Instructables
Picture of Use a Motion Sensor to Automate Your Haunted House
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One of the most useful sensors for automating a haunted house is a motion sensor. This sensor lets you activate your special effects only when a new group of people arrives. That way the surprise won't be ruined by people seeing or hearing the effects before they get close enough.

In this project, I am going to show you several ways that you can use a motion sensor to automate your Halloween setup.
 
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Step 1: How Passive Infrared (PIR) Motion Sensors Work

Picture of How Passive Infrared (PIR) Motion Sensors Work
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For a good in-depth tutorial of all things related to PIR motion sensors you can check out this page by adafruit: 
http://www.ladyada.net/learn/sensors/pir.html
I will attempt to give a brief summary here.

Passive Infrared (PIR) motion sensors work by detecting the movement of heat. They detect heat with a pair of pyroelectric elements that turn the incoming heat into a small electrical signal. The pyroelectric elements are wired in the opposite polarity to each other. So the signals normally cancel each other out. But when a heat source moves in front of the sensor, it creates a series of positive and negative pulses that are detected by the microprocessor. The PIR sensor then outputs a HIGH signal to indicate that motion was detected. This signal can then be used to trigger other circuits such as lights, alarms or cameras. 
framorales1924 months ago

Does the sensor receive variable input data. As in different voltage readouts for a heat source as it gets closer and farther away?

No. This type of sensor just outputs a HIGH signal when it detects motion and a LOW signal when it doesn't detect motion.