[chbot] Filter

[mikael stewart]

You could use a simple IIR filter that weights the most recent input by say
1/100th:

filt_value = (filtered_value * 99 + raw_value) / 100;

If filt_value is floating point and the calculation is done in an
approximately constant loop interval this works well.

This can also be done with integers noting the result of "(filtered_value *
99) + raw_value" should not exceed the size of the integer.

The quantization is not so nice in the above method though because it gets
multiplied by the * 99. A better way might be to keep track of a running
sum with one variable, and use a second variable for the filtered result:

filt_sum = filt_sum - filt_sum / 100 + raw_value;
filt_value = filt_sum / 100;

The second line only needs to be evaluated when you actually need to use
the result.

Cheers

Mikael


On Thu, Oct 18, 2018 at 9:06 AM Marshland Engineering <
marshland at marshland.co.nz> wrote:

> I need to do some software filtering. I'm reading a camshaft with a 0.001
> linear scale and there is quite a bit of noise in the data. Looking on the
> web
> has left me non the wiser. Rectangular or Triangle filters are an option
> but
> these will loose some data integrity. The profile is a very gentle curve
> with
> the data around the ctr line.
>
> I hoping for something simple !!!!
>
> Thanks Wallace.
>
>
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