Week 1

The apparatuses in this project were collected successfully. In this week, the aim of our group is to assemble the microphone amplify circuit and code Arduino program to test it. We firstly measured the voltage range of the microphone without amplified. The range finally we measured through oscilloscope is around -190 mV to 200 mV. The voltage range of the Arduino board analogue in point is 0 to 5 volt. Thus the amplifier circuit need to amplifier the sound signal from ±200 mV to ±2 V and then set the voltage offset 2 volt. In this circuit, we use the operational amplifier to built the amplify circuit. The operational amplifier was shown in Figure 1. 

The voltage gain of the operational amplifier could be shown:

Figure 1. Operational amplifier

For operational amplifier analysis, two terminal of the amplifier have the same voltage. Thus the voltage could be shown:

As a result, the amplify circuit could be seen in Figure 2 and Figure 3.

Figure 2.  Amplifier circuit diagram

Figure 3. Amplifier circuit

According to the circuit diagram, point A (9 volt) worked as the ground for the whole system. So point B (0 volt) could provide -9 volt for op amp. Resistors C and D were combined together to adjust the amplification. D was the feedback resistor. Capacitor E is to prevent the DC signal from the right part of the circuit. While F is the bypass capacitor. Resistors G and H were combined together to form the voltage bias circuit as the Arduino only receive the analog signal with range 0 to 5 volt. In above circuit, the function generator represents the input signal of the microphone.

Finally, to tested the circuit, we wrote a Arduino program that the Arduino board would put the digital data of the analogue signal to the serial port. Then through serial port tool:

Figure 4. Serial port display

Summary: The work of this week implemented smoothly. In next week, we will contribute to the circuit modification and Arduino board to computer communication.