Hi, I am in my final year of elecrtonics at college and I need help on my project for this year. My project, as you can see in the subject box, is a motion sensor alarm.
I need some basic information on the sensors I can use. I think there are two types of sensors I can use, which are PIR (pyroelectric infrared sensor) and Passive-Optical Person sensor. Can you please give me links or basic knowledge on how these devices work. I would be very much appreciated. ...

Hi Deepan,

Motion sensor.

If your electronics examiner would be happy for you to purchase
the chips and solder together the support circuitry, then a
passive infra red unit would be very easy to make.

However on the other hand if your electronics examiner actually
expects you to design and build a motion detector using general
type chips, and/or regular components, then i would suggest that
a 'sonic echo' type might be easier to construct.

In case you don't know the principle, it relies on doppler shift.
A note is produced and sent out into the air with a small speaker
or tiny transducer.

All the returning sound within about ten percent of the original
frequency is amplified with the original frequency removed.

Any movement makes echoes which are only slightly different in
frequency to the original, and its these which cause a response
from the unit.

These units used to be fairly common, but you don't see them much
now. The construction is basic, and fairly easy to understand.

The electronics involved in a passive infra red sensor is a higher
level of complexity.

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After looking around a bit, i found this:
http://www.ee.washington.edu/consele...l/proposal.htm
Which describes a project very similar to the one you outlined.

It gives an excellent explanation of the 'Ultrasonic movement
detector'

I was very struck by the simplicity of construction of their
proposed infra red motion detector, until i read through it again.
Then i realised its only a beam.
Their sensor responds to the interruption of a beam.
I don't think that is quite what you have in mind.

A PIR motion detector seems to be quite an involved electronic
system,
http://www.holtek.com.tw/pdf/consumer/761x.PDF
even putting together the support components looks quite difficult.

************

Best of luck with it,
John

Thanx for the help john. :lol: