Week 2 Activities

This is the second week of this project and the components we ordered were all arrived. 

The circuits were done for the first time for both receivers and transmitters which spent the half day. However, the circuit of the receiver was tested at first. 

LM376 is an op amp chip, which totally has eight pins. Pin 1 and Pin 8 are GAINs, which control the gain of this amplifier. When Pin 1 and Pin8 are disconnected, the gain of the receiver circuit is 20. However, we want to achieve the gain as large as possible, so a capacitor was used to achieve the maximum gain 200. 

Pin 2 and Pin 3 are -INPUT and +INPUT. The Pin 2 is connected with the ground and Pin 3 is an input terminal. An output capacitor is also connected between the antenna and earphone, which is considered as coupling capacitor to reduce the noise. Pin 4 is GND, which is connected to the ground. Pin 5 is OUTPUT. Moreover, Pin 6 is linked with positive terminal of the voltage. 

Additionally, Pin 7 is BYPASS, between the ground and Pin 7, there is a shunt capacitor to filter the high frequency. 

The original design of the receiver is shown below. 

After the test, we could hear some noise in the earphone, but no sound or program. Thus, we found that the adjustment of the frequency is pretty necessary; in order to find an appropriate frequency that the receiver can receiver the signal. 

There are three main changes of the design. A variable capacitor and a inductor in parallel  are connected between the input signal (i.e. antenna)and the ground to achieve the adjustment of the frequency. Besides, we add a variable resistor to adjust the gain of the signal in order to adjust the volume(i.e. change the gain of the circuit). 

Moreover, some values of the components were also changed to achieve better resulting test. In addition, a 10Ω resistor is series with a 0.1μF capacitor is connected with Pin 5 to make the circuit more stable.

The updated design is indicated in the figure below.

Because the time was limited during the Friday, so that there is no enough time for us to test the new circuit. 

After that, the circuit for transmitter is also changed for better design, but some problems are found and needed to be solved.

It is unfortunate for us to make no progress of the real circuit this week. Therefore, what we can do is to check the updated designs and use PSpice to simulate the circuit to ensure the circuit can work effectively and normally.