# PIR sensitivity reduction



## typoagain (Feb 27, 2012)

I have just finished building a couple of 4 channel learning controllers.
I also bought a couple of PIR boards from Radio Shack (surprised that the price was only 20% higher than Mouser. Witt shipping Radio Shack was actually cheaper.)
The PIR sensors have 2 different distance settings; 30' and 15'. What I really want is a narrow field of view and about 5'-6' of distance. I do not want to trigger a startel from 30' away.

I was going to try to mount the sensor in a box looking out a short tube. I figured this would help hide the sensor and narrow it's field of view.

Does anyone know of a way to reduce the distance sensitivity?

Will having the sensor looking through a 1"-2" tube have much effect?

Any suggestions would be appreciated.


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## Otaku (Dec 3, 2004)

I use 1" I.D. plastic tubes, about 4" long, to restrict the field and it works really well. Even at long distances you pretty much have to cross the line in front of the tube to be detected. Distance sensitivity is another problem, even with the tube in place, my PIR's (essentially the same as the RS ones, but without a distance switch) will still detect at ~20 ft. I can't think of any easy way to reduce the detection distance without possibly reducing trigger reliability.
Take a look at the board and see what is going on when you switch to the lower distance setting. Try to see which component(s) are being enabled/disabled when the switch is toggled. If it's a different resistor, for example, that is being switched in to reduce the distance, maybe a higher value one would bring the detection distance down to where you need it.


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## corey872 (Jan 10, 2010)

Good thought from Otaku as usual. A lot of sensitivity issues - either greater or less sensitivity - can also be addressed by aiming the sensor. In this case, is it possible to aim the sensor at the ground or at some 'dead' area about 5-6 feet away? ie - if the sensor is looking across a path, can you aim it at a tree or other object (ie a strategically placed a prop) on the other side to blind it from seeing further?


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## Otaku (Dec 3, 2004)

I use the aiming thing, too. I had a startle prop firing unexpectedly until I realized that people on the sidewalk 30 feet away were triggering it, due to a high angle on the PIR. Relocating and aiming the PIR at the ground fixed that.


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## HomeyDaClown (Oct 3, 2009)

One way I have used is to attach a pvc coupler with a diameter big enough to cover the round lens like Otaku's idea, then I attach it to a stake or pipe about 2 ft. above the grounde and aim it at the ground on the other side of the path. By adjusting the angle you can limit the range of the sensor to just about anything.

Another cheap and dirty way to do this is to just cover most of the lens with electrical tape leaving only a small area (slit) exposed. This combined with angling the sensor to point downward works well.

You could also do the same thing across a corner path.

adafruit.com is seling a PIR module for $10 with adjustable on delay and adjustable sensitivity that may work as well : http://www.adafruit.com/products/189


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## Otaku (Dec 3, 2004)

Homey, that sensor rocks. Thanks for posting this. I have a number of PIR-triggered 2-stage timer boards that run on 12VDC, I could eliminate the 5VC regulator (and associated caps) from the board with this little guy. Sweet!


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## typoagain (Feb 27, 2012)

HomeyDaClown said:


> One way I have used is to attach a pvc coupler with a diameter big enough to cover the round lens like Otaku's idea, then I attach it to a stake or pipe about 2 ft. above the grounde and aim it at the ground on the other side of the path. By adjusting the angle you can limit the range of the sensor to just about anything.
> 
> Another cheap and dirty way to do this is to just cover most of the lens with electrical tape leaving only a small area (slit) exposed. This combined with angling the sensor to point downward works well.
> 
> ...


Wow, that is a very nice sensor for the price.

I was planning on using it next weekend in an open room, specifically a convention hall. I think that aiming it may be the way to go. Only I think I will put it in as box under the edge of the table and aim upward. I am trying to get it where it will fire I you are within 3-4 feet.

What is going on is that I am going to The Academy in Conroe Tx. I wanted to be able to show it to a guy there who has helped me in the past. Anyway I am trying to throw together a quick and dirty demo unit. All it will do is to light up some LEDs.


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## ScaryLane (Jun 3, 2013)

This year, I'm trying out these smaller "Mini-PIR" that are only .5" round and 1" long. Very easy to hind them inside a small prop or other hiding place. Oh the price, they are about $7.00 each with shipping.

So far, they work for me needs in a yard haunt.

Steve


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## typoagain (Feb 27, 2012)

ScaryLane said:


> This year, I'm trying out these smaller "Mini-PIR" that are only .5" round and 1" long. Very easy to hind them inside a small prop or other hiding place. Oh the price, they are about $7.00 each with shipping.
> 
> So far, they work for me needs in a yard haunt.
> 
> Steve


 that is about the size of the one I bought. It was a bare circuit board with the sensor on it. I paid 9.95, but I bought it at Radio Shack. I did not mind the extra cost because I need it right then and I did not have to pay any shipping.


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## ScaryLane (Jun 3, 2013)

I took a look at the radio shack PIR you got (It's a Parallax PIR Sensor) and it's much larger then my mini-PIR. Your PIR is on the left and the Mini-PIR is on the right.








As I said, the Mini-PIR was only $7.00 WITH shipping and there was NO TAX. (Your PIR from Radio Shack was $9.95 plus Tax.)
As you can see, the Mini-PIR is very easy to hide.


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## Otaku (Dec 3, 2004)

Sweet. The small size would sure take care of hiding and aiming issues - you could pinpoint your victims with those sensors. What voltage do they require?


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## typoagain (Feb 27, 2012)

ScaryLane said:


> I took a look at the radio shack PIR you got (It's a Parallax PIR Sensor) and it's much larger then my mini-PIR. Your PIR is on the left and the Mini-PIR is on the right.
> 
> 
> 
> ...


WoW! That is tiny! I gotta get me some!


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## ScaryLane (Jun 3, 2013)

After taking a look at my ebay order for these Mini-PIR and found my pricing was in error, in a good way.

I paid $18 (with shipping) for 5 unit. But I only got 4 of the 5 in the shipment. So, my final price per unit on this order was $4.50

The Mini-PIR has just 3 connections...
VCC - +5 Volts
GND - Ground
OUT - TTl (low power) output line

The unit fires up with the OUT line goes high for about 20 to 30 seconds while it takes a reading of the sensor's field of view. After that the OUT line goes low till triggered.

The OUT line goes HIGH when there is something to sense and remain HIGH till there is no motion for 20 seconds. This works well for a system that just want to know if activity for your show element to trigger or wait for the next group to come by. The unit will stay triggered if you have continuous flow of people, like in a maze. (I find a breaking a IR light beam trigger works better for a maze.)

While I will not buy from the same eBay vender again, I did find another vender (with a better rating) that was selling 5 units at $17.98 (with shipping). That's only $3.60 each. Remember, buyer beware on eBay.

To find these little gems, just search for "5X Mini Infrared Pyroelectric PIR Body Motion Human Sensor Detector Module US". If the search does not work, try the shorter "Mini PIR" search.


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## Otaku (Dec 3, 2004)

Cool, thanks for the info. That 20s high output signal could be a bit of a problem for some applications, but the 2-stage timers I use have an adjustable "off" timer that I usually set for longer than that. That secondary timer locks out the PIR after it's triggered, so it doesn't care about the extended high signal.


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## David_AVD (Nov 9, 2012)

Some more info in this thread.


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