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Originally Posted by Kevin Watson
OH CR...UD! Mea Culpa, Dude. I'm sorry, you were correct and I laid down a healthy dose of... Er,... Well, you know. Anyway, the LEDs should be okay (I've driven them up to 800mA with the beacon waveforms), but now I'm somewhat worried about the power rating on the resistors. Some teams got 1/2 watt, but as I found out a few days ago, others got 1/4 watt (ouch!). I guess I'll add an entry to the FAQ addressing the resistors (which may be another good, but unintended, source of infrared energy  ).
-Kevin |
Kevin,
retraction appreciated, Thanks
There should be no problem with 1/4 W resistors
pulsed 40kHz & 1-2mS burst
(5% overall duty 1mS 40 pulses 50-50 & 10% 2mS 80 pulses)
WC .2A^2*.1duty*33 = .132W ~53% utilization of quarter Watt resistor.
at least not until they are accidently driven w/DC. (EDU pgm croak)
.2A^2*1duty*33 = 1.32W ~5X that quarter Watt resistor
that unmistakable smell of carbon burning, ahhh
that makes my proposed 4x LED series string + 1 current limit resistor
(or 2 junct tran+resistor regulator)
(5.36v from 7-8 Vbatt) look a bit better. least on paper.
We'll have to deal with the IR dropoff with dwindling battery supply,
or use an AC adapter, not a big deal.