A Cree LED in my linear current LED Transmitter

June 15, 2011 | Amateur Radio, electronics | By: Mark VandeWettering

I was away all weekend, so I didn’t get a chance to check out my LEDs that I got from Deal Extreme last week. Tonight, I just soldered a couple of clip leads and tried it out when hooked to the linear current modulator that I built (and blogged about) before. The transmitter in this video is set to pull an average of about 10ma average through the diode, with a peak of 20ma. That’s hardly enough to really get the cree going at all (I believe this one can go all the way to 350ma or so, and about 1W of output power) but it was enough to play with.



After I filmed this, I changed the current limiting resistor from 100 ohms to 16 ohms (by ganging two 32 ohm resistors together) and wired my multimeter in series with the supply to measure the power, and as expected it was 60ma, for an output of around 150mw or so (I didn’t measure the voltage drop, but I think it’s around 2.6 volts). It was quite a bit brighter, and was detectable even without any optical assistance at the other side of my room. To go much higher, I think I should probably swap the 2N3904 that I’m using to modulate it with something a bit beefier (like the IRF510s that I have lying around) and I’ll need some 1/2 watt current limiting resistors (probably around 3 ohms).

I’ll play with this some more in the next few weeks.

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