Paul Hubbard pfhubbard@ucsd.edu
April 19 2010

This project is Arduino and Python/Twisted code to implement a simplest-
possible 'office weather station' that presents temperature and relative
humidity readings via a webserver interface.

The sensors are:
 * LM35CAZ Nice, TO-92 cased, temperature sensor with 0-5VDC output and no
   external components required. A few bucks from National.
   http://www.national.com/mpf/LM/LM35.html#Overview
 * Ohmic Instruments SC-600 humidity sensor and signal conditioning module.
   http://www.ohmicinstruments.com/pdf/SC-600.pdf
   About $15, quite cheap for a sensor this nice. You need an external RC
   lowpass, so two more components in the circuit. See the PDF.

Here's a picture:
 http://github.com/phubbard/office-weather/raw/master/sensors.jpg

Software:
 * The Arduino sketch simply sends the two ADC counts, as integers, on
   a single text line once per second, nothing else.
 * The Python code, implemented as a Twisted app, uses their LineReceiver
   class to get notifications of each new line, after which it does the 
   parsing, linearization and units. Overkill but simple.

   The twisted code also adds a simplest-possible HTTP interface, running on
   port 2000. The format used is designed for ingestion into Cacti, for nice
   time-based RRD graphs.

Notes:
 * The Mac Mini I'm using to host this has to have the Arduino drivers in
   place to use the virtual serial port for communications.
 * I'm debating an ethernet shield, but $50 seems overpriced for now.