20/2/2012 Week 4

Because the value of the output in the primary circuit was small, we decided to build a second-class amplifying circuit as primary circuit. 

Then the modified circuit is drawn by Pspice as below,

The output of the second-class amplifying circuit has too much noise,

We considered the reasons of the condition,

1.bad contact

2.high- frequency oscillation

For the first idea, we checked all components and contacts, the output wave had no change. As a result, this condition is eliminated.

In order to solve the problem of high- frequency oscillation, we decided to add a capacitor to the second-class circuit as shown in figure below. We have tried many different values of the capacitors, and finally 68n is considered to be proper. 

The values of R8 and R9 are changed to 27k and 18k, 

Finally, when hands shaking in front of the PIR sensor, the output of the third part is shown as below