In this week, we improve the circuit on the breadboard and the code of the Arduino equipment. In the past circuit, when we measure the wave of the output of the circuit, we discover it exists so much wave we don't need like figure1

figure1

we decide to use a filter to decrease the noise and the wave we don't need. We use a  capacitance as a filter in parallel with the circuit like figure 2. 

figure2

Firstly we choose a capacitance resistance 390Ω capacitance be the filter. We could get a figure 3 of the output.

figure3

Then we choose a 680Ω capacitance be the filter we get a wave picture like figure 4

figure4

Then we choose a 1kΩ capacitance be the filter we get a wave picture like figure 5 

figure5

By the observation could discover that when the resistance of the capacitance become bigger that the noise and the wave we don't need is decreased . 

Apart from the activities the above, we change the message in the code that " HelloWorld" to another word. And we discover that quantity of the letter of the another word should be equal with the initial word that "HelloWorld.