PIR Motion Sensor

Posted on Feb 5, 2014

The objective of this project is to use inexpensive PIR sensor to detect if a human has moved. To build this project I use a PIC18F25K20 microcontroller to detect if the sensor had change state and it will emit a sound from the speaker or piezo, the MCU also detect the voltage of the battery in the startup, the algorithm it s very simple it use a

PIR Motion Sensor
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n interrupt on change to detect the change on the PIR sensor. PIR sensors allows you to sense motion, almost always used to detect whether a human has moved in or out of the sensors range. They are small, inexpensive, low-power, easy to use and don`t wear out. For that reason they are commonly found in appliances and gadgets used in homes or businesses. PIRs are basically made of a pyroelectric sensor, which can detect levels of infrared radiation. Everything emits some low level radiation, and the hotter something is, the more radiation is emitted. The sensor in a motion detector is actually split in two halves. The reason for that is that we are looking to detect motion (change) not average IR levels. The two halves are wired up so that they cancel each other out. If one half sees more or less IR radiation than the other, the output will swing high or low. I use a 9V battery and it s connect to a switch and as a voltage regulator I use an L317T and it will have an output of 3, 3V to make that possible I use two resistors R1 and R2 to set the output, i use this equations to calculate R1 and I set R2 to 240 ohms: I had to add a RC delay on VPP pin because when I switch on/off the circuit there was a voltage drop because the PIR Sensor and that would generate an unknown state when the MCU was restarted to solve that I add a RC delay, you can use this equations to calculate the delay I use an 8 ohm speaker but you can use a...

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