Build Instructions

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• 1

  Raspberry Pi B+ Setup

  Install Raspberry Pi OS as usual.  The TEMPer USB thermometer needs a Python utility called "temper-poll":

  https://github.com/padelt/temper-python

• 2

  Temperature Logging

  Create a script that calls temper-poll and a task in /etc/crontab to record the temperature every five minutes.  The code for this project expects a log file in the following format per line: 

  <UNIX timestamp> <temperature (F)> <MM/DD/YY> <HH:MM:SS>

  You will need to run this cron job for several months in order to gather enough useful data.

  Example logging script (PHP):

  <?php
  
  $adj = 0; // Temperature adjustment in Fahrenheit.  Calibrate with another trusted thermometer after recording some samples.
  
  $d = Array();
  exec("temper-poll",$d);
  if(isset($d[1])){
    $s = $d[1];
    $s = explode(' ',$s);
    $s = $s[3];
    $s = str_replace('°F','',$s);
    $s = (intval($s*100) / 100) + $adj;
    $ts = time();
    $ds = date("m/d/y H:i:s");
    file_put_contents('./temper.dat',$ts.' '.$s.' '.$ds."\n",FILE_APPEND);
  } else {
    echo 'Could not read temperature.';
    exit();
  }
  
  ?>

• 3

  Conversion of temperature logs to audio

  The PHP and Python files provide two separate ways to convert the temperature logs to an audio file.  The resulting audio file will be in a 16-bit / 8 kHz sample rate format.  Temperature fluctuations will become audible sound.  It is a good idea to run some simple post processing on the resulting audio, namely a high pass filter around 120 Hz to filter out the seasonal temperature swings, followed by volume normalization.  There may also be transients worth filtering out in order to get the remaining audio levels to a decent range.

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