Thursday, November 17, 2011

First Hack - The LED Strip

Finally finished my first hack.

I needed a light for my kitchen counter, so I ordered a LED Strip from eBay and hacked an AC adapter to include an ON / OFF button and to connect it to mains without using a power socket.

So here's the theoretical work:

To cover the surface of my counter I used 48 segments of the LED strip (about 2 meters). Each segment has 3 white SMD leds (type 3528) and a 150 Ohm resistor. For it to work it needs a 12V power source with sufficient current output.
After learning from [ladyada] about these strips I figured that the theoretical current each segment needs to function at it's maximum is 16 mA. That is:
12V total - (3 leds * 3.2V) / 150R = 0.016A

For the total 48 segments that's 768 mA, resulting in under 10W lighting!!!
For that I bought a SMPS AC adapter in order to guarantee the regulated 12V while using that much current. An average (unregulated) AC adapter wouldn't provide nor the 12V neither near the maximum 1A stated. [ladyada] also shed me some lights on that matter.

White LED StripSuitable AC AdapterThe best switch button I could find

For the practical work:

As you will see for yourself, the tools weren't exactly the best suited for the job: a kitchen knife to cut, a soldering iron to remove plastic, a hammer and a nail to open holes...

The innards of a power outletMains power derivationAdhesive cable duct

In order to cut the space for the switch button in the AC adapter, my kitchen knife wasn't enough, so I used my soldering iron to heat a metal needle and a kind of a thick clip used by stores to keep shirts folded in it's package. Even so it was a hard work.

Pierced top cover from the AC AdapterCreating the space for the switch buttonThe working conditions

Then I just needed to solder the switch button and the wire to the board and cover it all with electrical tape.

The final cutConnecting the switch buttonThat's a wrap

And there we have it!
Our working LED Strip!

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