erkin yucel / mbed-os

mbed os with nrf51 internal bandgap enabled to read battery level

Dependents:   BLE_file_test BLE_Blink ExternalEncoder

tools/dev/dsp_fir.py@0:f269e3021894, 2016-10-23 (annotated)

Committer:
elessair
Date:
Sun Oct 23 15:10:02 2016 +0000
Revision:
0:f269e3021894
Initial commit

Who changed what in which revision?

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elessair 0:f269e3021894 1 """
elessair 0:f269e3021894 2 mbed SDK
elessair 0:f269e3021894 3 Copyright (c) 2011-2013 ARM Limited
elessair 0:f269e3021894 4
elessair 0:f269e3021894 5 Licensed under the Apache License, Version 2.0 (the "License");
elessair 0:f269e3021894 6 you may not use this file except in compliance with the License.
elessair 0:f269e3021894 7 You may obtain a copy of the License at
elessair 0:f269e3021894 8
elessair 0:f269e3021894 9 http://www.apache.org/licenses/LICENSE-2.0
elessair 0:f269e3021894 10
elessair 0:f269e3021894 11 Unless required by applicable law or agreed to in writing, software
elessair 0:f269e3021894 12 distributed under the License is distributed on an "AS IS" BASIS,
elessair 0:f269e3021894 13 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
elessair 0:f269e3021894 14 See the License for the specific language governing permissions and
elessair 0:f269e3021894 15 limitations under the License.
elessair 0:f269e3021894 16 """
elessair 0:f269e3021894 17 from numpy import sin, arange, pi
elessair 0:f269e3021894 18 from scipy.signal import lfilter, firwin
elessair 0:f269e3021894 19 from pylab import figure, plot, grid, show
elessair 0:f269e3021894 20
elessair 0:f269e3021894 21 #------------------------------------------------
elessair 0:f269e3021894 22 # Create a signal for demonstration.
elessair 0:f269e3021894 23 #------------------------------------------------
elessair 0:f269e3021894 24 # 320 samples of (1000Hz + 15000 Hz) at 48 kHz
elessair 0:f269e3021894 25 sample_rate = 48000.
elessair 0:f269e3021894 26 nsamples = 320
elessair 0:f269e3021894 27
elessair 0:f269e3021894 28 F_1KHz = 1000.
elessair 0:f269e3021894 29 A_1KHz = 1.0
elessair 0:f269e3021894 30
elessair 0:f269e3021894 31 F_15KHz = 15000.
elessair 0:f269e3021894 32 A_15KHz = 0.5
elessair 0:f269e3021894 33
elessair 0:f269e3021894 34 t = arange(nsamples) / sample_rate
elessair 0:f269e3021894 35 signal = A_1KHz * sin(2*pi*F_1KHz*t) + A_15KHz*sin(2*pi*F_15KHz*t)
elessair 0:f269e3021894 36
elessair 0:f269e3021894 37 #------------------------------------------------
elessair 0:f269e3021894 38 # Create a FIR filter and apply it to signal.
elessair 0:f269e3021894 39 #------------------------------------------------
elessair 0:f269e3021894 40 # The Nyquist rate of the signal.
elessair 0:f269e3021894 41 nyq_rate = sample_rate / 2.
elessair 0:f269e3021894 42
elessair 0:f269e3021894 43 # The cutoff frequency of the filter: 6KHz
elessair 0:f269e3021894 44 cutoff_hz = 6000.0
elessair 0:f269e3021894 45
elessair 0:f269e3021894 46 # Length of the filter (number of coefficients, i.e. the filter order + 1)
elessair 0:f269e3021894 47 numtaps = 29
elessair 0:f269e3021894 48
elessair 0:f269e3021894 49 # Use firwin to create a lowpass FIR filter
elessair 0:f269e3021894 50 fir_coeff = firwin(numtaps, cutoff_hz/nyq_rate)
elessair 0:f269e3021894 51
elessair 0:f269e3021894 52 # Use lfilter to filter the signal with the FIR filter
elessair 0:f269e3021894 53 filtered_signal = lfilter(fir_coeff, 1.0, signal)
elessair 0:f269e3021894 54
elessair 0:f269e3021894 55 #------------------------------------------------
elessair 0:f269e3021894 56 # Plot the original and filtered signals.
elessair 0:f269e3021894 57 #------------------------------------------------
elessair 0:f269e3021894 58
elessair 0:f269e3021894 59 # The first N-1 samples are "corrupted" by the initial conditions
elessair 0:f269e3021894 60 warmup = numtaps - 1
elessair 0:f269e3021894 61
elessair 0:f269e3021894 62 # The phase delay of the filtered signal
elessair 0:f269e3021894 63 delay = (warmup / 2) / sample_rate
elessair 0:f269e3021894 64
elessair 0:f269e3021894 65 figure(1)
elessair 0:f269e3021894 66 # Plot the original signal
elessair 0:f269e3021894 67 plot(t, signal)
elessair 0:f269e3021894 68
elessair 0:f269e3021894 69 # Plot the filtered signal, shifted to compensate for the phase delay
elessair 0:f269e3021894 70 plot(t-delay, filtered_signal, 'r-')
elessair 0:f269e3021894 71
elessair 0:f269e3021894 72 # Plot just the "good" part of the filtered signal. The first N-1
elessair 0:f269e3021894 73 # samples are "corrupted" by the initial conditions.
elessair 0:f269e3021894 74 plot(t[warmup:]-delay, filtered_signal[warmup:], 'g', linewidth=4)
elessair 0:f269e3021894 75
elessair 0:f269e3021894 76 grid(True)
elessair 0:f269e3021894 77
elessair 0:f269e3021894 78 show()
elessair 0:f269e3021894 79
elessair 0:f269e3021894 80 #------------------------------------------------
elessair 0:f269e3021894 81 # Print values
elessair 0:f269e3021894 82 #------------------------------------------------
elessair 0:f269e3021894 83 def print_values(label, values):
elessair 0:f269e3021894 84 var = "float32_t %s[%d]" % (label, len(values))
elessair 0:f269e3021894 85 print "%-30s = {%s}" % (var, ', '.join(["%+.10f" % x for x in values]))
elessair 0:f269e3021894 86
elessair 0:f269e3021894 87 print_values('signal', signal)
elessair 0:f269e3021894 88 print_values('fir_coeff', fir_coeff)
elessair 0:f269e3021894 89 print_values('filtered_signal', filtered_signal)