Too hot or too cold? Make it just right (and make Goldilocks proud) by building this dual-purpose device.

Down here in Arizona, we've got some pretty hot summers, at around 120 degrees. And inside, it gets up to about 88, which is a bit hot for my taste, especially when I've got my computer on- then it's even worse.
Or, if you live somewhere cold and wish your room was warmer at night, just flip a switch and your wish will be granted with this air cooling and heating machine.

And it's cool looking too!

Step 1: Materials

Oh man. This project requires a bunch of stuff, but you probably have most of them lying around from old broken things.
You do keep old things you don't use any more in a parts closet, right? Good.

-2 80mm computer case fans: I used one of a normal thickness and one half-sized one with more blades. You'll see why later.
-A transformer: I got mine from an old speaker set that I converted to run on batteries. It steps 120VAC down to 13.5VAC.
-4 diodes for making a bridge rectifier: Also from the speaker set; converts AC to DC.
-A 4700 uf capacitor: That's all I know about it. It just came from the speaker set, but I only know that it's 4700 ohms. It filters the DC current so it doesn't pulse.
-A 60mm x 60mm heatsink: Mine's aluminum. Bought on eBay. Right after I got rid of a bad computer motherboard I could have taken it off of. Oh well.
-Thermal Tape/Compound: Used for attaching the heating device to the heatsink.
-52mm Peltier Cooler/Thermo-electric cooler: Bought on eBay, it's the heart of this project. It gets hot on one side and cold on the other. You could probably find one on an old camping cooler along with the heatsink.
-A 6"x4"x2" project box: A bit tight for this project, you could get one that's a little larger.
-3 SPDT toggle switches, or 2 SPST and 1 SPDT toggle switches: For switching things on and off.
-A general purpose PC board: Got it at RadioShack; it came with two boards with 213 holes each. Perfect for this.
-2 1.5K ohm resistors: For the LED's.
-2 LED's: Any color, I choose one green and one red.
-A piece of flexible plastic: I got mine from the bottom of a dead power supply, but you could use anything that's thin and non-conductive.

And some basic tools:
-Soldering Iron
-Rosin Core Solder
-Drill with bits
-Hole-Cutting Bit
-Dremel with Cut-off Discs (Best tool ever!)
-Insulated Wiring
-2-prong electrical plug with cord
-Heatshrink Tubing or Electrical Tape
-Hot Glue Gun: (Optional)

Step 2: Wiring the Circuit

For your benefit (and mine for not having to explain everything) I've included a schematic/wiring diagram of the circuit. I will, however explain the flow of electricity to you can get a better understanding.

The electricity flows from an electrical outlet into the two leads of the transformer (polarity does not matter, just make sure you know which side of the transformer is the input and which is the output). Then, converted from 120VAC to 13.5VAC, it flows through a bridge rectifier circuit with the capacitor (see the second image, courtesy of Wikipedia). The bridge rectifier changes the AC voltage into a pulsating DC voltage with a + and - , and the capacitor (wired as shown, make sure you wire the + to + and the - to -!!!!!) filters the current to smooth out the pulses into a constant flow of electricity. From here, the negative lead goes to the first switch's middle prong. One of the other prongs is then connected to the middle prong of the other two switches, as well as to an LED with a resistor (resistance will vary depending on your transformer). This LED is then connected directly to the + lead of the capacitor, making a circuit.
Moving on to the second switch. Wire one of the outer prongs of the switch to the - lead of the Peltier unit and wire the + lead directly to the + lead of the capacitor. Wire this same prong to another LED and resistor (make sure you've got the correct polarity on the LED: the notched or flat side is usually negative). Then wire the + lead of the LED to, you guessed it, the + lead of the capacitor. The center prong of this switch should be connected to the first switch.
Finally, the last switch. The middle prong is connected to the other two switches. Connect the - lead of one fan to an outer prong and the - lead of the other fan to the remaining prong. Then connect both of the + fan leads to the + lead of the capacitor.

Make sure everything's insulated with tape or heat-shrink tubing as well.

You're done wiring!

Step 3: Drilling & Cutting

Boys and girls, it's time to break out your drills and Dremels!

If your transformer is a wee bit too tall to fit in the project box, you're going to have to do what I did- Dremel a nice hole for it to stick out of. Look at the 2nd picture to see how it will fit. Try to put the transformer as close to the end of the box as possible.
I don't have a picture, but if you look at the 2nd picture, you can see how I cut a (really crappy) hole in the box for the fan. Just use the biggest hole saw you have and then slowly make it bigger by using smaller hole saw bits until it gets to be the size of the fan. Also, drill a couple smaller holes for screws to hold the fan in.
Cut a small hole in the back (opposite the transformer) of the box for the two leads of the thinner fan, then run them through and solder. Make sure you cut the hole BEFORE soldering, otherwise you'll just have to unsolder the connections to run it through. You could also cut a small slit in the box where the lid connects to just set the wires in, but it won't look as pretty.
Next, cut a rectangular hole JUST the size of the Peltier cooler in the top of the box (not the lid!). You might have to cut a couple slits for the leads to rest in as well. Make sure that the side that gets hot is facing away from the box and the cold side is facing in.
While you're looking at the top of the box, cut three holes for the toggle switches (mine were 1/4") and try to make them in a straight line, equidistant from each other. Drill a couple of smaller holes for the LED's as well. I put these holes next to the 1st and 2nd switch.
Drill a few holes in the transformer side of the box for some air flow past the components. That transformer and those diodes get hot, you know!
Finally, drill a few large holes on the side of the box with the Peltier unit. These holes will be the ones that cool air is blown out of.
Put away your tools, cause you're done with cutting!

Step 4: Various Things...

Some various things to do to complete the project.

First, attach the thicker fan. You want to place it so that it's blowing INTO the case (there should be some arrows in the plastic near where the wires connect to show you how the air flows. You might have to cut off all the other plastic tabs on the fan to make it fit against the side of the box and mesh with the component board. Using a couple small screws that fit in the holes in the fan (and in the holes you cut in the box), attach the fan and a fan grill. You'll probably only be able to attach 2 screws. Then, using some needle-nosed pliers, bend the two remaining "arms" on the fan grill 90 degrees to make little feet. These will hold the fan up off the surface its on so it will be able to get decent air flow.

Next!

Using some thermal tape or thermal compound, attach the heatsink to the top of the Peltier unit. The heatsink basically just rests on top of the case. I used thermal tape to hold things together, but if you use thermal compound, you'll probably have to engineer some sort of brace system to hold them together.

Cut a piece of thin plastic (3rd picture) to use (1) to prevent a short circuit between the transformer and a switch and (2) to prevent all your chilled air from blowing past the hot components and coming out hot. Some air will be blown past them to cool it a bit, but not as much as there would have if the plastic was not in place. You'll need to tinker around with cutting sections out of the plastic for the wires to go through.
Just sort of place the PC board as close to the side of the case as possible so that the fan will fit. Make sure there aren't any short circuits! You can add a bit of hot glue to keep it on the side, but I find that the fan pushing against it works well enough. Plus, I was out of hot glue.

And....
Finally, grab your AC plug with a cable, strip the wires inside as well as the wires to the transformer, insulate everything, and solder the one wire form the transformer to one wire of the plug. Do the same with the other wires.

Step 5: Close It Up!

After some careful maneuvering of the transformer, fan, wires, and circuit board, run the AC cable through the transformer hole and close up the lid. Just thumb tighten the screws to hold it on for now.
Plug it in, and flip the first switch. One of the LED's should light up, and a fan should start spinning. When you flip the third switch, the other fan should start spinning instead. Now flip the second switch. The other LED should light, and the first LED will probably dim. The fan will slow down as well. This lets you know that the Peltier unit is working. Place your hand on the heatsink. Within a minute, you should start to feel it get warm. If the bottom fan is running, you should feel cooler air blowing out the back of the case. Thus, the cooler.
If you place the smaller fan on top of the heatsink so that it's blowing down, and you align the front edge of the fan with the front of the heatsink, hot air will be blown into the room when that fan is on. Thus, the heater.
Oh, the reason I used the smaller fan with more blades here is because I discovered that you get more airflow than using the thicker fan.

I'm sure there are ways that this project could be enhanced or made to work better, so if you have suggestions, please comment! Thanks, and enjoy this useful project!