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 Post subject: Volt Question
PostPosted: 15.12.2002 02:26 
Hello all, this question may not be for the mouse mod. But its for that keyboard spot light mod. I have 2 LEDS both are 5mm blue intensity 2600mcd 3.7v 20ma. How is it possible to run them both if the power source(keyboard) has only 5v and both leds have 3.7v. And another question is why a resistor of 68ohm? If they say to add the (mA) of both leds then divide the total (mA) by the total voltage of both leds.

Example:
(20ma+20ma=40ma) (7.4v/0.04=185ohm)

And finally the last question. Were do I put the resistor. Next to the switch or next to the powersource +?

:) :) Thank you to much for ya help :) :)


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 Post subject:
PostPosted: 15.12.2002 03:17 
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Regular Modder
Regular Modder

Joined: 25.04.2002 10:06
Posts: 152
Location: Los Angeles, USA
Read through japala's tutorial here http://metku.net/index.html?sect=view&n ... /index_eng , this will give you a better understanding of what is going on. You can power both leds on a 5 volt source because you will run them in parallel. Think of it as using an extension cord with multiple outlets, more stuff to plug in on the same amount of power you just use more current. The 68 ohm resistor is correct. You can use this calculator over at bit-tech for future checks http://www.bit-tech.net/article/68/ . Then you can check the wattage. Your two leds give you .04 amps total. Your voltage difference is 5-3.7 = 1.3 volts. Multiply these two together and you get .052 watts, so here you would be fine with even the smaller/cheaper resistors that are .25 watts although the .5 watts might be a little easier for you to work with. Your choice. The resistor can be placed anywhere as long as it is between your power source + and the positive(anode) end of the led.


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