14th FEB - The Third Lab - Modify Actual Circuit & Test

Last week, we didn't get any signal from the output terminal, which upsets us a lot. this week, we used one entire morning on the actual circuit. this time, we changed our strategy, we build the circuit in the sequence of its function and tested it one by one. The final circuit in figure 1. The first two operational amplifiers are used to amplify the signal, the third operational amplifier is used to turn analog signal into binary form, the fourth operational amplifier is used as compactor. 

figure 1

The reaction of our first stage operational amplifier is shown in the video below, it can be seen that when a palm is swept above, there is a signal from its terminal, the output is too tiny to be used, and the reason is about the gain of this amplifier, which can be changed by the variable resistor.
video of stage 1:

the reaction of the second stage operational amplifier is shown in the video, it can be seen that its reaction towards a sweeping palm is larger in amplitude compared to the first stage amplifier.
video of stage 2:

the reaction of the third stage operational amplifier is shown in the video below, it converts the analog signal to digital signal, it can be seen from the video that when a palm sweep out, there is a '1' in the output, otherwise it is '0'. moreover, the output signal is also related to the velocity of the sweeping palm, it a palm swept quicker, there is more '1' in output with shorter time period.
video of stage 3: 

the reaction of fourth amplifier is a DC voltage about 2-3 V, and its function is to stablize the system and make the output signal more smooth.
the video below shows the result when a LED is connected to the output of third stage, it proves to be sensitive and stable.
After this, we began to do some test about the sensor's working range, the result is that , at about two meters away, and within the range of 60 degrees, the sensor can detects people's motion sensitively. And this result is really satisfying.
next week, we will build another PIR sensor circuit, and calibrate the two circuit with same amplification effect and response time, and put them vertically so that we can detect the motion of fall, hopefully we can finish our job next week.