I am trying to construct some small (5 components) IR proximity sensors. They depend on IR light reflected from an object (or lack thereof). I cannot find a suitable material that will block the IR emitter light from directly striking the IR detector and causing a false trigger. In my prototypes, I used several sheets of heavy card stock, but it is not practical to use this in the final circuit. I have also wrapper the emitter in black electrical tape with limited success.
What I am hoping for is a tube that will fit over the IR emitter, and ideally the tube would be some everyday material. I don't (can't) spend a fortune on "IR blocker 3000" or whatever. Thanks for any suggestions
I had the same problem. In the local hardware store, I found some fairly thick flexible (easy to cut) grey tubing in the plumbing section. The tubing fit over the emitters perfectly, and could be cut to a desired length (and, of course, it was IR opaque). Can't remember exactly what the tubing was called, however, but look around the plumbing section and you should find something.
You could also perhaps find some clear vinyl tubing (again in the hw store) that fits the emitter and wrap the tubing in electrical tape. You may also be able to get _opaque_ tubing in the same section -- such tubing is often sold for compressor use. The stuff is cheap enough that you should be able to experiment with it to verify that it is opaque to IR.
Hobby stores sell brass tubing in various sizes - useful for all sorts of things, and in this case you can make directional 'hoods'. Failing that, construct a baffle from aluminium foil. Many plastics will let through some IR, metal is much more effective - also gives you a little shielding if required.
If you look over the webpages of various commercial IRPD's, you'll see most of them use black heat-shrink tubing. 1 layer seems to work well. You need to cover up all but the very end of the Led.
You might be getting emissions [and therefore reflected signal pickup] out the bottom end of the Led. That IR bounces all over the place. You can get great reflections off a scope probe connected to the ckt, interface wires connected to the pcb, etc.
Some other things I've found, on playing around with IRPD's, are:
- if your Led currents are high [some people use 20 mA or more], then you'll get a lot of extraneous reflection. Use only as much Led current as you need.
- the exact angle between the IR Led and detector module is a factor - you can possibly eliminate direct pickup by slightly changing the angle of the Led. In my IRPD's, I've found I need to adjust the angle slightly during calibration.
- I have a 2-chan IRPD I've been playing with, and if the angle between the detectors is low enuf, and a target is close in on one of them, you can get reflections and pickup on the 2nd channel. I used a piece of black conductive foam between the 2 detectors to block this.
Note that flat black surfaces [like conductive foam] seem to reflect the least amount of IR light. If you tune your system to detect a white card at say 12", then a "shiny" black surface will not be detected until maybe 8" or so, and "flat" black surface at 2-4" or even less distance - varies with exact reflective characteriestics of the targets.
*Thank you* for mentioning this! I was going to before I read your post. The nice thing about the metal tubing (also in aluminum, which I think is easier to cut and a bit lighter) is that you can make long barrels that can effectively limit the beam and/or cone of acceptance to just a couple of degrees. It never sags or is deformed, the way plastic or electrical tape can.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.