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[on:]

Hello. I want to design a circuit about dogs and cats by using a motion sensor but I have a problem. In my project; if any person move, motion sensor doesn't work. If dogs or cats move, motion sensor works! Is it possible to do with any sensor? I thought that I could do it maybe using their body temperatures but people's and dogs' (or cats') body temperatures are almost the same. So I have to use another difference to sense the motion. (Is the motion due to the animal?). Do you have any idea about that?

[Reply #1 on:]

Let us know what motion sensor you use.

Is it a PIR motion sensor like the ones that are used in alarm systems ?
That should detect humans and animals, but how good it is depends on the quality.
Some PIR motion sensors can be set to 'high' or 'low' sensitivity. The 'lens' that creates the bundles in front of the PIR sensor has also a large influence on the sensitivity.

A good explanation is here: http://www.ladyada.net/learn/sensors/pir.html

edit: I misunderstood your question. After reading the post by Magician below, I got it. Perhaps you can use a special 'lens' or use tape to select a beam below 1m and another sensor for above 1m.

[Reply #2 on:]

I'd use two PIR sensor, one can "see" movement below 1m, another one >1m. Than 1.0. - animals, 1.1. - human
 It's leave a question how to distinguish child. 

[Reply #3 on:]

Magician ; can you explain your idea detailed? How can I use PIR sensor in way you mentioned? (Where should I put the sensor etc.)

[Reply #4 on:]

O'K, for example you have two PIR,  like this http://www.sparkfun.com/products/8630 . I'd attach one of them to the wall ~1m from the flour,
and second one right above the first. Than piece of cardboard or wood 30 x 30 cm should be inserted in-between to separate vision fields. Other option, use a desk surface, mounting one PIR on the desk and another below or under. The idea, that adult human will always trigger both sensors, though short "waiting" delay could be set in software, to leverage difference in time response.  When 1 PIR trigger, software could wait 1-3 sec if second trigerred as well, before make a decision animal?human.