorithm, would be easiest, by having variables holding values for 'upsmall', 'uplarge', 'downsmall', 'downlarge' (corresponding to the points where you change the slope of the damping), and for 'max', 'smalldiv', 'largediv', (the division ratios to be used). If you allow these to be updated externally, using a serial link, you can experiment, to actually see how to get the damping to work best for you. The particular problem you are going to have, is that the 'jump' upwards in value, when an animal steps onto the platform, will be very similar to the jump seen when the animal moves. I would possibly think in terms of turning the damping down, when the platform receives a small duration of signal close to zero (a couple of successive samples), then accepting the first 'high' figure after this (as the animal first jumps on), and then damping more massively from this.
If you have access to a data logger (or could put together some code to do this with the PIC), you might consider getting some typical 'snapshot' raw data sequences, and trying different levels of damping on these in the PC, to see what the best solution is.
Best Wishes
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This message was ported from CCS's old forum
Original Post ID: 144515814 |
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PCM programmer
Joined: 06 Sep 2003 Posts: 21708
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Re: filtering load cells |
Posted: Wed Jul 09, 2003 12:41 pm |
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:=I have used the PIC18f452 to design a scale - it works great for small scale and weighbridges.
:=I know want to modify it to weigh cattle.
:=My problem is that the cattle jumps about - there is never a stable ready. What I want to do is lock the display on the mass of the scale. ie. If you weigh 60kg and jump on the scale after a couple of seconds the scale must lock on 60kg as your weight.
:=
:=Does anyone have any idea how I go about this.
----------------------------------------------------
Collect some sample data, and import (or type) it into Excel.
Use the built-in statistical functions, such as AVERAGE or
MEDIAN, etc. to test different filters. You can test other
filters by typing in an equation. Excel can also graph the
results. This is how I proved to myself that a median
filter would work best for my project. A median filter
removes "spikes" from data.
<a href="http://www.pic-c.com/forum/general/posts/13211.html" TARGET="_blank">http://www.pic-c.com/forum/general/posts/13211.html</a>
You can use Excel to model the filter, and test it against
real data. You can see exactly how your PIC program will work,
in advance. And you don't have to buy MatLab. Most people
already have Excel on their PC.
I think the most important thing is to bring the data into
Excel, make a graph of it, and study it. Then you can
decide what filter (or filters) you need.
For lots of discussion articles on using filters with PICs,
go here: <a href="http://groups.google.com/advanced_group_search" TARGET="_blank">http://groups.google.com/advanced_group_search</a>
Set the group for comp.arch.embedded.piclist" and do a search
for: filter
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This message was ported from CCS's old forum
Original Post ID: 144515824 |
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C Shah
Joined: 16 Jun 2006 Posts: 1 Location: INDIA
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Re: filtering load cells |
Posted: Fri Jun 16, 2006 8:08 am |
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[quote="delene"]I have used the PIC18f452 to design a scale - it works great for small scale and weighbridges.
I know want to modify it to weigh cattle.
My problem is that the cattle jumps about - there is never a stable ready. What I want to do is lock the display on the mass of the scale. ie. If you weigh 60kg and jump on the scale after a couple of seconds the scale must lock on 60kg as your weight.
Does anyone have any idea how I go about this.
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515804[/quote]
I would like to get atleast 18bits of stable ADC data (from 24bit CS5532) connected to loadcell. Also, it should reject all vibrations, other sudden/temporary effects like overhead fan blowing air on it etc... Can anyone help me out on the issue? CPU used in 8051 based core (plenty of ROM+RAM available)!
Thnx
C Shah |
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Ttelmah Guest
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Posted: Fri Jun 16, 2006 10:39 am |
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If it is an '8051 core', then go and ask on a group for this. This group is for people usng _CCS C_, on the PIC processor.
Best Wishes |
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Shah Guest
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Filtering Loadcells |
Posted: Mon Jun 19, 2006 8:06 am |
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Ttelmah wrote: | If it is an '8051 core', then go and ask on a group for this. This group is for people usng _CCS C_, on the PIC processor.
Best Wishes |
Thanks - But as I wish algorithm / hint on "HOW TO" go about solving the problem - hence PIC / '51 core is not very important... I still await positive response on the issue...
Regards
C Shah |
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SherpaDoug
Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA
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Posted: Mon Jun 19, 2006 8:14 am |
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I want to second the idea that you log some data to a PC and play with it using a spreadsheet or other good math modeling tools. Once you figure out what works you can then figure out how to do it in a microprocessor. It is probably going to be more than just averagings. Try googling "Median Filter" or searching for "olymipc scoring" on this forum. _________________ The search for better is endless. Instead simply find very good and get the job done. |
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Ttelmah Guest
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Re: Filtering Loadcells |
Posted: Mon Jun 19, 2006 9:03 am |
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Shah wrote: | Ttelmah wrote: | If it is an '8051 core', then go and ask on a group for this. This group is for people usng _CCS C_, on the PIC processor.
Best Wishes |
Thanks - But as I wish algorithm / hint on "HOW TO" go about solving the problem - hence PIC / '51 core is not very important... I still await positive response on the issue...
Regards
C Shah |
The same comment still applies. This is a group for people having _CCS_ problems, _not_ a general arithmetic group. Filtering algorithms are as common as muck, and 5 minutes with google will point you to places covering these. If you have bought a CCS compiler, and have a CCS specific problem with how to implement a filter, then post here, otherwise 'go away'.
As a general hint, if you want to look through the archive here, do a search for 'olympic sorting'. A similar search on normal filtering will find a number of general algorithms. The combination, of a rolling average algorithm, with an olympic sorting algortithm, is the sort of approach that will be needed for this problem.
Best Wishes |
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