I'm modifying the sensor below to limit it's detection area.
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I have put it in another housing and it is looking through a 1/2" hole. Now to protect it from the weather, I want to cover the hole.
Well... I have found most common household items are opaque to infrared.
Thinking plastic here.
Any idea what the common wavelength of these IR motion sensors is?
Any thought about a common item I might have or can get tomorrow that will be clear to IR? (and hold up to weather)
I did find one* plastic lid to one of the wife's bowls that does a pretty good job. It is not labeled with an identifier, so now I'm very curious what it is. I will work with it tomorrow and see if I have the range I need. Mikek
she's got a cupboard full of many types of lids only one passed my test. PS. What is LLDPE? Low Low?
I set up mine again. Seems most sensitive dead on. I had to cut down on thevolume after trying duct tape, which does not work very well. Used something like 25k in series with speaker. I'd like another if I could get same channel.
The last couple of days with high winds cause cause my unit to trip. First problem, sensor was not mounted tight. It will still trip occasionally. First time I have really played with the thing after owning it for several years.
Yes, they are very loud and tape does not work to cut the volume, btdt. I'm using the receiver to trigger a call switch on a walkie talkie. This is so I can be 300 feet away and get an alert. What channel do you have? Mikek
Try a cheap IR thermometer gun and an incandescent light source (mostly heat) to test if it will pass long wave IR.
If you modified the PIR receiver (that's the one with the translucent Fresnel lens) it's likely that your sensor won't work well. The device relies on the Fresnel lens to produce dramatic changes in IR level to the detector as the object passes by. See link below with explanation of how it works. Maybe a different style Fresnel lens?
7 - 14 um wavelength. The PIR sensor already has a silicon IR filter window. The transmission characteristics of the plastic lens is less than that, so it's the lens that determines the usable wavelengths. Note that they suggest using an unprocessed silicon wafer as a window. You'll do better with a germanium window as found on eBay. $20.50
If you want something that will pass IR and block visible light, it will need to be a germanium or silicon lens. Otherwise, HDPE (high density polyethylene).
Polystyrene will pass the entire IR band. The problem is that it will pass the entire IR band and not just far IR. If you just want a protector, and don't care about passing visible light, try the clear window on a mailing envelope.
The Fresnel lens on your driveway sensor is HDPE. See the list of applications below. Look for something that's sorta translucent and made from a hard plastic. Hard and clear plastic bottle caps for glass bottles would be a good start.
Linear Low Density Polyethylene. If the lids are soft plastic, it probably won't work. I just tried a HDPE cutting board. It passed some IR, but because it was so thick, it was lossy. Look for something made from a similar material.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
I have kept the original Fresnel lens in place, but only because earlier testing showed me I had to! I then found out why.
Maybe the plastic lid I have is HDPE.
I could not make it work with polystyrene, I tried several PS objects and none worked. I was ready to use a CD case.
If the lid I have doesn't pass tomorrow's testing, I'll be searching for HDPE to test. The black bag won't last long outdoors, but as a last resort, it would be easy to replace and stretch a couple rubber bands around every three months. Thanks, Mikek
They'll break down eventually in sunlight. See video at: starting at 2:45. Far IR goes through two layers of black polyetheylene trash bag on a thermal imaging camera.
The rather thin trash bag works well. However, when I tried 4 mil and
6 mil black plastic sheeting (used in construction), it was effectively opaque to far IR.
I also tried the trash bag directly off the roll, which worked out to
8 layers. Nothing went through.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
On motion sensor prototypes at work a layer of 2" wide, inexpensive, thin, clear plastic packing tape was used. . This was to cover a one inch hole on a metal project box. The stuff that is 1.50 a roll at Walmart works fine. They did not even bother to remove the adhesive. Works well on sensing people. The battery powered sensors have been outside for four months now, in a Ohio winter, with no failures.
A overhead transparency of the non inkjet kind would be fine as well. They are a little thick, so you may see some attenuation.
The Roscoe filters are usually gelatin based on a clear substrate. . The water in the gelatin would adsorb at 10 microns, blocking the signal.
You don't need a far IR bandpass filter. There's already a far IR silicon bandpass filter window on the PIR sensor. No need for a silicon, germanium, or garbage bag filter. Anything that will pass IR, including clear uncoated glass, polystyrene, HDPE, etc should work.
Assumption, the mother of all screwsup.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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