How do i measure light frequency?

In summary, the author of the article suggests that the problem with the screens is that they emit IR impulses at the same frequency as the remote controls. If you can find a receiver or remote that is not affected by these impulses, the problem will be solved.
  • #1
trevorjdaniel
6
0
Hi There!

I have a bit of a problem...

I work in Audio Visual and install video matrix systems.

We are findind that the newer LCD screens are throwing out so much IR interference that they are blocking the Remote Controls from operating the Sky Boxes...

The manufacturer of the matrix panel have introduced new "shielded" IR receivers but this has not helped the problems.

So, my question is...

Firstly, how do i go into a room and measure the frequency of the IR coming out of the TV and how would i do the same to the Remote Control?

The reason I ask this question is because I am wondering if it would be possible for the manufacturer to "remove" the unwanted IR from the system and just leave the SKY IR signals.

My thoughts are this would be possible AS LONG AS the IR coming out of the screen is not on the same frequency as the Remote Control is transmitting...

Sorry if there are flaws in my theory but i am not a scientist. just need some help on IR and light frequency - i think - lol

Thanks

Trev
 
Science news on Phys.org
  • #2
I think you will have a problem with the appropriate devices. Sorry.

----

Just one thing: I don't think its the actual frequency of the IR causing this problem but its rather the IR impulses emmitted from the screen causing the problem. An IR remote works by conveying certain patterns of impulses to the target. A constant overlay over the beam of a IR-source with the same frequency would not effect that as long as its not to strong. Its rather that the IR-impulses from the Screen mix with the pattern from the remote.

[Edited]
 
Last edited:
  • #3
thanks for the reply...

so, i need to get a prism and put it in front of the tv and then get a night camera and look at the light coming out of the prism through the camera?

what would i expect to see? how do i then measure it?

thanks

trev
 
  • #4
ah, i see, i think...

that would make it quite problematic/difficult to "scrub" then and remove the unwanted pulses would you think?

any thoughts on a solution?

trev
 
  • #5
I've found an interesting article on "How Remote Controls Work".

On page 2 of the article it mentions that "To avoid interference caused by other sources of infrared light, the infrared receiver on a TV only responds to a particular wavelength of infrared light, usually 980 nanometers."

Article is at http://electronics.howstuffworks.com/remote-control1.htm

Does this mean that if everything except 980 nanometers was filtered out it would solve the problem or is it still liable to have "overlay" pulses from the screen?

Trev
 
  • #6
In reply to #4

This heavily depends. But from what you ask I don't think you are a professional at tweaking circuit boards and electronic components?

Logically there will only be a few possible solutions:

  • Arrage the screen and the sensor the way the sesor doesn't receive any (major) impulses from the screen (shield it correctly)
  • Tweak the circuit so it will not react to the length of impulses emitted by the screen. Imagine conveying a morsecode standing next to a flashing beacon. Now make the morse signals longer so they can be told apart from the beacons
  • Increase the amplitude and decrease the sensitivity for the remote and the receiver respectively so it will not react to the screen IR any longer

All this you better double check. I'm not an engineer either. I'm just giving my best to assist you with what I know.
 
Last edited:
  • #7
In reply to #5

If the the article is correct (which I presume) you were right with what you assumed before. That the screen actually matches the frequency of the SAT exactly. This discloses another option for fixing it.
If you manage to change the receivers and the remote frequency to one which is not present elsewise (this means change it from 980nm to something else), you will not sustain any interferences any longer.

Actually I think that's the most convenient way to do it. I think doing so is the very easiest to do. Just know how. Maybe your TV/screen ships with a circuit scheme explained in the manual. I know some TV's which do come with a detailled explanation of their interior.

With respects to "filtering 980nm" out: Of course it would also fix it if you could filter out the range of frequencies (like from 970 to 990 or something like that) at the screen itsself. But I doubt that this is possible without covering the monitor with something which one can hardly see thru. I don't even know what it would be called. I know IR-Filters but those do just the opposite.

Well, maybe "inverse-IR-filters" are fully transparent (which would make sense assuming that they really only filter out IR and no visible light) and you find one for 980nm. Good luck.
 
Last edited:
  • #8
what about using an infrared camera to see the IR coming from the TV and the remote when it is being used?
 
  • #9
hi Tshock

thanks for the reply.

i need to know if the light sources are overlapping and interfering with the ir. with the suggestion you have made I am not sure i'd be able to do this...

do i need a spectrum analyser i wonder?

trev
 
  • #10
Look, I don't understand where this is ment ot be going. You know the screen interferes with the remote, don't you? So you can certainly assume that they are on the same wavelength. Now why do you want to analze it further? Is'nt it enough to know what's wrong and how to fix it, but do really need to put your hands on the fault and touch it?
 
  • #11
Glass is opaque to IR, but I'm not sure about this case. You could try placing the screens behind glass and testing to see if there is still interference.

Remember that just because something is transparent to visible light does not mean it is transparent to IR, and similarly, if it is opaque to visible light, it is not necessarily opaque to IR.
 
  • #12
dst said:
if it is opaque to visible light, it is not necessarily opaque to IR.

Though this is hypotetically possible I'd like you to name a material which meets this, because I can't think of anything usual. Or I just appear not to know one which is common.

Putting glass in between is actually a good idea. I didn't think of glass as an IR absorbing material.
 
  • #13
ManDay said:
Look, I don't understand where this is ment ot be going. You know the screen interferes with the remote, don't you? So you can certainly assume that they are on the same wavelength. Now why do you want to analze it further? Is'nt it enough to know what's wrong and how to fix it, but do really need to put your hands on the fault and touch it?

Hi ManDay,

I think you are right. by assumption. that must be the answer.

This thread doesn't make sense out of context really...

maybe this thread throws more light on the subject... exscuse the pun...

this is the background of my newly born interest in IR...

http://www.remotecentral.com/cgi-bin/mboard/rc-custom/thread.cgi?14910

trev
 
  • #14
Trevorjdaniel;

Your only real option in terms of measuring the wavelength of the IR radiation is using an optical spectrum analyser, which unfortunately is not cheap.

The manufacturers should have extensive data on the emission characteristics of their screens, see if you can find details of the emission spectrum, specifically the portion that overlaps with the spectral bandwidth of the remote control.

ManDay said:
Though this is hypotetically possible I'd like you to name a material which meets this, because I can't think of anything usual. Or I just appear not to know one which is common.

Putting glass in between is actually a good idea. I didn't think of glass as an IR absorbing material.
Silicon is probably the most common material I can think of that is opaque in the visible and transmits IR. Chalcogenide glass also has these properties.

Also, silica glasses do not absorb near IR radiation, only the mid-far IR from wavelengths of about 2-3 microns and above. There are probably other glasses whose wavelength cut-offs are closer to the visible, but are less common, and consequently, I can't recall their names :redface:.

Claude.
 
Last edited:
  • #15
Semiconductor infrared detectors are not very frequency sensitive. The photons of radiation of room temperature objects do not have enough energy to give the electrons in the detector enough energy to get across the band gap to the conduction band, but higher frequencies such as visible light will still produce a signal in the detector.
All Infrared communications use an infrared source which is switched on and off with an intermediate frequency, roughly 100 Khz for remote controls, higher for faster communication. The resulting IR, amplitude modulated by an intermediate frequency is then switched on and off much slower to get the signals of the remote across.
The resulting signal can be picked up by a receiver with a phase locked loop, that isn't very sensitive to which intermediate frequency it picks up, because 100 Khz modulated IR doesn't occur in nature.
I think the problem occurs because the backlight of the LCD panel is run of a switched power supply that produces flicker at a frequency that the infrared receiver picks up. The exact frequency of visible and near-infrared light that is sent out isn't relevant.
 

What is light frequency and why is it important to measure?

Light frequency is the number of oscillations or cycles of an electromagnetic wave per unit of time. It is important to measure because it determines the color and energy of light, and is used in various scientific and technological applications.

What unit is used to measure light frequency?

Light frequency is measured in Hertz (Hz), which represents the number of cycles of an electromagnetic wave per second.

How do I measure light frequency with a spectrometer?

A spectrometer is a device that can measure the intensity of light at different wavelengths. By analyzing the spectrum of light, you can determine its frequency using the formula: frequency = speed of light / wavelength.

Can I measure light frequency without expensive equipment?

Yes, you can measure light frequency using a simple homemade device called a light-to-frequency converter. This consists of a light-sensitive resistor and a microcontroller that can measure the frequency of the electrical signal produced by the resistor in response to light.

Is there a difference between light frequency and light wavelength?

Yes, light frequency and wavelength are related but different properties of light. Frequency is a measure of how often an electromagnetic wave oscillates, while wavelength is the distance between two consecutive wave peaks. They are inversely proportional, meaning that as frequency increases, wavelength decreases and vice versa.

Similar threads

Replies
3
Views
683
Replies
3
Views
1K
  • Atomic and Condensed Matter
Replies
4
Views
942
Replies
19
Views
1K
Replies
16
Views
724
Replies
40
Views
2K
Replies
2
Views
607
Replies
3
Views
1K
Replies
7
Views
844
Replies
9
Views
1K
Back
Top