Instrumenting a 3D Printer for Heat Testing

My DLP printer experiment is as much of tinkerers panacea as it is anything.  And I am ok with that as I expected as much.  I have version 1.2 of the printer and version 1.3 has just been released.  The difference between the two is all a matter of cooling.  Which is to say that version 1.2 ran hot!  With that knowledge in hand I designed a new case for the printer with cutouts for some new fans. But will both fans be needed and if so what way should airflow run?  These are the questions that I would like to answer!

To be able to answer these questions I needed a quick and dirty way to measure temperatures within the printer.  It would also be helpful to know when the UV array is lit and how much light it is producing.  I decided to use one of my many Arduino' for this task connected to three thermistors and a photo resistor.  Initially I will use a bluetooth adapter to talk back to my PC.  I also want to source power from the printer so I need to convert 12v to 5v to operate the Arduino.

Here is a picture of what I built followed by a brief description of the various components.

1. Arduino Nano - Cheap as dirt on eBay but a capable little chip.
2. Expansion board for the Arduino Nano. Breaks out every pin on the board adjacent to power for whatever you want to connect.
3. Power converter to take the 12v from the printer supply down to 5v for these electronics.
4. Bluetooth adapter for transmission of data back to my desktop.
5. Thermistor (more below).
6. Photo resistor (more below).
7. Temporary 5v power supply.

The thermistors and photoresistor all operate in a similar manner.  Temperature or light change their resistance.  I create a voltage divider with the variable sensor as one of the two resistors.  By measuring the resultant voltage I calculate a heat reading for the thermistors.  The photo resistor reading is not translated but just used raw.  Here is the Arduino Sketch that runs on this device.

The output of the above sketch is a simple CSV stream of values that I capture on my Mac and then feed to a spreadsheet.  A sample of the CSV and a copy of the end chart are shown below.