Infared Transmitter

LEDs have a viewing angle specification that tells how directional they are.

Bob

 

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
Adam

 

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.

Read about remote controls on google.

It is typically not as simple, in most applicatipns, as turning the IR transmitter on and off, some form of carrier frequency has to be used.