Infrared alarm

I would like a little tutorial on infrared alarm ( the simplest possible type)... I know you guys would advice me to google INFRARED ALARM, but trust me I have done that, but there is something about this forum that makes me understand any other thing I read, maybe it is because I know I would always get live help and well 'customized help' when I call, please please I really need this, am still working on my project "population counter", and I think an infrared alarm circuit might give me some hint on what i want to do.. thanks for all contributions..

Well, I can offer this:

There are three types of infrared "alarm" devices (that I can think of):
1. Passive or PIR sensor. A thermal pile coupled with a special multi-faceted infrared lens that detects changes in the ambient thermal background (i.e. it watches an area and if anything changes the thermal pattern, such as someone walking through that area, it toggles a voltage on it's output.) There are varying fields of view and these devices are VERY sensitive. I worked for a guy, back in the mid 70's, that owned a security firm that used these outdoors. I was sent to troubleshoot one installation that kept going off 24/7. When one of these devices would detect something, a very loud relay would click. This allowed me to sit under the thing and watch for what was setting it off. About a mile away there was a freeway that it was pointing at. I noticed that every time a large truck went by it would trip. It was _that_ sensitive! In another case, there was one pointing at a wall that got sun part of the day. During that time, whenever the wind would blow and cool the wall down, the thing would go off!
2. Infrared beam with sender and receiver. When someone walks through the beam the receiver toggles a voltage or a set of contacts (such as on a relay).
3. Infrared laser with reflector. In this case there are, typically, twin beams -- one going to the reflector, and one returning -- interrupt either beam and, again, a voltage toggles or a set of contacts change. The advantage of this over #2 is there is only one active unit, and thus power doesn't need to be run to two places.

Try Googling PIR.

Okay thanks, I really think that PIR would do just fine, but getting this stuff where i am currently might be a little difficult, anyway thanks, I would read it on google and come in for questions if there is need to thanks

sorry the infrared laser seems more interesting, i think i would work with that now thanks

Dont forget to modulate the beam then and check code within the beam every so many cycles Other wise way round this one is simply place another beam in front of the sensor and your alarm system doesent work or fails

Then consider using a retroreflector (sometimes called a retroflector or cataphote). It's a reflector designed to reflect light (i.e. infrared) back to the source -- in other words it puts a 180 spin on the angle of incidence. These reflectors are commonly used on the back of bicycles (and on the moon .

Using this kind of reflector eliminates the headache of alignment. All you have to do is hit the reflector with the laser beam and it bounces back!

Also, because this is such a short range (IR lasers are typically used to cover hundreds of feet), you might get away with an IR LED with a narrow viewing angle (i.e. a highly directed beam). They are available with viewing angle (2Φ0.5) as small as 4°. Such as:

* Digi-key p/n 1125-1035-ND 4° ~$10
* Digi-key p/n 1125-1046-ND 5° ~$11
* Digi-key p/n 475-1200-ND 6° ~$0.50
* Digi-key p/n VSLY5850-ND 6° ~$1.30

Try this
http://www.electronicsforu.com/efylinux/circuit/feb2003/mar02_ir.pdf
It may give you an idea.
It also has a wide range

Hi steve just read your comments re infra red good idea by the way but would still suggest in the case of infra red leds for example, come to that infra red lazors that the gentleman concerened uses a protocol along side this example as seen in the phillips RC5 protocol which utilizes manchester encoding

Possibly including bit flip on bit 3, which in the case of remote controls indicates the depression of another button

In this case for example could be utilised for event detection that is a separate intrusion and subsequently log time of event by writing this event or event log if you like to a memory chip using I2C protocol

He could expand on this further to include serial comms port via ethernet or Serial modem to visual interface via wifi or RF subsequently paging a list of trusties via mobile sms or socket monitered client server software

This would really make a very interesting project not just about infra red alarms but also would encourage interfacing with the outside world on a far broader scale whilst introducing web technologies at the same time

What do you think about this for an idea

Mark Harrington

But, remember, his application is not security but counting people. But, still, some encoding would be a good precaution .. never know when some sort of spurious IR will get into the system.

Hi steve

Thankyou for your input If hes counting persons he needs to construct his mechanism in such a way that he detects forward movement within a sliding window and reverse mechanism for outward bound traffic also within a sliding window Time slot in other words on some type of mechanical one way latched context. Example a locking barrier

The reason why I mentioned encoded is that I was inspecting for interest a set of barriers the other night I happened to notice that if blocked the beam after a vehicle had just passed through I could keep the gate open indefinately

Of course the question arises well what do you do about this, so i came up with the theory of encode the lazor and secondly include a second set of detectors placed at distance equal to maximum permissable length of vehicle to pass though

Also within this where are the pressure sensors built into the road Answer none again even on the barrior crossing there are no pressure sensors or vehicle counters deployed

Reasons being In a high security area if anyone wanted to confuse the system all they would have to do is to cause disruption is place an emitter permanent beam infront of sensor This would prevent barrier opening hence no emergency vehicles could get in under certain circumstances

Keep the gate open for onslaught by blocking the detector and so prevent gate from closing hence encode light path



The other point that crossed my mind was that in any of these events Theres no alarm, in other words no one knows that intrusion has been made so where is the connection to the real world or if you like advisory signal telling operators that a high security zone has been breached, answer there is none

Taking this i to account where is the keypad for entry level answer none again

When i thought further I also noticed how do you log vehicle registrations entering and leaving zone One answer might be barcode but sensibly speaking a scratch or dent would render this inoperative so next answer to this might be Rf id good idea but you would have to pre arrange this so only one alternative use the system meaning of course automatically build rf identity into vehicles so that as and when vehicle passes barrier an immiediate request is made to the vehicle which automatically transponds its registration and vehicle particulars to a mainframe similarly you might even go as far as sending a page request to mobile phones or radio transmitters inside the vehicle passengers or otherwise to forward esns mobile phone numbers of all occupants at the same time or arrange rf tagging in the form of a pendant to do likewise

Just ideas at the moment suggestions if you like t

At what stage do you switch on height sensors to feedback that is there even a vehicle there Answer again none

The afore mentioned point would also cover pressure or weight sensors

Also I noticed where is the floodlight automatically switched on when barrier lifts Answer no floodlight

Where are the cameras pointing to the barrier recording entrance of vehicles Answer none again

This by the way is the level of security provided to armed forces personell residing in woolwhich in quite a well to do area typically what they define as the docklands very up market accomodation

Now if i can see this

Question why havent the people who marketed this in the first place

Come to think of it whats the point in having barriers at all if this is the extent of the security provided

A subject to think on if you are really dead keen on producing a security, counter aware system why are they not looking at every possible event and combining this with modern day technology surely if you are going to design such a system dont you consider this in your final design Isnt this what people are paying for?

Leave this open to discussion I hope you find my comments stimulating and provoking thought awareness

These are purely my own observations and ideas but I trust engineers etc will take this into consideration with a view to approaching a design of such a system in the future or re designing, modifying existing security, counter or both applications

MD Harrington

Dear Steve
More information about PIR Sensor ,Pyroelectricity etc Thermal Imaging in these links

http://dmohankumar.wordpress.com/2011/08/29/pir-sensor/#more-4905

http://dmohankumar.wordpress.com/2012/05/03/f...components-part-xvii-motion-sensor/#more-7475

http://dmohankumar.wordpress.com/2011/05/10/thermal-imaging/#more-3870

http://dmohankumar.wordpress.com/2011/02/19/pyroelectricity/#more-2864

Don't tell me ... George is the one with the question

OK Thanks

Dear George
If you want more information about Infrared and PIR, just see

http://dmohankumar.wordpress.com/2011/08/29/pir-sensor/#more-4905

http://dmohankumar.wordpress.com/2012/05/03/f...components-part-xvii-motion-sensor/#more-7475

http://dmohankumar.wordpress.com/2011/05/10/thermal-imaging/#more-3870

http://dmohankumar.wordpress.com/2011/02/19/pyroelectricity/#more-2864

I was kidding!

Hi

I see the information re pir detectors Id like to mention for future design that you now seriously consider using camera ip related or usb cameras in conjunction with software applications where pir, although still used, is now being replaced with image movement detectors using langauges such as C sharp and other langauges. in conjunction with camera technology as opposed to Pir

Some very good articles on the net re this which I stongly recommend that anyone whishing to enter this field read

See below for another interesting link and attached

http://ashishrd.blogspot.co.uk/2006/11/obstacle-detector-using-webcam-and.html?m=1

Mark Harrington

Whoops forgot to attach see below

We have such solution for you:


SensMax is a manufacturer of people counting solutions that provides automatic people counting using
wireless people counters

I visited your site, but I don't see any information about what the technology is. How can I be sure your people counting technique isn't harmful? I mean, I could make a people counter that uses x-rays to feed bone structure images to pattern recognition software that counts human skeletons -- but I would never deploy such a device -- I'm kind of humanitarian that way.