Wednesday, April 15, 2009

PIR Infrared motion detector Circuit

Infrared motion detector Circuit
The pyroelectric sensor is made of a crystalline material that
generates a surface electric charge when exposed to heat in the
form of infrared radiation. When the amount of radiation striking
the crystal changes, the amount of charge also changes and
can then be measured with a sensitive FET device built into the
sensor. The sensor elements are sensitive to radiation over a wide
range so a filter window is added to the TO5 package to limit
detectable radiation to the 8 to 14mm range which is most sensitive
to human body radiation.
Typically, the FET source terminal pin 2 connects through a
pulldown resistor of about 100 K to ground and feeds into a two
stage amplifier having signal conditioning circuits. The amplifier
is typically bandwidth limited to below 10Hz to reject high
frequency noise and is followed by a window comparator that
responds to both the positive and negative transitions of the
sensor output signal. A well filtered power source of from 3 to
15 volts should be connected to the FET drain terminal pin 1




Application Schematic of Pyroelectric Infrared Motion
Sensors Circuit
Note: For best results the power supply should be very stable
at a constant +5V DC +/- .2V.This Schematic is offered for reference only without warranty
of any kind. Microsystem Technologies does not support user
designs or implementations that use this circuit


Automatic security lights Circuit
Combination PIR sensor and floodlight units are cheap but
rather inflexible if you want to locate the sensor and light in
different places. In my case, I wanted to detect movement
on the driveway and switch on the lights in the carport around
the corner. Yet another job for the ubiquitous PICAXE-08

A standard PIR sensor is used as the movement detector.
The sensor interfaces to the PICAXE (IC1) on input 2 (pin 5).
This pin is pulled low via isolation diode D3 and the normally
open (NO) output of the sensor whenever movement is
detected. It can also be pulled low by transistor Q1, which acts
as a simple inverter for sensors with normally closed (NC) outputs.

Passive Infrared Motion Detector Circuit

This circuit was originally reverse -engineered from a motion
detecting yard light that I ripped apart. That's still probably the
best way to get the parts at a reasonable price, especially the
pyroelectric sensor and the absolutely necessary Fresnel lens.
The signal at pin 7 of the 324 is very interesting and fooling with
the filtering around the first amplification stage can make it even
more so. The LM324 is a wonderful little bug, and you will find
many uses for the window comparator if you look at it the same
way you would learn a new really useful knot. It all works on a
single 5 volt supply. The sensor is only sensitive to changes
across its surface, so don't expect a signal from a static object
even if it is hot. Yard lights are turning up at flea markets and yard
sales as people find themselves heads up every time the cat walks
past. This circuit is in a machine that sees people moving 40 feet

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