Week 4 Activities

It is week 4 now, which is very close to the end of the project.

Last week we reconstructed and improve the circuits for the receiver and transmitter. So this week, we tested the receiver and transmitter at the same time. The receiver still has problems. However, the transmitter seemed to be working.

As a consequence, in this week, our group concentrated on the transmitter for the simulated design. MP3 was connected into the circuit as the input signal. Fortunately, the transmitter circuit was working, we can hear the input sound from the AM radio; however, there was some noise when listening to the AM radio.

Therefore, we considered to change some resistors (increase R4 and R6 and reduce R2 )to reduce the gain of the transistor, which might reduce the noise. However, the values for resistors were not correct, so that it was not effective.

After that, the resistors were changed back to original ones. What was unfortunate was that the circuit did not work anymore. We wanted to check out whether the output is available measured by using oscilloscope and the result came out with zero output.

Then, we thought that the components of the circuit must be damaged, especially capacitors.

In order to simplify the circuit, the changes of each LC tank circuit are that the inductor L1 was changed to approximately 540μH for 60 turns and the variable capacitor in transmitter was changed to a fixed-value capacitor 100pF.

According to the frequency equation for LC tank circuit, f=1/(2π×√LC)≈680kHz, which is in the range of AM radio.

A can is used for antenna. The real transmitter circuit was built and shown below:

However, at the end of the week 4, we still failure to make progress of the transmitter for the circuit not working. Nevertheless, the circuit was working before and the simulation demonstrates the design   should have no errors. Therefore, there might be something ignored that affects the circuit.

As a consequence, the next week is the last time for us to conduct the project, the transmitter should be done well. I think there is few time for us to complete the receiver; however, we will try efforts to do as much as possible for the receiver.