# Is a resistor needed for LEDs in this beatbox project? [duplicate]

I'm making a LED beatbox (seen on Kipkay.com). I'm using 8 LEDs (5 millimeters, I don't know if this helps) and my power source is 12 VDC 800 mA. Do I need to add a resistor? If yes, which one should I use?

• Yes, you will need resistors. See this earlier thread. To determine the value of the resistor, we need to know 2 things: voltage drop across the LED (forward voltage drop), current through the LED. Post this info, please. This info usually comes from the LED's datasheet. Also, are you going to light up all the LEDs at once, or one at a time, or in groups? Are all of the 8x LEDs the same (color, model)? Aug 1, 2013 at 3:26
• Aug 2, 2013 at 20:44

Yes you need a resister per LED. Assuming you want your LEDs to run at a current of about $I_f$ = 20mA current and your LEDs have a forward voltage of $V_f$ = 1.7V (this is a wild guess, check your datasheet), you'll want to size your resistors as follows:
$(12 - V_f) / (I_f) = R$
$P = I_f * I_f * R$