ok i want to make an LED belt with about 60 LEDs. i will probally wire them in a series but not wure how to do it with a 9v battery. now it is on a belt so i really cant use more than a 9v battery. i am not sure about any resistors i know almost nothing about LEDs and the power they need. i diagram would be helpful.Here is the link to the LEDs ( 20 red diffused and 40 blue diffused. thanks in advanced
you need the Vf of each type. If you don't have it, look on line for the specs of a similar unit.
Then see how many you can put in a series string so that they add up to about 6-7 volts. For example, if Vf is 2.1 volts, you can put 3 in series, which adds up to 6.3 volts. That leaves 2.7 volts for the resistor. You calculate the value of the resistor as R = 2.7/IF, where IF is typical forward current from the spec sheet. If IF is 20 ma in this example, R = 2.7/0.02 = 135 ohms (use 150 ohms)
Now you repeat this string as many times as you want, putting each string in parallel across the 9v battery.
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