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Motion-detector-sensor-circuit

audioguru

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It detects IR light or heat. It might not detect a person who is fully dressed.
 

Nigel Goodwin

Super Moderator
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It detects IR light or heat. It might not detect a person who is fully dressed.
It's just a standard PIR, as used in security lights and burglar alarms, of course it detects people that are fully dressed :banghead:

fixit7 - it's only 'simple' because all the clever electronics is in the PIR module.
 

AnalogKid

Well-Known Member
Most Helpful Member
A close-up view of the *inside* of the dome would help. Usually, the sensor is surrounded by something that looks like a picket fence or lattice. As a heat source moves by, the webs of the lattice create moving shadows on the face of the sensor, so a moving source appears as a squarewave. This AC signal is what is detected as "motion".

ak
 

Mickster

Well-Known Member
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If you click the link, the image just about shows a honeycomb pattern on the inside.
 

fixit7

Member
It detects IR light or heat. It might not detect a person who is fully dressed.
PIR sensors can detect small amount of variation in infrared. Whenever an object passes through the sensor range, it produces infrared because of the friction between air and object, and get caught by PIR.
 

AnalogKid

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Most Helpful Member
PIR sensors can detect small amount of variation in infrared. Whenever an object passes through the sensor range, it produces infrared because of the friction between air and object, and get caught by PIR.
No.

That is not how infrared sensors operate. Air friction does not contribute in any way. A human body surface temperature is around 80-90 F, while the ambient air around it is 70 F or whatever. That difference is what the detector "sees". Friction adds less than 0.01 degrees, and is not detectable without highly specialized equipment.

ak
 

fixit7

Member
I do not know what to believe. ?

Wiki says this

Operation
A PIR sensor can detect changes in the amount of infrared radiation impinging upon it, which varies depending on the temperature and surface characteristics of the objects in front of the sensor.[2] When an object, such as a person, passes in front of the background, such as a wall, the temperature at that point in the sensor's field of view will rise from room temperature to body temperature, and then back again. The sensor converts the resulting change in the incoming infrared radiation into a change in the output voltage, and this triggers the detection. Objects of similar temperature but different surface characteristics may also have a different infrared emission pattern, and thus moving them with respect to the background may trigger the detector as well.[3]
 

audioguru

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Most Helpful Member
My eyes are a PIR sensor when a pretty young lady walks past wearing not much revealing clothing. My eyes are blind to an ugly lady completely covered up, just like I think is the same as the sensitivity of a PIR sensor, it detects uncovered flesh, not clothing.
I think a person walking in front of a PIR blocks background IR radiation which also causes the PIR to detect the mottion.
 

SPDCHK

Member
I love using the RCWL-0516 Microwave Radar Sensor
If you want something that can detect movement behind glass or dry walls try it.
It detects the movement of moisture. Very sensitive. It will detect a pigeon walking past it. Unfortunately in extreme foggy conditions or heavy rain falls, it also detects that and can then give false alarms
 

GromTag

Active Member
(restate) PIR sensors trigger when ambient temperature is shifted enough from stationary or humidity changes in erratic behavior. Humidity can throw temperature as well.

Some types of clothing are invisible to PIR, Rayon, and some Nylon blends leaving only small exposed areas to be potential detection for the PIR, mostly the face, wrist, ankle areas, unless wearing a certain material cover over those exposed areas.... The temperature difference is there trough the material yet not likely to be an adequate enough to result a detection with some PIR sensors. Or adjustments made to reduce false positives.

Many other sensors can false trigger as well. (Options) Multiplexing is costly yet can reduce false triggers. Strain gauge + detection + audible, make for a decent assurance against false spikes as no weight on the strain gauge or plate would cancel a false from the others and so on. Yet having multiple sensors can result in more that can go wrong with the sensors themselves. It's never easy to build any foolproof system.


The RCWL 0516 does show to work based on the method of the transistor oscillator, Colpitts based design. (have used a few)

The module functions like an X band module that has been folded with the output on one side and the receive on the other.

However

The RCWL is an inductive based environment reflection concept.

Inductive objects entering the range alter the return signals causing the oscillating transistors base to fluctuate as the pcb trace is the inductor that completes the oscillators function to operate. It's metaphorically a " pull " generator. The transmit (non component) side transmits each pulse at frequency pulling a small value from the transistor side setting a level, the rest goes beyond sample converse.

As is to why the sensor can perceive inductive objects from the sides at considerable range.

Rain droplets can cause enough reflection value to result in a false output when "close enough" to the RCWL. Have not had an issue with rain yet, no sensors are mounted close to any exterior for possible faults caused by rain or equivalent.

Just note if used that the transmit side is the non component side and the receive is the component side. with a bit of signal tunneling through the pcb. Tho the signal can sometimes transmit through what is behind the board (RCWL logo side) if placed against a wall as an example.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Jesus! - there's a lot of discussion here about nothing :D

They are PIR modules, just the same as used in millions of commercial applications - I've used these exact modules, and they work perfectly, just as all the other PIR's do.

Their mode of operation relies entirely on the fresnal lens in front of the sensor, and they work great.

There was mention of microwave detectors above - these are also used in burglar alarms (more expensive and professional ones), BUT they are usually as part of a dual PIR/Microwave sensor, which require BOTH units to be triggered to avoid false alarms.

The alarm I installed at work (which was cheap) came with PIR sensors, as expected - but there were already remnants of a previous professional alarm in the building, and I added the existing PIR/Microwave sensors as well :D
 

audioguru

Well-Known Member
Most Helpful Member
I have used only one PIR alarm. It was used to sense a person entering an open loading dock. It was sensitive enough to sense a person who was fairly close to it but not too sensitive to give false alarms. It did not detect a dog. I did not notice if winter clothing affected its heat sensing.
 

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