Friday, April 27, 2012

Thermoelectric (Peltier) Wine Cooler

Have you ever bought a wine cooler?  They are huge, bulky and ri-donck-u-louse looking.  First off, it does not make any sense to design a wine cooler as a cube.  The main goal should be to minimize the surface area of the enclosure as that is where heat transfer occurs and thus is a large dictator of how much energy you must feed the system.  Wine bottles naturally stack in a triangle and in this fashion they are packed the tightest.  So, why not design a triangle shaped enclosure that minimizes how much heat we must pump out of the enclosure and thus how much energy we are using?  Seems reasonable, right? Here is a first pass at doing so.

First off, some initial calculations to get a feel for how much heat we gotta pump outta this thing.  We will shoot for a cooler roughly sized to hold three wine bottles or a sixer of Busch Light, yum.  We will only consider conductive heat transfer for the time being.  The amount of energy we need to pump out of the cooler through the TEC (Qpump) is then equal to the amount of heat weaseling its way through our insulation (Qin) and the amount of power we are feeding to the TEC (Qjoule).  Qjoule will not actually be the amount of power we are feeding the TEC but we can use it as a worst case scenario.

Image 1:  Initial thoughts on size and heat transfer involved

 Based on some proposed dimensions for the cooler, an estimate of the k value of our insulation (the k value just quantifies how good or bad insulation is), and the desired temperature of our wine (55*F) relative to normal room temp (75*F) we can calculate Qin.  I doubled the Qin value as originally calculated it was the absolute minimum amount of heat needed to be pumped to retain desired temperature if all else were to remain constant.  As there will also be some small amount of conductive and radiative heat transfer taking place we will need a little more heat pumping capacity.  We also might run into different environments where it is necessary to pump more heat, aka: if room temp is greater than 75*F.

 Image 2:  Solving for conductive heat transfer and power added by TEC

 Here is an ugly looking diagram of how the components will all be connected.  I will post later exactly what was used to create the cooler once I fine tune it along with a cleaner diagram.

 Image 3: Component diagram

Note: a wine bottle at room temperature that is put in a wine cooler holds latent heat that also needs to be pumped out of the enclosure.  This was not included in the initial sizing of the TEC due to the fact that if you can pump more heat out than is entering from the outside surroundings (Qin) this latent heat will eventually be pumped out as well... it just might take awhile.

So as it stands, with some Busch League All-Star (definition: bad, crappy, swagged, horribly awesome) code I slapped together here is what it looks like and how it is functioning.

Something has gone horribly wrong with uploading this video so here is the link to how the user interface is currently functioning (can't embed vimeo :(  ): 

 Image 4:  Outside of enclosure, wiring yet to be subdued

Image 5: Looking in the side hatch, foam insulation visible

More to come on this project...

Tuesday, April 17, 2012

Dirt Cheap Microcontroller Project

Here is a great introductory project to microcontrollers and more specifically the MSP430 by Texas Instruments.  This is a fantastic way to get your feet wet in the world of microcontrollers.  Its very cheap and can be reproduced for only around $25.  The battery pack shown in Image 1 is unnecessary as you could power the LCD from the MSP430 development board.

Image 1: An MSP430 displays characters on an LCD screen

Here is all you will need to reproduce what you see above:


LCD - $9.95

MSP430 Launchpad (Microcontroller and development board)- $4.30
(Note: you will also need an IDE, Integrated Development Environment, to write code that will control your microcontroller.  This can be found on the TI website above as well.  There are two different ones you can download, either Code Composer Studio or IAR Embedded Workbench)

Breadboard Wiring Bundle - $6.00

Breadboard - $5.00

Helpful Tutorial Resource

This blog will walk you through everything you need to know about the MSP430, the IDE, and running an LCD screen.  It even has code examples you can grab.  There is plenty of other useful information here as well.  The tutorial specifically on LCDs is #14a and can be found in the September of 2011 archive.

OpenIdeo: Web Entrepreneurship

OpenIdeo is hosting a challenge to help spur web entrepreneurship.  Take a peak at our concept and add one of your own!

Friday, April 6, 2012

BrainBlox: Get your H-Bridge on

Want to enforce total control over that DC motor that has been bad mouthing you for the past week?  Build yourself an H-Bridge (motor controller) and dominate.  With a little time and not too much money you can do just that.  Here is a great tutorial:

Here is an H-Bridge one of us made.  An Arduino is controlling a small DC motor through an H-bridge.  The analog signal (pulse width modulation) being sent to the motor is also output on the LCD screen and is controlled via a potentiometer (variable resistor).  When the potentiometer is rotated the analog signal changes between 0 - 255, is output on the screen and dictates how fast the motor spins.