# Mini Project Essay

2076 Words Oct 6th, 2015 9 Pages
EE2031 Circuit and Systems Design Lab

Mini-Project Report
Voice Disguiser
Presented by:
Friday Room 3 Group 7
Wang Ke (A0105276J)
Wu Jianxiao (A0099910W)

1.Introduction
1.1 Aim
During the 6 hands-on individual labs before this mini project, we have learnt the design and implementation of filter and oscillator, together with applied characterization of different components. The objective of Mini-Project was for students to demonstrate their innovative design skills and implement knowledge learnt in lectures to real-life product design. Therefore, we aimed to integrate what we learnt in individual labs into one single product, which is a Voice
Disguiser that can solve practical problems of witness protection.

1.2
The multiplication of the two signals allows modification of the voice frequency by changing the frequency of the square wave. The results are then amplified to a relatively larger scale for voice output.

2.3.1 Relaxation Oscillator
Figure 4 shows the circuit design of the relaxation oscillator used to produce the square wave. The time period of the output square wave is governed by the equation: T = 2CRln(3), where C = C1 = 1 uF, R = R3 (trimmer). The frequency can be found by f = 1/T, and is thus inversely proportional to the trimmer resistance value. The actual frequency-resistance relationship is shown in Figure 5, which presents the characterization results of the relaxation oscillator. From this characterization, we can see that the higher the resistance, the lower the frequency of oscillator square wave. Therefore, when we can control the frequency of this generated square waveform by adjusting the trimmer resistance. And the square wave is then used as a frequency carrier for the voice signals.

R/ohms

Frequency vs. Resistor Value Graph (Relaxa9on Oscillator)

200 180 160 140 120 100 80 60 40 20 0

F/Hz
0

Figure 4: Schematic of Oscillator

2000

4000

6000

8000

10000

12000

Figure 5:

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