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Hi , I would like to have assemble a thing that uses this. 
http://www.dfrobot.com/index.php?route=product/product&path=36_58&product_id=119#.UMUgjBfDjZf

but instead of the alarm it is a switch that turns on. 
what are the other things do i need to have it work.
means it activate when it detect a movement.   

the switch is not selected yet,
one option is an electro magnet : 1v, 1 amp, 40m wire, of diameter 0,81mm. 

and idon't know what else is needed to answer this.   

thanks for you time
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You need to provide the sensor with 3 to 5 volts.

The output of the sensor can be used to drive a very small 4V relay or, with a transistor and resistor, drive a 5V relay.

The transistor you need will depend on the current needed by the 5V relay.
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 thanks,

what does very small 4v relay is in comparison to the magnet I described,
0,81wire,  40m 1v 1Amp

is it all, the battery, the IR detector, and the relay, on 4v
or adding a transistor if on 5v.
no controller.




 

 
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Quote
If anything moves after that period, the 'alarm' pin will go low.

What means "anything"? To me, this is a very poor description of what this sensor is
supposed to do. It says infrared and motion sensor, but it looks like a PIR [passive infrared]
sensor, and if it is, then it only responds to "heated" objects moving - like humans and
maybe animals and maybe flames.

For the price, you can buy one and see if responds to "anything" moving, or only to
humans, etc.
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> what does very small 4v relay is

Since the documents only say that a HIGH output is 4V and don't specify a current limit I would look for a relay that will activate on 4V at 20 mA.

> in comparison to the magnet I described, 0,81wire,  40m 1v 1Amp

Look for a relay whose contacts can handle 1A r more at 1V or more.

> is it all, the battery, the IR detector, and the relay, on 4v or adding a transistor if on 5v. no controller.

Correct.  No controller needed if you only want to close a relay contact.  The sensor will run on 5V.  The output of the sensor is enough to activate a transistor.  If you have 5V for the sensor you also have 5V for the relay.  The transistor can be chosen to provide as much current as the relay needs so the relay coil current is not critical.  That will allow you to pick a less expensive relay.




 

 
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John, can you tell if it's PIR from the description?
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John, can you tell if it's PIR from the description?

Appears that way from the picture.
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thanks,

it is for outside use, but inside a box, air circulate, over 32Farenheit or 0celcius.

when outside air is hot, will the IR see changes.

if you have suggestions for a similar product, but very low definition camera.  I may check.
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If it is actually PIR, the way they detect motion is by having 2 sensors and detecting
the difference in readings between the 2, as when someone is moving. I would
assume hot air will be picked up equally by both sensors, and therefore the difference
in readings will be zero, but a moving candle being small should activate it [I think,
but I've never tried a candle].

When you get the sensor, you should do some tests, such as seeing if it will detect
a moving object that is not hot, like a large piece of cardboard waved in front of it,
or whether it only responds to warm body moving.

You might also try to get a datasheet from the vendor.
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I ran across what looks like the identical unit, and this one definitely says PIR,

http://www.makershed.com/product_p/mkpx6.htm
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thanks,

what DC power source could i use
If I want to use th IR with a 0.25 Amps magnet, on 4Volts.

does 2 or 3 AA battery would work.
or other precise type of battery.


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Documentation link on the maker page to Parallax indicates it works at 3.3-5V
and 3 mA.

http://www.parallax.com/Portals/0/Downloads/docs/prod/audiovis/555-28027-PIRsensor-v1.4.pdf
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