Infrared transmitter

Discussion in 'Electronic Design' started by Paul Horwood, Apr 26, 2005.

1. Paul HorwoodGuest

I wonder if anyone can help me?

I am looking at building a 6 band infrared transmitter.
Now it seems that most infrared beams are modulated via a high signal like
37Khz.

What I want to do is to transmit all the 6 bands at once but on different
infrared frequencies.
The frequencies would be for example:- 935,5 - 937,8 - 927,2 - 948,1 -
934,2 - 928,3 nm (nanometer) .

How can this be done?

Is there a meter that can be used to determin the frequency of infrared
light?

Or is there a calculation that can be done to determin which components I
would need?

Will the standard infrared emitters be capable of narrowed bandwidth like
this?

Paul...

2. OBonesGuest

This is not frequency, this is wavelength.

Well, I guess any oscillating system could do. The problem might be with
the emitter and receiver that might not be able to switch at the desired
speed. Find the frequency and check the datasheets.

The frequency of the light itself is a parameter of the emitter,
indicated in the datasheet. The frequency of "on-off" switching depends
signal into electricity, then use an oscilloscope to "see" that on-off
switching.

Decide which oscillating circuit to use first

Bandwitdh is not directly impacted here, it also depends on the coding
you use on top of your frequency. Which one(s) do you plan to use?
Frequency modulation, amplitude modulation, phase modulation?

Cheers

3. Paul HorwoodGuest

Whoops.. so it is.... )

ok, looking at amplitude modulation for 29Khz,32Khz,29Khz etc..

I am not sure though if I need the infrared Wavelength varied.. On the
details for this transmitter it states:-
" infrared sender radiating six different frequencies in the infrared range
"

This is why I asked the above questions...

Paul...

4. OBonesGuest

No, you don't need the infrared wavelength to vary that's way too
complicated. What you do is vary the frequency at which you turn on,
turn off the light. The color of the light doesn't matter (well, not for
this parameter), it's the frequency at which it goes on and off.
Infrared is just "better" because it travels well in broad day light
So what you will do is this:

On-Off-On-On-Off-Off-Off-On

and so on. Or if you do amplitude modulation, it could be:

Full-Half-None-None-Half-Half-Full

The frequency at which you send the states is the frequency that you
have to look at. If the emitter is blue, red, green, infrared,
ultraviolet, it does not matter, it does not impact on your driving circuit.

What you need to look at in the datasheet is how fast the emitter and
receiver can change their state and how sensitive they are. If for
instance it takes 1ms for the receiver to go from fully off to fully on,
then you can't send anything more frequently than every 1.1ms (security
margin of .1) and that's a 1/1.1e-3 = 900 Hz
That value here is just an example, I would hope the receiver is much
better than this.

5. Guest

You *can* do this, but the cost would be quite high. Most
semiconductor emitters are not single frequency, but put out a gaussian
distribution over a hundred or so nm. You could use a monochromater to
get to a very narrow band or single frequency. You would use an
emitter/monochromater for each channel on the transmitter and a
monochromater/detecter for each channel on the receiver.
You say you want to do 6 channels "at once". Do you really need to do
this, or is there a modulation scheme you can use (like time-domain
modulation)? What is the data rate you need to transmit?