import math
import matplotlib.pyplot as plt

Fs = 10000 # samples per second

phase = 0

time = []
signal = []

for i in range(10000):

    if i < 5000:
        f = 100   # frequency
    else:
        f = 200   # frequency

    phase += 2 * math.pi * f / Fs
    #sample = math.cos(phase)
    sample = math.sin(phase)
    
    time.append(i / Fs)
    signal.append(sample)

plt.plot(time, signal)
plt.xlabel("Time (seconds)")
plt.ylabel("Amplitude")
plt.title("Cosine Wave")
plt.grid()
plt.show()