protofuse Posted July 6, 2009 Report Share Posted July 6, 2009 hi experts,before to finish soldering my DOUTx4 modules w/ ULN to drive my rgb matrixes, I have to choose resistors values.The rgb leds I got are those : http://www.sparkfun.com/datasheets/Components/YSL-R596CR3G4B5C-C10.pdfVred = 2VVgreen= 3.2VVblue= 3.2Vall for I=20mAsoI guess:Rred = 100 ohmsRgreen = 160 ohmsRblue = 160 ohmsam I right ??the fact I use ULN, the fact I use DOUT modules would alter these values ???I guess, no.But I'd prefer to ask before, if anyone has experiences with thatall the best,protofuse Quote Link to comment Share on other sites More sharing options...
lylehaze Posted July 6, 2009 Report Share Posted July 6, 2009 Hmm, I think 150, 100, 100 looks closer.Try this website:http://led.linear1.org/1led.wizFor a quick first run, Source Voltage is 5, Diode forward voltages and currents you already provided.This will provide safe resistor values that can be left on forever without damaging the LEDs.So what can change the numbers? The DOUTs that supplies power may have a slight voltage drop. You could figure that out and deduct it from 5V. The ULN outputs may not QUITE get all the way to ground, you could deduct that from the 5V also. In truth, neither of those will be enough to make a difference.LEDs that are being scanned in a matrix CAN be overdriven for bit more light, but it will shorten the life of the LEDs, and if the scanning ever stops unexpectedly, the LEDs will be unhappy.Have Fun,LyleHaze Quote Link to comment Share on other sites More sharing options...
protofuse Posted July 6, 2009 Author Report Share Posted July 6, 2009 thanks a lot lylehaze.it will be a common cathode led matrix.I did the calculation: 150, 100, 100 seems to be fine indeed!I'll buy my resistors :) thanks a lot! Quote Link to comment Share on other sites More sharing options...
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