EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Simon on October 10, 2013, 07:06:57 am
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As some will recall I had a topic going on infrared proximity sensors. Well we mostly cracked it and have completed the project but now I'm being asked for so much more range that I run the risk of the sensor picking up permanent fixtures. So I'm thinking along the lines of a PIR sensor now, but i need a fairly narrow "beam" so that again oeripherial movement is not picked up. Can this be achived with a PIR sensor ? Say by putting a tube over it ?
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Tin foil with a slit will narrow the field of view that a PIR for an alarm system or outside light has.
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So your saying pin hole camera lens style ? in our case that would be a suitable length tube with small hole in the end, the L/D ratio being the focussing factor
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what about materials that the IR can go through. I think we would still need to put the sensors behind glass or plexiglass, will they still pickup behind such a barrier ?
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As some will recall I had a topic going on infrared proximity sensors. Well we mostly cracked it and have completed the project but now I'm being asked for so much more range that I run the risk of the sensor picking up permanent fixtures. So I'm thinking along the lines of a PIR sensor now, but i need a fairly narrow "beam" so that again oeripherial movement is not picked up. Can this be achived with a PIR sensor ? Say by putting a tube over it ?
Any PIR sensor amplifier is normally AC-coupled to remove permanent fixtures. This works very well as long as you do not drive the sensor into the corner.
The distance range of PIR sensors is primarily determined by the lens you use. The secondary factor is the amplifier. You can buy wide-angle and narrow-angle lenses. You can block some part of the angle if you use an enclosure that limits the field of view.
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Well we are not looking to have a wide angle which I guess reduces the sensitivity and as most sensors seem to work from 3+m we won't have a problem with 200mm.
Do we need a lens or is using a tube possibly with a cover and hole in it on one end enough to have a basic angle of view determined. These are only for proximity sensing so no zones act required.
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I tried out the cheapo PIR module I got off ebay with a tube over it and taped a piece of cardboard with a pin hole in it. It works quite well. Boss is not too happy on the el-cheapo modules, can anyone recommend any decent ones ? I found that glass is impenetrable and perspex is no good with the tiny hole, what is the material usually used for the lenses ? maybe we can get some narrow beam sensors as opposed to the usual lenses that aim to increase the angle.
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All the PIR's that I have seen all have some type of white plastic over them, most likely polystyrene or polycarbonate. As for sourcing RS have quite a few ranging from £1-25 for just the Diode or whatever it is to £215 for a unit with wireless built in.
http://uk.rs-online.com/web/c/?searchTerm=pir+sensors+uk&cm_mmc=UK-PPC-0212-_-01_HVAC_and_Thermal_Management-_-pir_sensors_Exact-_-pir_sensors_uk&gclid=CJ6Cr8S_jLoCFUXKtAodmjsA6Q (http://uk.rs-online.com/web/c/?searchTerm=pir+sensors+uk&cm_mmc=UK-PPC-0212-_-01_HVAC_and_Thermal_Management-_-pir_sensors_Exact-_-pir_sensors_uk&gclid=CJ6Cr8S_jLoCFUXKtAodmjsA6Q)
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what about materials that the IR can go through. I think we would still need to put the sensors behind glass or plexiglass, will they still pickup behind such a barrier ?
No, Same as for thermal imagers - polythene is the only thing you may be able to get away with, with reduced sensitivity otherwise it's Zinc Selenide, germanium or Gallium Arsenide.
I like these PIRs from Panasonic - small, and internal processing circuitry.
http://www.farnell.com/datasheets/73642.pdf (http://www.farnell.com/datasheets/73642.pdf)
Farnell stock most of the range - price is somewhat variable between models and stockists so worth shopping around
bear in mind PIRs are mostly sensitive to movement across the field of view, and relatively insensitive to motion directly towards/away
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Well we only require a 0-200mm range and the sensors go up to 9m so hopefully plenty of sensitivity. A 25mm tube over the sensor with a 3mm hole in it get a come of view with a base diameter of 50mm at 200mm from the tube end.
The motion will be at 90 degrees to the direction of sight so will create the most "motion".
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..polythene is the only thing you may be able to get away with, with reduced sensitivity otherwise it's Zinc Selenide, germanium or Gallium Arsenide.
I saw a site where you could get colored material for use in fabricating lenses for PIR use. Yes, the poly kind. I imagine you would be able to mold/color it into the look of your liking (say a rock, stump or wall-trim). I know nothing of its effect of the sensitivity of the PIR component (like the NaPion).
I like these PIRs from Panasonic - small, and internal processing circuitry.
http://www.farnell.com/datasheets/73642.pdf (http://www.farnell.com/datasheets/73642.pdf)
That's what I went with. Low power (uA), everything built in, and especially its small size and darker color. Good for security use.. most PIR sensors look like a halved golf-ball, try hiding that. lol. Tested mine with a transistor, resistor and an LED and if I so much as breathed it would give me a light blink. It was at very close range though.. I haven't played with it more yet.
My aim is for creating a device for field surveillance with the qualities of a Trail/Game-Camera (Fast "trigger time" and long battery-life (up to a year)) but using separated components (think CCTV cams).
Can't find any low-power DVR circuitry or schematics though.
Sincerely,
IM