I have several Christmas village buildings and props that I put up each year on my fireplace mantel around Christmas. This year I decided to make streets and a backdrop for it. The streets and backdrop are ink-jet printed on thick photo paper. The backdrop was also glued to foam-core board.
Over the years I’ve accumulated quite a large collection of textures for use in 3D modelling on the computer. So I had some nice cobblestone, flagstone, grass, and snow textures on hand, as well as photographs of street details like victorian-era manhole covers and street drains. I used the flagstones plus drop-shadows to depict the curbs. I masked the snow layer with a grunge texture to allow some of the grass to show through and used a textured eraser to remove snow from key areas of the street. The picture to the right shows one of the streets I made.
Department 56 made the buildings and other assorted props for my village, so to make the backdrop, I used pictures of some of their other buildings pasted in various orientations in layers. Lower layers for buildings that were farther away. For each lower layer, I shrunk the buildings a little bit more. Between each layer is a faint blue fog. At the very back is a texture that fades from night blue at the horizon to black at the top. Some falling snow completed the picture. The picture below and to the left is part of the resulting backdrop.
The next item that needed work was the streetlights. They were intended to be powered by a pair of C-cell batteries, but as I found out last year, two C batteries could only run the streetlights for about half an hour. Department 56 sells a power adaptor for these that can plugged in to an electrical outlet, but I figured I had enough parts on hand to make my own. And thus began one of the most hacked up circuits I’ve ever made.
The two C batteries were connected in series and there was nothing else in that part of the circuit, so they provided 3 volts to the lights. The lowest voltage wall adaptor I had to spare produced 10 volts, so I would have to reduce the voltage a bit. I had some 3.3v linear voltage regulators on hand, so I threw together a circuit with one of those plus the required capacitors. I also threw a diode into the input to protect the voltage regulator in case I hooked up the power backwards. I tested the output and it was indeed 3.3 volts, and hooked it up to the lights, which lit up beautifully … and then ten minutes later I burnt one finger on the voltage regulator and another on the diode. This was running much hotter than I had expected!
The fact that the batteries could only run the lights for about 30 minutes should have been a clue – these lights draw a lot of current! (well lots for my little bits of electronics) It turns out that they drew 0.6 amps at 3.3 volts. This was within spec for all the parts I used, but it was obvious that I was going to have to put a heatsink on the voltage regulator and do something about the diode as well. Linear voltage regulators are not very efficient; they reduce the voltage by wasting the energy as heat. Since I was going from 10 volts to 3.3 volts, this meant that 6.7v * 0.6A ≈ 4 watts was being turned into heat in the voltage regulator. The first heatsink I tried wasn’t large enough (actually, I did some calculations later and they showed that it would keep the voltage regulator below its max allowable temperature, but it still meant the whole thing was hot enough to burn flesh, which bothered me), so I jammed that first heatsink into a larger one. That worked quite well. All that current was also flowing through the diode I mentioned earlier and that was also getting quite hot. Since the diode was just there in case I made a mistake and hooked the power up backwards, I decided to just take it out of the circuit – I soldered a wire to bypass the diode. So now I had an ugly little circuit board with wires everywhere and a diode that wasn’t actually even being used. But it worked!
Later I found a 5v wall adaptor, so I put that to use instead of the 10v one. This meant the voltage regulator didn’t have to reduce the voltage nearly as much, which helped with the heat problem.