Projects/Create a nightlight from old usb charger
So everyone has a bunch of USB chargers lying around. This is a simple way to make a simple nightlight with only a few parts.
- USB charger
- USB cable
- white LED
- Find a white LED, and note the forward voltage (VF) and max forward current (IF-max)
- if you don't know the voltage and current, you can try VF=3.5V, and IF-max=20mA, and see if it's bright enough
- Calculate needed resistor
- R = (5-VF)/IF-max
- select the closest available resistor
- Cut and strip the usb cable
- Solder the components together in the following order
- USB's red wire -> resistor(R) -> LED(+) -> LED(-) -> USB's black wire
- LED positive lead is the longer, negative lead is on the side of the LED with the sightly flat side on the bottom
- You can just twist the wires and leads together, instead of soldering, just be sure they won't come apart, and insulate them well.
- Insulate the wire and solder joints
- Heat shrink tube works best
- Electrical tape is OK, but can shift over time
- You can let the led dangle from the charger, or put it in a clear/translucent cap or cover
- remember LEDs are very unidirectional so point the LED towards the ground or the direction that works best for you.
- you can add a darkness detector by adding a transistor(NPN BJT) and light-dependent resistor(LDR), but the LED/ON power usage is around 0.1W, so I didn't see the point.
- total power usage for my adapter was 0.4W