12VAC Power Supply from Ikea Wall Wart Light Power Supply

I recently rebuilt the lighting in my office because the crappy 12-volt strung lighting from Ikea that the previous owner installed was insufficient for working comfortably in my Man Cave™. Here's the NEW lighting above the sound-proffed barn door window shade things: New Man Cave™ Lighting

With the intensity of the photo cranked down a bit, you can see the simple valence I made out of pre-primered pine trim board:

Valence around new Man Cave™ lighting

The old lighting was 12VAC wire cable lighting with halogen lights. You seem the at Ikea. Two steel cable strung between two walls and the halogen lights hang between the wires at regular intervals. It's really cool, but it isn't very bright and the light is very yellow. I like daylight-ish fluorescent lighting, so that's what I bought to replace the old stuff.

Now, on to the real story: I salvaged the wall wart transformer/power supply for the 12VAC lighting and made a simple 12VAC power supply out of it. Not sure what I'll use that for, yet, but it was fun and I feel like I saved the landfill from containing weird metal and plastic parts.

I removed the pushbutton fuse reset thing and replaced it with a neon lamp power switch with a fuse reset feature and then cut a notch in the base of it to hold a strain-relief thing for a power cable from an old VCR I torn down. Then I put a wood base on the back and screwed in to together and sanded it for a nice finish. I haven't painted the edges black, yet. I also need to put little rubber footies on it to keep it from sliding around on the glass top of my electronics workbench.

Here are the photos:

12VAC transformer power supply

Completed power supply with power cord and switch.

Poplar Wood Bottom

Bottom is screwed into four holes built into case of wall wart. I wrote the specifications from the sticker on the transformer inside so that I would not forget how this could catch fire or trip a fuse.

Fuse reset button replaced with on/off/reset switch

I realized after I put it all together and tested the power that the replacement power switch might not trip at the same power draw as the old pushbutton. So, when I laid a big piece of copper wire across the terminals, it sparked and never did trip the switch OR the circuit breaker for the garage workbench. That's probably a fire hazard, but I'll usually have a good quality surge strip (or two) AND a house circuit breaker between my mishaps and the neighborhood power lines.

Update: LED Reading Lamp Materializing

For those of you with short attention spans, like me, here is a quick and lame video I threw together in iMovie:

I am building this for the new awesome bed I will be building this winter for our bedroom. There will be two of these lamps, one for me and one for my wife on either side of the headboard. The LED head will have a metal (or whatever I end up finding) shroud on it to keep light pollution down to a dull roar for the other person who might be sleeping.

The previous post showed the traces for the printed circuit board I made. Here is a photo of the board with the six surface-mount triple-LED packages soldered into place:


Each of those white squares has three über-bright white LEDs in the yellow stuff. I designed the circuit board to connect one LED from each of three SMD packages at a time, thinking I might use that layout to better dim the whole lamp head. Turns out, that circuit layout just makes for a really cool-looking circuit board.

Here is a photo of the underside of the LED lamp head with the resistors for each set of three LEDs in series:

Resistors on back side of LED head

There are three holes left, as of that photo, which will have the ground wire connected through and soldered. Each set of three LEDs and their resistor will have 12 volts supplied to them which will be controlled by a 3904 PNP transistor which itself will be controlled by the AVR microcontroller. The transistor will act as a switch for the pulse-width modulation provided by the microcontroller.

For those who aren't sure what pulse-width modulation is, the short story is that it is super-fast on and off switching. It's fast enough that you do not see a flicker. We use PWM to dim LEDs because they do not work efficiently without a specific voltage being given to them. So, we flicker the voltage that the LED likes really fast and emulate dimming. For each "flicker" of the switch, the amount of time that flicker lasts can be divided between on and off. The more on time we give the LED, the brighter it looks. The more off time, the dimmer it looks. Weird, yes. But, that's the right way to do it. PWM also works for DC motors and such. Discussion for another time. Maybe that's a discussion for someone who was properly trained in all this. I know enough to be dangerous, even though I try to be safe at all time.

LED Head on power cable

The cable carries six +12VDC wires and two ground wires to the back of the LED lamp head. The other end is currently plugged into the breadboard prototype of the controlling circuit. Here is the breadboard and labels for the various parts:

Breadboard of LED reading lamp

The power for the whole shindig is provided by a spare "wall wart" power supply, like the ones that power your TV boxes or network routers or wireless home telephone base stations. Here is the actual one I'm using, the end of which I snipped off to be able to plug its wires into my breadboard:

12V Power Adapter

These silly things provide pretty craptastic power, as far as DC circuits are concerned. They pretty much always supply a voltage other than what the label reads. This particular one measure out at 15 volts. Voltage to spare, baby! What's important is how much power (amps) we need to draw from the thing. Our circuit cannot pull more milliamps from the adapter than it is labeled to be able to supply. Luckily for this little project, we're only drawing at maximum about 91 milliamps. Not much at all, considering we're powering 18 super-bright LEDs and a little computer-on-a-chip. The Radio Shack adapter I'm using provides up to 500 mA of current. We're good.

The Atmel AVR microcontroller (the model is an ATmega328P, which is complete overkill for this, yes, but I didn't feel like reconfiguring my customized Arduino IDE to work with one of my little 8-pin ATtiny chips) basically sits and waits for the pushbutton to be pressed. When it senses a press, it delays for 25 milliseconds to keep the switch from bouncing on and off (a thing called, "switch bounce"), then gradually fades the LEDs up to the next brightness level. When it hits the last level, the next button press will shut off the LEDs.

Hope you found that one interesting!

Swanky Chinese Lamp

I Love Chinese Lamp. OK, I am not making one of these and I did not make this one, but I consider this to be super-swanky and a must-show-off piece in my collection of strange old things.

I inherited this from my grandmother who passed away around Christmas of 2009. It's plastic, but my grandparents purchased it for-real in Hong Kong when they lived over there. It's dirt-old and reminds me of the leg lamp from the movie A Christmas Story. When my parents brought it down to me and my wife saw it, all I could say was, "It's frah-jee-lay." It's awesome is what it is.

This will be the first thing filed under, "Swank-n-Funk."