Hardware Butterworth Filter
Due to the success we were having with
using the software Butterworth Filter, Tony decided to
design a hardware filter. This filter is used mainly on noisy or cluttered
signals like the data received from the Capacitor Sensor. The only downside of
using a hardware filter is it has a fixed filter setting and can’t be easily
changed. This filter works well, but once a recording is made, no practical adjustment of the filtered data can be done.
NASA and similar entities, have used software post-processing to extract useful data from noisy signals, for decades.
It is the most flexible approach.
Butterworth Filter circuit shown fitted to
the Capacitor Sensor
DOWNLOAD LARGER IMAGE (PDF)
Just below, is a recording of the output of the Hardware Butterworth Filter
and the Raw Capacitor sensor signal output from the circuit above. The Hardware Butterworth filter closely matches the Software Butterworth Filter
as can be seen in the images further below.
Software Butterworth Filter
By example here are the results with the
software Butterworth Filter using the same raw data but with different filter
settings.
Raw Data
0.05 Setting
0.005 Setting
0.0005 Setting, this setting is similar to
what we are getting with the hardware filter
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