Shielding an IR receiver

[Broz]

Hello, I'm new to this forum. This place is great. Some people seem to be a little grumpy but that's probably due to having to repeat themselves hundreds of times. I've searched the forums for the question I'm about to ask, nothing came up in my search.

Anyways, I've made several projects using 38kHz IR receivers for outdoor purposes. I've made security systems, remote controls, etc. The one problem of course is decreased range and false hits when in bright sunlight. I've ripped that little light filter out from some of my old VCR's I scavange parts off of, but, I'm running out of old VCR's, and I've got more projects to build. I've searched the web and found some suppliers of materials, ordered some samples and none work as well as the VCR material. I've used some homemade materials such as black trash bag material to better effect than the materials that I ordered. However, nothing works as well as a recessed cavity and a filter ripped out of an old VCR.

Where can I find a material as effective as the VCR filter? I'm looking for ordering material, or using household material that is readily available.

BTW, it's a 940nm 38kHZ IR receiver, so any material must be transparent to 940nm radiation.

 

[audioguru]

Vishay make IR receiver ICs in a black case that reduces visible light.
Sunlight has lots of IR so you can't filter it.

 

[Broz]

I've heard that the Vishay's are better than the Panasonics I'm currently using. I'll have to try those sometime. As far as filtering, I have success with the filters ripped out of VCR's and trashbag material that works about half as well. It's just that I ran out of VCR's to scavange those parts from. So, filtering works to some degree. I'm trying to find material that works as well as my scavanged parts.

 

[justDIY]

browsing around the website for the supplier of your ir receiver might yield some app notes for reducing solar interference in outdoor applications.

problem with filtering the Sun is it generates plenty of radiation in wavelengths that will easily pass your filter, flooding the receiver - which is what the 38khz carrier is supposed to combat, since sun is not modulated.

positioning of the sensor so it won't receive direct or strongly reflected sunlight is going to be your only recourse. you can also try using something like PVC pipe to make the sensor more directional, so it's not being blinded by the sun coming in at obscure angles

 

[philba]

I have read that fully exposed photographic film (i.e. black) is actual quite transparent to IR and opaque to the visible spectrum. Easy enough to test - get a digital camera and look at an IR source. Then pass the film in front of the IR source.

There are lots of places that sell filters but they are pretty expensive.

If you find a commercial source please post it back here.

 

[Broz]

Philba, great tip! Thanks. I've tested out the fully exposed, developed negative of a film and it works using the digital camera. Now I have to test it on my various circuits. Only problem is we won't have intense sunlight here for a few days. I'm optimistic however given the tests I've done so far. Thanks again for the tip.