I loaded up Apple’s home page today to see the App Store downloads counter looking like this:

After taking a close look at how it works, the counter uses javascript to continue the count from this text file:
http://www.apple.com/autopush/us/itunes/includes/countdown.txt
My system time was off due to setting the time zone incorrectly.

Max

After seeing an Instructable on Digg for making a USB powered fridge, I decided to incorporate the concept into a backpack. For those who don’t know, the USB fridge uses a Peltier Unit to cool the contents. When power is applied, a Peltier Unit makes one side extremely cool and the other side extremely hot. If the power is reversed, the cool side becomes the hot side and visa versa. The only problem with this is the fact that while cooling the users back, the hot side would be accumulating mass amounts of heat inside of the backpack. My solution to this was to use a processor heat sink along with a fan to push this heat out of the backpack. The cool side of the peltier unit is placed on a piece of sheet metal that will be exposed to the users back for cooling and/or heating. Thanks to my friend Miles for helping with the fabrication process! Go check out his site called Motor Mayhem. Here is how I made the backpack:

Materials:
1 x Jansport backpack
2 x 91.2W Peltier Units - ( 12v * 7.6a = 91.2W )
2 x Processor Heat Sinks w/ Fan
1 x Tube of Thermal Gel
1-2 x 12V 5lbs Motorcycle battery
2 x Different Size Tupperware Containers
1 x 8.5×11 Piece of Sheet Metal
1 x Switch
Some Spare Wire

Procedure:
Step 1: Cut the piece of sheet metal to the preferred size. Make sure it fits on the back of the backpack!

Step 2: Make some holes around the perimeter of the piece of sheet metal. These will be used later to attach the metal to the backpack.

Step 3: Measure where the peltier units will be placed. Make sure when the heat sinks are spaced apart so the heat sinks will fit! Then drill the holes required to attach your heat sink above the peltier units.

Step 4: Apply some thermal gel to each heat sink. Add a peltier unit to each heat sink and put thermal gel on top of each peltier unit. Then apply thermal gel to the spaces on the sheet metal where each peltier, heat sink pair will be placed.

Step 5: Using the screws included with each heat sink, attach them to the sheet metal through the holes drilled earlier.

Step 6: Now that the cooling unit has been made, an air venting system needs to be made. To do this, get a tupperware that seals everything between the fan and the sheet metal and cut a hole in the bottom that matches the fans. Then get another tupperware on top that will act to cover the fans from the back of the backpack and guide in air from the sides. The fans will be blowing air onto the heat sinks, so air will come in the sides of the top tupperware and get blown on the heat sinks and then released out into the open.

Step 7: Try connecting the fan wires in different combinations until the positive and negative leads are found. Make sure when connected the fans blow air on the heat sinks. Then solder the wires of each fan to those of the peltier units in parallel. Now connect each peltier, heat sink pair together in series.

Step 8: Cut a hole in the backpack that’s just a little smaller than the piece of sheet metal. Cover the seams with duct tape so they don’t fray. Now use some thick thread or thin wire to sew the sheet metal to the back of the backpack.

Step 9: Now use some thick thread or thin wire to sew the sheet metal to the back of the backpack

Step 10: Now cut a hole on each side of the backpack for air intake. Then cut one more at the top to let the warmer air out. I cut mine around the neck because by the time it reaches the top of my backpack it was slightly cool.

Step 11: Solder one lead of some wire to a wire going to the cooling unit. The two leads left will connected to the battery while the two leads on the other end of the wire will be for the switch.

Step 12: Zip up the backpack and turn it on!

Modifications:
I recommend putting a mesh screen over the vents to keep big particles out of the fans. If you want to make this into a heating backpack reverse the leads on the peltier units so the hot side is on the sheet metal and the cool side is on the heat sinks.

I hope you all enjoy it :)

Max

I removed the old stuff here and put up a nice shiny new blog :)

Max