[SciPy-User] Low pass filter

[Kaan AKŞİT]

Thanks Ivo, The problem is after filtering I got the same signal. I wanted
to clear the frequencies higher then 5 Hz. My code is similar to yours but
the output doesn't seem logical:

#!/usr/bin/python
# -*- coding: utf-8 -*-
import time, array, datetime
import matplotlib
import matplotlib.pyplot as plt
from scipy import *
from scipy.signal import butter, lfilter

input = 0
timing = []
voltage  = []
values = []

input = 0
infile = open('measurements/' + "data.csv", "r")
for line in infile.readlines():
    values = line.split(',')
    voltage.insert(input,float(values[0]))
    timing.insert(input,float(values[1]))
    input = input + 1
plt.xlabel('Time steps')
plt.ylabel('Voltage')
plt.title('Measurments from Oscilloscope')
plt.grid(True)
plt.plot(voltage,timing)
[b,a]=butter(2,5)
voltagelowp=lfilter(b,a,voltage)
plt.plot(voltagelowp,timing)
plt.show()
plt.close()

2009/9/17 Ivo Maljevic <ivo.maljevic at gmail.com>

> Does the following:
>
> plt.plot(timing, voltage)
> plt.show()
>
> work before filtering? (Suggestion, you may want to put time on x-axis, see
> the line above)
>
> I just wrote a small test program, and it works:
>
>
> #!/usr/bin/python
>
> # import
> import pylab as plt
> from scipy import *
> from scipy.signal import butter, lfilter
>
> t=linspace(0,1,100)
> v=sin(2*pi*t)
>
> (b,a)=butter(2,5,btype='low')
> v=lfilter(b,a,v)
> plt.plot(t,v)
> plt.show()
>
>
> 2009/9/17 Kaan AKŞİT <kunguz at gmail.com>
>
>> Hi all,
>>
>> This is my first time that I use Scipy. I have two arrays both of them one
>> dimensional. One of them is filled with voltage values and one of them is
>> filled with time values. I want to apply low pass filter to clear the noise
>> from the data. Can you please help me? I already wrote something but it is
>> not working:
>>
>> (b,a)=butter(2,5,btype='low')
>> voltage=lfilter(b,a,voltage)
>> plt.plot(voltage,timing)
>>
>> Best regards,
>> Kaan
>>
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>>
>>
>
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