Its a simple project minimal skills needed.
Drawings are made using: Fritzing
Code Written using Codebender
The cold plate got to -20c
Watter in the cup measured @ 5.5c compared to icecube @2.5c
Step 1: Things To Find
220ohm resistor (i have used 3 x750 in parallel as couldn't find anything smaller) anything from 100 to 220 will do.
12v dc fan 3 wire but 2wire will do the same job.
TEC1-12704 TEC Thermoelectric Cooler
12volt DC adaptor 2.5 amp
LM355Z Temperature Sensor
Step 2: Wiring everything
Pin1 - Digital I/O 9 via 220Ohm resistor
Pin2 - Ground
Pin4 - DC fan Positive
Pin5 - 12V positive
Ground - to 12v Ground
LM335 Temp sensor
Vin - 5V arudino
Grn - Ground arduino
Vout - Analog 0
Positive to 12v DC positive
Negative to 12v DC negative
Better would to add a switch or another Optocoupler to turn ON/OFF
Step 3: Building
The hot side is facing down another layer of thermal paste and a massive heat-sink to absorb all the heat (you don't want it to effect cooling).
Glue gun to glue Thermoelectric Cooler to the heat-sinks.
And a fan attached to the heat-sink which is activated when temp reaches 34 degrees Celsius, then runs for 20 seconds and start monitoring temperature again.
If heat-sink gets too hot it will kill the cooling power...
The code is http://codebender.cc/sketch:8769
I have used LM335 Library which help with measuring temp: you can find it @ https://code.google.com/p/alm335/downloads/list
If you dont know how to install it here is great tutorial @ http://learn.adafruit.com/arduino-tips-tricks-and-techniques/arduino-libraries