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ezrafitch1990
01-29-2011, 08:11 PM
my friend wants me to build a sign for them with lights so they can bring it to a bball game, i figure 8 LED's around the perimeter of the sign wuld work.

thinkin of using these:
http://www.radioshack.com/product/index.jsp?productId=3111495
these lights need 20mA of current and between 3.2-3.8 volts.


i drew it up in multi-sim and hooked the lights up all in parallel, and set the lights to 20mA and 3.2V. the multisim lights have an unchangeable resistance of 160ohms, and i was thinking of powering the circuit with a 9V battery. I did the calculations and figured I would need a 48.333 ohm resistor but used the 48.7ohm:
http://i52.tinypic.com/2hp51ms.png


My questions:
What size resistor would I need? (wattage)
How would I ground the circuit if my friend is going to be holding the sign up?
How long would the 9V battery last? Should I connect another battery?

of course ill change the resistor size but i dont know the actual resistance of the LED im gonna buy ill measure that lata

577trex
01-29-2011, 10:17 PM
-You don't need to actually ground the circuit.
-If this is just a one time use kind of thing, you can get away with using a 1/2 watt resistor.
-A typical 9v alkaline battery is good for ~600 milliamp-hours. So if you are using 8 lights each drawing 20 mA, the battery should be good for close to 4 hours.

ezrafitch1990
01-30-2011, 05:35 AM
-You don't need to actually ground the circuit.
-If this is just a one time use kind of thing, you can get away with using a 1/2 watt resistor.
-A typical 9v alkaline battery is good for ~600 milliamp-hours. So if you are using 8 lights each drawing 20 mA, the battery should be good for close to 4 hours.

repped, thanks