# Infared Transmitter

Discussion in 'General Electronics Discussion' started by Elgato72, Jan 21, 2014.

1. ### Elgato72

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Jan 21, 2014
Hi,

I have a project idea involving infared signals. I need to send a infared signal in a general direction, much like laser tag. I have found infared transmitters online, but I need to make it go in a direction, so I am not sure what to purchase and do to accomplish my goal. Anyone have any ideas?

Thanks,
Elgato72

2. ### davennModerator

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Sep 5, 2009
welcome to the forums

you will need a lens or 2 to focus it

Dave

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Jan 21, 2014
Thanks a ton

4. ### Elgato72

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Jan 21, 2014
Do you know where I can find these lenses?

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Most IR transmitters will use a laser (highly directional) or a LED (quite directional).

How do these not solve your problem (i.e. you point them in the direction you want).

If you need to focus the beam, you can place a lens in front of an IR LED. Clearly you can't see the light, so you need to rely on the signal strength or use a camera which can see IR (many digital cameras can) to determine when you have it focussed sufficiently.

edit: well that was far too late.

Last edited: Jan 21, 2014
6. ### Elgato72

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Jan 21, 2014
Oh, I thought that they went in all directions, buy the looks of the LED. Thanks a lot.

7. ### BobK

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Jan 5, 2010
LEDs have a viewing angle specification that tells how directional they are.

Bob

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Dec 18, 2013
It would be nice if LEDs emitted light as a pure cone within their half power angle but they don't. They produce quite a bit of fuzz around the edges. To roughly work out the angle you need is you take the radiant flux of the LED divided by the solid angle of the cone which is sr=2*pi(1-cos(angle/2). So you can see as the angle is reduced you will need less power to produce the same irradiance (only on a surface much smaller than the area that the cone would produce irradiating on a surface.
This will give you the intensity in mW/sr (Steradians). You then use the irradiance specification of the receiver in mW/cm^ to find out the current that will be produced by the receiver for a given distance then you can work out your led angle.
hope this helps

9. ### Elgato72

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Jan 21, 2014
Ok, great, thanks.

10. ### Elgato72

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Jan 21, 2014
Where online can I find a lens?

11. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
eBay or any of the cheap Chinese sites will have plenty.

12. ### shumifan50

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Jan 16, 2014
IR transmitters have a very short range so require a bit of manipulation to achieve any significant distance, as used in remote controls. Gaining distance is achieved (typically) by overdriving the LED transmitter in short busts, allowing it to cool down in between so it does not burn out. Using a lens will also gain some distance, but it will depend how far your receiver is away from the transmitter. Furthermore, you have to be aware that normal light has an IR component and you have to filter this out to achieve a reliable signal.

If you use the above way (pulsing) of increasing the IR transmission, you can get away without a lens and merely enclose the transmitter in a box with a pinhole through which you focus the IR light - this can make it very directional.

Note that the best way to achieve IR distance is to use a micro controller (like a PIC) to drive the transmitter and use a MC to receive as well, although it can be achieved with discrete components. There are specifications for IR remote controls on the web.