# Mini Project

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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…show more content…
Figure 1: Project Flowchart 2.2 Microphone Unit The microphone was implemented to allow the user to transmit speaker’s voice as analog voice signal from the audio socket. The analog voice signal captured by the microphone is then needed to pass through an amplifier circuit. The amplitude of this voice signal can be amplified from millivolts to volts so that the signal becomes easier to for us work with in following implementations. As figure 2 shown, this amplifier circuit is built by firstly connecting the microphone input through the positive input terminal of the LM358 chip. Secondly, a feedback loop is built through the output and negative terminal. Then the analog voice signal captured by the microphone is, therefore, amplified. Figure 2: Schematic Of Microphone Unit The resistance values of R4 and R3 is purposely chosen for an amplifier gain of 5.7. As shown in Figure 3, a significant amplifying effect of the microphone voice signal can been seem afer passing through the amplifier. Figure 3: Waveform Of Voice Signal Before (Blue) And After (Yellow) Amplifier Based on oscilloscope detection, the peak-to-peak value of microphone voice signal before amplifier is 220mV, while the one after the amplifier is 1.28V. The actual amplifier gain is therefore 5.8 (1.28/0.22), which is very close to the designed value of 5.7. 2.3 Frequency Modification Unit This