import numpy as nupy
import matplotlib.pyplot as plt

f1 = 1 # starting frequency in Hz
f2 = 5 # final  frequency in Hz
np = 1000. # number of points
dt = 0.01 # time step

idx = nupy.arange(np)/(np - 1.)
ts = idx*np*dt
freqs = (f2 - f1)*idx + f1
phi = nupy.cumsum(freqs*dt)
sig = nupy.sin(2.*nupy.pi*phi)
sigfft = nupy.fft.fft(sig)
amp = (nupy.abs(2*sigfft/np))[0:np/2+1]
pha = (nupy.angle(sigfft))[0:np/2+1]
freq = nupy.arange(np/2 + 1)/(np*dt)

plt.figure()

plt.subplot(2, 1, 1)
plt.plot(ts, sig)
plt.xlabel("Time [s]")
plt.ylabel("Amplitude")

plt.subplot(2, 1, 2)
plt.plot(freq, amp)
plt.xlabel("Frequency [Hz]")
plt.ylabel("Amplitude")

plt.show()