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Step 3PREPARE THE POWER SUPPLY
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I used a 4.5 volt wall wart transformer to power my nightlight. You can buy a power supply or maybe you have an old charger that went to a cell phone that died long ago. Whatever power supply you use, make sure the output is direct current (DC) and not alternating current (AC). The output voltage is not really too critical so long as it is in the 3 to 9 volt range. You can always adjust the resistors for whatever voltage you have. See my note below to figure out what value of resistor you need to use.
I used a plug and jack with my power supply, but you could just solder your power wires directly to the LEDs and resistors. This thing uses very little electricity so a switch isn't necessary.
NOTE: To determine the resistor value you will need you need to know the power supply voltage. It should be clearly marked on the power supply. As an example, suppose your power supply puts out 6.0 volts. Just divide 6 by 0.03 (30mA) which is the maximum current the LEDs can take. This value should be the same for any UV LEDs you buy. Doing the math gives you 200. Go to Radio Shack or your junk box and find a resistor that is 200 ohms or greater. I won't matter if it is a bit larger than the number you came up with. In this case a 220 ohm resistor will work fine. Just don't use a resistor with a value less than what you calculated (in this case 200). If you do go lower, your project may still work, but the LEDs will slowly loose their UV qualities and your nightlight won't glow as brightly.
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I used a 4.5 volt wall wart transformer to power my nightlight. You can buy a power supply or maybe you have an old charger that went to a cell phone that died long ago. Whatever power supply you use, make sure the output is direct current (DC) and not alternating current (AC). The output voltage is not really too critical so long as it is in the 3 to 9 volt range. You can always adjust the resistors for whatever voltage you have. See my note below to figure out what value of resistor you need to use.
I used a plug and jack with my power supply, but you could just solder your power wires directly to the LEDs and resistors. This thing uses very little electricity so a switch isn't necessary.
NOTE: To determine the resistor value you will need you need to know the power supply voltage. It should be clearly marked on the power supply. As an example, suppose your power supply puts out 6.0 volts. Just divide 6 by 0.03 (30mA) which is the maximum current the LEDs can take. This value should be the same for any UV LEDs you buy. Doing the math gives you 200. Go to Radio Shack or your junk box and find a resistor that is 200 ohms or greater. I won't matter if it is a bit larger than the number you came up with. In this case a 220 ohm resistor will work fine. Just don't use a resistor with a value less than what you calculated (in this case 200). If you do go lower, your project may still work, but the LEDs will slowly loose their UV qualities and your nightlight won't glow as brightly.
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