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'******************************************************************************
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'* ChirpGenerator *
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'* *
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'* This class implements a custom control to generate a chirp signal *
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'* The user can modify the frequency,output power and decay in real time. *
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'* *
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'* We calculate the minimum samples of the tone that we need to generate a *
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'* continous signal with the given sampling and output frequency. *
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'* Then, each time the caller want to have a new fragment of the signal, we *
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'* repeat the calculated samples as many times as we need to fill the output *
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'* buffer. *
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'* *
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'* EQUITEL - C.V. February 2007 ALMDI *
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'******************************************************************************
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Imports System.ComponentModel
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Imports System.Math
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Public Class ChirpGenerator
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Private mInternalBuffer As Short()
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Private mBufSize As Integer
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Private mSamplingFrequency As Integer = 8000
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Private mFrequency As Integer = 1000
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Private mPower As Double = -0
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Private mSignalIsGenerated As Boolean = False
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Private mDecayTime As Integer
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Private mPeriodSamples As Integer = 160
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#Region "Propiedades"
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<Category("Signal"), DefaultValue(GetType(Integer), "8000"), _
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Description("Sampling frequency of the desired signal")> _
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Public Property SamplingFrequency() As Integer
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Get
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Return mSamplingFrequency
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End Get
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Set(ByVal value As Integer)
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If value >= 8000 AndAlso value <= 96000 Then
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mSamplingFrequency = value
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End If
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End Set
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End Property
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<Category("Signal"), DefaultValue(GetType(Integer), "1000"), _
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Description("Frequency of the desired signal")> _
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Public Property Frequency() As Integer
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Get
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Return mFrequency
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End Get
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Set(ByVal value As Integer)
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If value >= 100 AndAlso value <= mSamplingFrequency / 2 Then
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mFrequency = value
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CtrlFrequency.Value = value
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lblFrequency.Text = Format(mFrequency / 1000, "0.0 kHz")
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CalculateSignal()
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End If
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End Set
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End Property
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<Category("Signal"), DefaultValue(GetType(Integer), "-100"), _
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Description("Relative output level of the signal in decibels")> _
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Public Property Power() As Double
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Get
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Return mPower
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End Get
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Set(ByVal value As Double)
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If value >= -100 AndAlso value <= 0 Then
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mPower = value
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CtrlPower.Value = value
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lblPower.Text = Format(value, "0 dB")
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CalculateSignal()
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End If
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End Set
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End Property
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<Category("Signal"), DefaultValue(GetType(Integer), "10"), _
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Description("Time the signal takes to fall to the 10% of amplitude (in ms)")> _
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Public Property T_Decay() As Double
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Get
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If mDecayTime < 1 Then mDecayTime = 1
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Return mDecayTime
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End Get
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Set(ByVal value As Double)
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If value <= 100 AndAlso value > 1 Then
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mDecayTime = value
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CtrlDecay.Value = value
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LblDecay.Text = Format(value, "000 ms")
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CalculateSignal()
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End If
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End Set
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End Property
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<Category("Signal"), DefaultValue(GetType(Integer), "20"), _
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Description("Period of the Chirp (in ms)")> _
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Public Property ChirpPeriod() As Integer
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Get
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Return (mPeriodSamples * 1000) / mSamplingFrequency
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End Get
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Set(ByVal value As Integer)
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If value <= 1000 AndAlso value > 1 Then
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mPeriodSamples = value * (mSamplingFrequency / 1000)
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LblPeriod.Text = Format(value, "000 ms")
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CalculateSignal()
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End If
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End Set
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End Property
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#End Region
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Private Sub CalculateSignal()
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Dim i As Integer
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Dim t As Double
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Dim W As Double
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Dim Factor As Double
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Dim Vmax As Integer
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ReDim mInternalBuffer(mPeriodSamples - 1)
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mBufSize = mPeriodSamples
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W = 2 * 3.141592659 * mFrequency
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Factor = 20 ^ (mPower / (10 * 3))
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Vmax = Int(32767 * Factor)
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For i = 0 To mPeriodSamples - 1
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t = i * (1 / mSamplingFrequency)
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Try
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mInternalBuffer(i) = Vmax * Sin(W * t) * Exp(-t / (T_Decay / 2302))
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Catch e As Exception
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MsgBox("Chirp signal generation error", MsgBoxStyle.Critical)
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End Try
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Next
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mSignalIsGenerated = True
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End Sub
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Private Sub Power_Scroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CtrlPower.Scroll
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Power = CtrlPower.Value
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End Sub
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Private Sub Frequency_Scroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CtrlFrequency.Scroll
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CtrlFrequency.Value = Int(CtrlFrequency.Value / 100) * 100
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Frequency = CtrlFrequency.Value
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End Sub
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Private Sub CtrlDecay_Scroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CtrlDecay.Scroll
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T_Decay = CtrlDecay.Value
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End Sub
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Private Sub CtrlPeriod_Scroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CtrlPeriod.Scroll
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ChirpPeriod = CtrlPeriod.Value
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End Sub
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Public Sub OutputPacket(ByRef Buffer As Short(), ByVal NumSamples As Integer)
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Dim i As Integer
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Static mInternalBufferPointer As Integer = 0
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If Not mSignalIsGenerated Then CalculateSignal()
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For i = 0 To NumSamples - 1
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Buffer(i) = mInternalBuffer(mInternalBufferPointer)
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mInternalBufferPointer += 1
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If mInternalBufferPointer = mBufSize Then
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mInternalBufferPointer = 0
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End If
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Next
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End Sub
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End Class
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