Reducing the sensitivity of a PIR sensor?

Question

I have several of these PIR sensors.

I am hoping there might be a way to reduce range/sensitivity to a very small field. Currently they are detecting motion about 15-20 feet away.

Does anyone know of a way to reduce the field as low as maybe a 1 foot radius?

I am using them with an Arduino Mega 2560 or an Arduino Uno.

I have tried placing various objects / films in front of the sensor.

Running the sensor through a tube (cardboard or PVC) seems to effectively reduce the sensor to a very narrow beam of detection, however I also need to reduce the overall range, as even with through the tube the sensor fires off at 15-20 feet away. I have tried placing plastic wrap or the reflective static free plastic that electronics are shipped in over the end of the tube, these do not seem to do the trick.

Answer 1

You can attenuate by using thin sheets of polyethylene. Polyethylene is the same material that the PIR lens is made of. It will pass, but attenuate the wavelengths you are interested in. Find something around .015" and begin stacking until you hit your desired range.

Here is a source: http://www.mcmaster.com/#polyethylene-plastic-sheets/=hc4uvj

Answer 2

You can either do this physically using an IR opaque material as Jason suggests, or electronically by modifying the sensor.

Most (all?) of these small PIR detectors seem to be based around a BISS0001 chip. These have two amplifier stages for taking the signal from the PIR FET. If you take a look at the example circuit on page 4, most of the detectors I have seen follow this almost exactly, down to the component labels being the same.

The resistors don't always seem to have the same values on the boards. But by simple observation, you can see that for opamp OP1, it is operating in non-inverting mode. The gain is R7/R8, 2M/47K or approximately 20x.

OP2 is in inverting mode and the gain is R5/R6, 1M/10k or approximately 100x.

I would adjust the values of R7 and R8 to reduce the gain and make the device less sensitive.

Alternatively, you could adjust R1 (connected to the source of the PIR detector) or try reducing Vref (which sets several of the voltage references inside the chip).

All of these require removing and adjusting components though, so maybe the physical way is easier.

Answer 3

black film may be transparent to Infra Red ??

If you can access the load resistor across the PhotoDiode, (PD), then you can change the gain of the receiver. Since light generates current, gain is proportional to R. PD is always reverse biased with R to V+.

Or if using BISS0001 chip reduce 47KΩ in spec sheet. or feedback resistor between pins 16,15. http://www.ladyada.net/media/sensors/BISS0001.pdf

I remember designing a light sequencer in the 70's using a cheap electret mic inside the drummer's kick drum. Needless to say it was too sensitive. So I taped the aperture and the string of spot lights which spelled the band's name sequenced with the beat of the music. It worked well until they changed the sign to 1kW spot lights, and then the triacs burnt out.

Answer 4

I worked around this problem by using a prescription pill bottle and foil tape (the kind used for sealing heating ducts):

1. Cut off the top and bottom of the pill bottle.
2. Wrap the foil tape around the cylinder with a bit hanging off the one end
3. On the end with a little extra foil tape, connect that towards the PIR sensor

In my case the cylinder creates a field of view approx 2 or 3 feet wide and about 12 feet long (maybe less).

--paklids