IR Sensors

[koossa]

Good day Picers!!

I've got a relatively small amount on knowledge with IR Sensors.
I want to build a motion detector system where I put 2 sensors about 1m appart from each other and connect them to a PIC.
If both of them are triggered, I want to activate an alarm.

Is it better to build my own sensor system using 2 separte sensor components or easier to use 2 fully compiled sensor units for this project?

Thank you
Koossa

[BrianT]

You talk of a "motion sensor". Do you mean a human presence/absence detector or a velocity measurement system.

If you are looking for humans, the easiest is to buy two ready to go PIR (Passive Infra Red) sensors. These are $10 and up and give a saturating transistor as the output. Harder to use, but more versatile, are the $30 thermopiles from companies like Melexis (which I use). Thermopiles can measure temperature remotely while the PIR style just detect a thermal anomaly and turn on the output transistor.
The thermopile approach requires you to build a reasonably sophisticated high impedance, very low leakage op amp circuit.

Tell me more about what you are trying to do and I can explain further.

HTH
Brian

[koossa]

Hi Brian

Thank you very much for your feedback!

Yes, I am talking about human presence/absence detector.
I just need something that will be reliable and it's for outdoor purposes (for security).

Do I need 2 sensors, or will one be reliable enough?

Thx a lot!!
koossa

[grounded]

Koossa I use PIR motion sensor with PIC chip for game cams the PIR I uses is about $10.00 and gives a 5v output I add a 10k pull down resistor that I use to trigger a Interrupt and operates the cam.
I get them from electronics123 I think the item # is cps76 kc7783 PIR detector

here's a link to some of my stuff
http://community.webshots.com/user/richardslaton
If I can help let me know
grounded

[koossa]

Thank you very much Grounded, I will take a look!!

[koossa]

Hi Picers!!

I want to use this motion detector for security purposes (detect human motion)

When putting a fresnal lens over the PIR Motion sensor it increases the detection distance.

Without the lens I will get about 10 feet detection distance and with it about 20 yards.

My question is, will the motion detection be more reliable without the lens if I only need 10 feet detection distance?

Thank you very much!!
Koossa

[grounded]

from my dealings using PIR 's they are very unstable with out the lens
do a search on the web they make a lot of lens wide angel, long range etc.
and diffrent focul lenghts.

[koossa]

Thank you very much Grounded!!

[koossa]

Grounded

According to the electronics123 catalog the "PIR Movement Detector Module" (KC7783) has a fresnel lens already integrated.

Here is a piece of their description:

"A pyroelectric sensor module which is developed for human body detection. A PIR detector with a fresnel lens are mounted on a compact PCB tohether with an analog IC...."

The detection range is 3 meters, do you think this module will be reliable if I connect it to a pic without any additional fresnel lenses?

Thank you koossa

[grounded]

yes it does. what testing I did with the factory lens it work fine but did not have the distance I need the little lens just pops off and I set it up with a new lens and I get 20 yards. I think they are used by a of lot robot builders you mite check some of there forums. the range they use is more like what you need.
if I can help let me know
grounded

[koossa]

Thank you!!

[Jimbo]

If you are planning to use a PIR sensor outdoors, be aware that they tend to
pick up *ANYTHING* moving. I have a neighbor with PIR-activated spotlights
and the things go on every time a field mouse sneezes or a bug flys past and
momentarily blocks some more distant heat source.

PIRs respond to a *change* in temperature, take one of the little plastic lenses,
bend it like in the unit and move past a light source. You'll see that they're
designed to create a parade of little images that slide past the sensor. A moving
object will cause a hot spot to reach the sensor, then there's a null, and then
the next image comes by. The 'sensitivity' setting on some sensors generally
sets how many times the hot spot has to come by in a given time to trigger the
device.

The best way to get around the "Sees everything" problem is to use two or
more sensors set to have somewhat overlapping fields of vision in the zone
you're interested in. Hook the outputs up "AND"-style, so both sensors must
be activated at the same time before you register a positive hit. Likely, a
mouse or whatever will be in view of one sensor but not another. Aiming them
at slightly different heights - say 3 feet and 5 feet - is also useful since all
but midgets will trigger both, but a dog or cat or mouse won't be tall enough
to trigger the 'high' sensor.

An alternative to PIRs or straight thermopiles is to use an IR "distance sensor".
Sharp makes a lot of these, and they're pretty cheap and straightforward. If
you've ever been in a public restroom with the automatic urinals and sinks,
this is what they're using. They work on 'triangulation' - an IR beam goes
straight out and then the reflection hits a photodiode strip behind the receiver
lens. Close objects illuminate just the cells at the edge of the strip wheras a
more distant object is fully "in the picture" and illuminates more. Max range
last time I checked was about four feet - and I've got part of a PBP program
for reading them. In theory an external lens can extend the range somewhat
at the expense of accuracy.

They ARE pretty accurate too, about 1/10th of an inch through most of the
operational range. Won't work if the optics get fogged-up though. Got 'em
from some robot-supply company. Some models supply a 0-3vdc output
you can use with any PIC with an A/D converter. Others source current.
I don't recall if any output a frequency-changing pulse or not.

http://www.mouser.com/search/ProductDetail.aspx?R=GP2Y0A02YK0Fvirtualkey5685000 0virtualkey852-GP2Y0A02YK0F

http://document.sharpsma.com/files/gp2y0a02yk_e.pdf

A related cheap way to sense someones approach is to buy one of those
"ultrasonic rulers" from the hardware store and wire into it in some way.
I've seen some for $19.95 and they sport a range of 12 to as much as
25 feet. HOW to hook 'em up would depend on the exact model and
what kind of info you want from it. They're a fairly narrow beam, so
interference from nature is reduced. Alas, a hard rain might reflect
back enough of the ultrasound beam to create false data. Thermal
sensors aren't so easily fooled by rain.

-Jimbo

[koossa]

Thank you Jimbo!!!!