Tuesday, 25 February 2014

USB Powered LED

For a bit of fun, I was looking at reusing some old USB devices. I had an old USB mouse that was past its use-by date, so I pulled it apart and did some harvesting of components.

One of the things that I was left with was the USB cable.

The cable had 4 wires and a shield. The white and green wires are Data (positive and negative) and the black and red wires are power (red = positive, black = ground). I did a bit of trimming (cut off the shield and the white and green wires) and then crimped the red and black into a DuPont 2 pin female housing.

Picture 1

I then attached some jumper wires to the DuPont so that I could connect it up to the prototype board.

Next, I made up a prototype board with some 3mm LED (8x red and 1x green), some jumpers and some 220 ohm resistors in parallel.

Picture 3

This is a pretty simple circuit, nothing fancy, just some LED in parallel and some resistors.

The positive is going to connect at the top and the negative is going to connect at the bottom.

Picture 5

I connected the jumpers from the USB to the prototype board and got ready to connect the USB to my computer. I have an AC/USB adaptor that I could use just as easily … but my computer is on and ready to rock … so, why not?

Picture 6

You can see the light thrown by the green LED in the back … it’s a lot brighter than the red LED. The red LED are about 5000mcd whereas the green is 15000mcd … so understandably brighter.

After looking up USB wiring on the Interweb, I found that the USB cable is (at 3m length) 5.1 volts according to my multimeter. Check out Pinouts R Us for more details about the voltage, wiring arrangement and such.

I guess that this would make a pretty simple power source for my electronics desk (for stuff that needs < 5VCC.

Anyway, I hope that this gives you some ideas … it has my mind going!

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