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to basically make an LED display on a cap. The thing is, I don't want to program anything, just light up a design, wired with a switch to turn on and off. Most instructions are how to program a display using a microcontroller and transisters, etc.

My plan is to use 3mm leds and just solder them together and power it with a 9V. Would that be feasible, wiring the LEDs in parallel strands.

Also, I know that I might want to use resisters to make sure the current isn't too high and burn out the bulbs but I'm not sure where to put them in the circuit or how to calculate it. (I can't make a circuit from looking at a schematic either)

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## 3 Replies

Magnetron (author)2014-02-02

this is a cicuit of a small led cube or so think so i thout it might help with your project good lug

iceng (author)2013-12-31
• You need to lay out only the lit LEDs.
• Assume 3.6V 20ma LEDs two at a time is 7.2V @ 20ma
• At 9V a resistor will drop 9 - 7.2 = 1.8 Volts
• R = V / I = 1.8 / 0.02 = 90 ohms
• P = V × I = 1.8 × 0.02 = 16 mw
• Assume 1/2 of the LEDs are lit = 128 LEDs =>> 64 groups of two
• Total current = 64 × .02 = 1.28 Amperes which  is a lot for a 9Volt Battery
•
• You may have to go to 18 Volts
•  Assume 3.6V 20ma LEDs four at a time is 14.4V @ 20
• At 18V a resistor will drop 18 - 14.4 = 3.6 Volts
• R = V / I = 3.6 / 0.02 = 165 ohms
• P = V × I = 3.6 × 0.02 = 72 mw
• Assume 1/2 of the LEDs are lit = 128 LEDs =>> 32 groups of four
• Total current = 32 × .02 = 0.64 Amperes which  is reasonable lot for a dual 9Volt Battery      .

mpilchfamily (author)2013-12-31

Then you don't need a matrix. Use an LED calc to find out the best wiring and resistors needed for your LEDs using your 9V source. Then Insert your LEDs in the pattern you want and your done. Just be sure to use wires between the LEDs so you have plenty of flexibility in placing your LEDs.