buying advice shift registers

Forum 2005-2010 (read only) General Frequently-Asked Questions
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So I calculated: 5V - 3.5 (led voltage) / 0.02 = 75 ohms

I believe the mistake he was making was to use the full 5 V in the power calculation rather than the voltage drop across the resistor. This leads to:

P = V^2 / R = 25 / 75 = 0.3333

  • Ben