Infrared LED filter

Thread Starter

Tejasvi471

Joined Jun 9, 2020
14
Hello community,

I am thinking to purchase IR led and detector (attached datasheet).
Is there any way to filter out all frequencies but one coming out IR LED,
I know it is impossible to achieve single digit frequency, it will be more of band of frequencies.
This IR LED peaks at 940 nm, its Spectral bandwidth (Δλ) is 30 nm.

I want 2 output bandwidth

1) Δλ -10 nm peaking at 920 nm and
2) Δλ -10 nm peaking at 940 nm

My second question is for PT333-3C photo transistor which will serve as detector.
Its detection spectral Bandwidth is 400 nm to 1100 nm peaking at 940 nm
as far as i can see it will detect both bandwidth easily.
 

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Externet

Joined Nov 29, 2005
1,493
Televisions and their remote controls have infrared-pass plastic windows in front of their sensors, sometimes in front of the emitters too. Canibalize them from defunct units and check if they work for you.
 

Audioguru again

Joined Oct 21, 2019
1,488
The 940nm or 920nm have no tolerance. If the 940nm is +/- 10% then it could be from 846nm to 1034nm.
Of course the phototransistor will pickup both of them.
 

Thread Starter

Tejasvi471

Joined Jun 9, 2020
14
Televisions and their remote controls have infrared-pass plastic windows in front of their sensors, sometimes in front of the emitters too. Canibalize them from defunct units and check if they work for you.
are they available in market, what do i call them, cause every time i search IR filter it gives me camera lenses
 

Thread Starter

Tejasvi471

Joined Jun 9, 2020
14
Sure, such filters are available. For a standard wavelength, here is an example: https://www.alluxa.com/optical-filter-catalog/ultra-narrow-bandpass/935-4-0-45-od5-ultra-narrow-bandpass.html Maybe you can get closer to the two wavelengths you want on $pecial order.

Why those particular wavelengths?

I would probably use coding to distinguish between the two sources.
this is too expensive at $2653, don't they make something less costly like a visible light colored glasses
 

jpanhalt

Joined Jan 18, 2008
9,420
Your original post wanted to distinguish between 920 nm and 940 nm using a "filter." That is a very narrow band width for ordinary filters. Moreover, any filter that can make that distinction clearly, will also attenuate the light intensity. The colored plastic for TV remotes comes no where near being that good. Finally, those are the "center" of the emission bands. Even if you paid $10,000 for narrow band filters, the width of the emission band would cause false detections.

That is why I would code my emitters and make the distinction based on the code. You won't even need to worry about ambient light. That is how TV remotes distinguish which button you press.
 

DickCappels

Joined Aug 21, 2008
6,386
I think jpanhalt is thinking way ahead on this. Using different codes from the transmitters will allow the receiver to distinguish between two or more. If it is desired to decode these signal independently but simultaneously in one receiver, that can be done by using psedonoise codes in the transmitter and combining them before transmitting.
 

SamR

Joined Mar 19, 2019
2,126
Your terminology is part of the problem. Optical Filters are used to remove wavelengths from light, not pass them. Why do you want to "filter out all frequencies but one coming out IR LED"? IR LEDs by design only emit IR frequencies in a narrow bandwidth?
 

Tonyr1084

Joined Sep 24, 2015
4,535
I'm leaning toward agreeing with @jpanhalt and @SamR on this. IR transmitters and sensors are not intended to discriminate between narrow bandwidth of the IR band. Rather, they send and receive a series of codes, depending on the intent. A TV remote may send a code (example 1011100100011111) to change to a specific channel (and I don't know the TV codes) while a different code (00010001000101100) changes the volume. The remote transmits these different codes and the TV reads them and responds accordingly. It's not filtering that does different things it's coding.

A more comprehensive description of what you want to accomplish will lend well to AAC members being able to guide and direct you to a successful project. One that doesn't cost tens of thousands of dollars.
 

Thread Starter

Tejasvi471

Joined Jun 9, 2020
14
Since members are asking for Project Details, Here is what I am Trying to achieve.
Its only a small module in my full project.

1's and 0's are hard wired, That is 1's mean no slit covering and 0's means slit is covered.

Hope it clears doubt, I am open to suggestions
 

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Thread Starter

Tejasvi471

Joined Jun 9, 2020
14
Your original post wanted to distinguish between 920 nm and 940 nm using a "filter." That is a very narrow band width for ordinary filters. Moreover, any filter that can make that distinction clearly, will also attenuate the light intensity. The colored plastic for TV remotes comes no where near being that good. Finally, those are the "center" of the emission bands. Even if you paid $10,000 for narrow band filters, the width of the emission band would cause false detections.

That is why I would code my emitters and make the distinction based on the code. You won't even need to worry about ambient light. That is how TV remotes distinguish which button you press.
Thanks for the detailed reply, What is the typical bandwidth for a normal cheap IR filter or band pass filter
 

jpanhalt

Joined Jan 18, 2008
9,420
Thanks for the detailed reply, What is the typical bandwidth for a normal cheap IR filter or band pass filter
Please tell us what you are trying to do. You seem to have had very little experience with spectroscopy and in particular infrared. I do not have time to go through every word with you.
 

Thread Starter

Tejasvi471

Joined Jun 9, 2020
14
Not familiar with these terms. Are you referring to highs and lows? Or are you attempting to achieve a digital signal with a mechanical encoder wheel?
yes kind of.
A mechanical slit when opened permits light to pass which is 1
A mechanical slit when closed restricts light which is 0
 
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