Week 4

Week 4 Finish building the PIR circuit and package.

Last week, we have finished the first amplifier of the PIR circuit, and this week, we built the second amplifier and comparator which is shown in Figure 1.
Figure 1 (PIR sensor circuit)

Meanwhile, we connected a LED light to the output of the comparator. When nobody moves in front of the PIR sensor, the light will be turned on, and when the human motion is detected the LED will flash which is shown in the video. We infer that when no one passes through the PIR sensor, there is always a DC signal in the circuit because we used a power supply to supply DC voltage to the amplifier. The reason for this phenomenon is that the final part is Op-amp Comparator, which is used to digitalize the signal, and we choose the non-inverter comparator circuit. When there is no input signal, the output signal is the reference voltage, if there is an input signal which is similar to a sinewave, which makes the output signal up and down like a square wave. This will make LED light flash. In order to ensure the LED light flash, R9=R8, and R11=R12, which means we should add a 2.5 V DC signal in amplifier 2 because the reference voltage of the comparator is 2.5 V.


Figure 2 The PIR sensor circuit



Finally, we package our circuit. We use the box to build a small house and stick the circuit on the top of the house, and connect the PIR sensor to the house.
               
Figure2 The automatic door




Figure 3 Final circuit



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