Those were the only one's I could find capable of producing the range of acceptable wavelengths (roughly 660 nm up to just short of near infrared). Power supply current limit is basically 20-30 ma. LED will essentially provide three functions: transmission, detection, and illumination. The first two will require very little current to operate, the illumination will consume the vast majority of the circuit's power.



Okay, thanks, that's a relief to hear. I can just experiment with the frequency setting, but do you off chance happen to have any idea what sort of frequencies we're talking about here? I realize of course that it may be different for various wavelengths, but a ball park guess might be helpful in any case.

Adicore has what appears to me to be an extremely long selection of bandwith 20 ma leds. Are you sure you can't find low power ones that fit your needs? I find Adicore to be quick to ship and low in price.

 

There is also no reason you cannot operate upur 350mA LEDs at 20 mA. In my experience, they will actually be brighter than a 20 mA LED at the same current.

The circuit is much simpler, just a series resistor, but you would have to experiment to get the value since the datasheet probably does not give you the forward voltage at 20mA.

Bob

 

Consider: typically an LED is 50% efficient. A 350mA LED (I guess this is red?) will operate at 2v or 660mW. 330mW is a lot of light. Consider, the old 100W tungsten lamps we all liked until we were told we could not have any any more were about 10% efficient, or 10W of light power, so the LED is equivalent to a 3W lamp. Torch bulbs e.g. 6V 60mA dissipate 360mW and maybe give out only 30mW of light. That is pretty visible, and as LEDs are small the intensity is quite high. Quite often the problem with LEDS is dimming them to 1% or less. I agree with previous comments that most (good) LEDs will run at lower currents than the maximum. Seems that the problem was that early LEDs were not particularly uniform and would show dark spots if run at lower currents, but new LEDs typically are better.