Luxeon modulation for morse code

Hello,

I want to modulate a Luxeon 3 Watt LED's output at roughly 600Hz for sending Morse code light signals via a Fresnel lens for free-space communications. I know that the 555 alone will not provide enough current to drive the 3W Luxeon. I am wondering if simply adding the output pulses from a 555 IC oscillator circuit to the Luxeon drive current would provide and adequate depth of modulation to be detectable by a PIN diode based amplifier. Has anyone done this? I have given up in frustration after multiple attempts at voice modulatio of a Luxeon so I need something really simple. Thanks for any help, Ed507

Check out This link and Google an old thread about Voice Comms.

Norm

Or if you can do any surface-mount soldering at all, you could check out the Texas Instruments app note "SLVA346" - TLC5916 One-Wire Control – Eliminating Microprocessor Control for LED Driver. I don't know what the current requirements for a Luxeon 3 Watt LED are (well, as a guess 3W would be a bit less than an Amp if Vf is a bit more than 3V?), this app note shows you how to drive a TLC5916 (or 5917, which I know can do about an Amp, or 5926, which can do about 2Amps) just using a 555 timer, but you could then drive the "enable" pin with your current 555 setup. Or you could maybe just use a 556 for both?

Surface mount soldering of an SOIC isn't too bad, you can do it with a hand soldering iron. The rest can be through-hole if you so desire.

You can get the extra current to drive the Luxeon by adding a bipolar transistor between the 555 and the LED. The configuration is the "emitter follower", where the drive signal (555 output) is connected to the base, the collector is connected to the supply voltage, and the emitter is connected to the load (the LED).

The basic circuit can be found described here:
http://hades.mech.northwestern.edu/index.php/Diodes_and_Transistors
just scroll down to the part labeled "Emitter Follower".

You'll need to pick a transistor with the proper ratings; i.e. the collector current must be greater than the desired LED current, the Vceo must be greater than the supply voltage, and.... try a package rated for at least a watt of power dissipation, just to be safe.

You'll probably want to add a resistor in series with the LED to limit the current to the desired level too.

Steve K.

Norm said:

Check out This link and Google an old thread about Voice Comms.

Norm

Click to expand...

Not sure what your intent is for modulation / demodulation, but if this is outdoors, visible light is not the best thing to use. There is a hole in the sunlight spectrum in and around 850nm. Using that wavelength of light (if your lens supports it) will increase your signal to noise ratio. Silicon photo detectors are still pretty efficient at this wavelength.

If you have any microcontroller experience, I would consider using a micro instead to pulse the diode as it will make control easier.

You may want to research IR remote control receiver ICs and communication using these. In this case, you modulate a signal in and around 30-50KHz normally and your data rides on top of that signal. It will give you a lot more signal to noise ratio.

I would not be surprised if you could not modify one of these receivers to take off the IR filter so that it works in the visible range if you want to stick with visible, however, like any sensor of this ilk, it will have only so much dynamic range and hence why it is good to use narrow bands of wavelengths and filter what you do not need.

Semiman