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LED Resistor Selector DialAuthor
Giorgos Lazaridis
December 14, 2012

PAGE 3 of 3 - How to use the LED Resistor Selector Dial

How to use the LED Resistor Selector Dial

You can hold the selector with one hand from the rectangular piece that extends on the left side of the fixed circle. With your other hand you can hold and rotate the rotating wheel:


The fixed wheel (the smaller one) has the LED voltage. The rotating wheel (the larger one) has the supply voltage. You wanna match now the supply voltage with the LED voltage by rotating the bigger wheel. For example, if the supply voltage is 5 volts and the LED voltage is 2.2 volts (typical for red LED), this is how you should align the wheels:


You are now ready to get the resistor value. From the "Resistor Value" window you can read the value for 3 different current rates: 10, 20 and 30mA:


As you can see, for 20mA current you should select a resistor around 140 Ohms...

Finally, flip to the other side to read the power that needs to be dissipated on the resistor:


The power is between 55 and 60 mWatts..

More LEDs in series???
What if you want to use one resistor for 5 LEDs in series? How can you use this tool to calculate the resistor value? Simply, add all the forward voltages of the LEDs and use this value instead. If for example you want to connect 5 cool white LEDs in series and each LED has forward voltage 3.3 volts, then the total forward voltage will be:

Vf_total = 5 x 3.3 = 16.5 Volts

Now, if the supply voltage is for example 22 volts and you want to allow 30 mA of current ...

22 power supply aligned with the 16.5 volts required for the 5 LEDs in series For 30mA, the proper resistor is 180 Ohms 170 mWatts is approximately the power that needs to be dissipated on the resistor

Continue reading. Click here to go back to the first page <<<.
 OR click here to view the presentation.



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  • At 16 January 2013, 15:36:19 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @AAVV corel draw

  • At 16 January 2013, 8:23:50 user AAVV wrote:   [reply @ AAVV]


  • At 15 January 2013, 6:02:24 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @Mark Wops!!! Thanks!

  • At 15 January 2013, 0:39:25 user Mark wrote:   [reply @ Mark]
    • fantastic. one slight error on page 2 "As you can see, for 20mA current you should select a resistor around 140 mA... " shouldn't that be ohms :)

  • At 14 January 2013, 23:32:56 user Jeff wrote:   [reply @ Jeff]
    • This is genius! I love it, will definitely come in handy! I may laser etch a version in acrylic, if so I'll send you one!

  • At 8 January 2013, 18:45:05 user N!ck_modmag.net wrote:   [reply @ N!ck_modmag.net]
    • Awesome job! Featured this project on our website - http://en.modmag.net/news/led-resistor-selector-dial-by-giorgos-lazaridis

  • At 15 December 2012, 21:40:19 user Panagiotis Kalogeris wrote:   [reply @ Panagiotis Kalogeris]
    • A-W-E-S-O-M-E....!!!!!!!!!!!!!!!!

    reddit this Reddit this

     HOT in heaven!

    NEW in heaven!

    New Theory: AC electric motor working principle

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