Let's Make Robots!

Plastic thats invisible to IR light?

There are lots of great and interesting little robots on this site and on the web, but so many of them use the sharp IR detectors that they all start to look the same. I wanted to do something different and a bit more aesthetically nice, so I thought what if I could get some plastic thats transparent to IR. Then I could hide the IR sensors behind them and completely change the look.

The dome lenses on cheap PIR detectors are clear to IR but they aren`t big enough for what I want. Does anyone know where I can get this stuff, or even what the technical name for the plastic is? Maybe there are some plastic things around the house that could be used. Or some paint that passes IR but not visible?

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I've found a shop on the internet that sell sheets of IR filters, havent tried them though.

http://www.alanaecology.com/acatalog/Infrared_Filter_Sheets.html

/Thomas

I have stackable plastic bins that I use to keep toys, and i've noticed IR goes right through it. I got them at a big box office retailer like Target or Office Max.

You might be able to find the opaque sheets used as filters for 35mm or larger format cameras at online camera shops.

Back in the day I used this stuff when attempting my hand at ir 35mm film. It was a square dropin filter that would go into a holder mounted on the front of the lens. visible light was completely removed....You'd get some amazing photo's....too bad it was expensive to develop....

Not sure how special the filter was but it claimed to only allow ir light through.

Do you remember how much the filter cost?

This website I found has some good information on reflecting transmitting or absorbing visible and IR light. They suggest using developed but unexposed film, or layering red/green/blue plastic sheets together. I`m going to stop in at the dollar store today to check their coloured plastic.

Anyone have any insight into how film developing at the shops work? I mean if they end up with much scrap film like when people develop a roll thats not finished.  I don`t want to have to buy some film then get it developed just to see if it works.

 As a follow up in case anyone else is interested, I did some preliminary tests with a remote control and the camera on my phone on some clear red and green plastic at a stationary shop. The results were promising so I bought them.

You can see below the normal output of a sharp IR and then with both red and green sheets flat against the sensor. The loss of brightness was ever so small, less than my picture shows. I think I just messed up the camera angle in the 2nd shot because I was trying to hold 10 different things at once.

Using the arduino and both sheets the maximum detection range is down to about 50 cm and the time it takes for the readings to stabilize after something is detected jumped about 5 secs. Pretty unacceptable sadly. But with only 1 sheet the max range returns to 80cm and the wait time is under a second.

I had hoped that because the sheets are within the minimum detection range it wouldn`t be affected this much. The sheets are 0.5mm each so 1mm stacked. I think the beams moving when they enter and exit the plastic, or partial refraction inside the plastic is messing it up. I might try 1 sheet of much thinner stuff like black cellophane if I can find it.

P1000788-500.jpg

P1000789-500.jpg

Since most sensors also respond to visible light as well as IR, the "dark" plastic filters out the visible light waves. this gives better results for IR only.

Expsoed 35 mm color film was also used as an IR filter in the past.

I would assume any clear plastic would work. IR light is well... light. Anythign that lets visible light pass through should let IR through.
I guess he means that blackish plastic that only lets IR through. You can find it on some remotes but it's quite small.
You would have to experiment. Find some dark purple or dark blue plastic and see how it affects the range the IR can be detected. Now that I think of it the IR sensors I got from tech-supplies have a dark plastic over the sensor.
He`s right, I want to hide the sensor behind some opaque plastic without affecting the IR light. Sorry I should have been more specific.