Pieces used:

• Raspberry Pi.
• Dallas 18B20 temperature sensor.
• Prototyping board and random bits of wire.
• Remote Debian server with a LAMP style setup
  

  ---

  The basic process flow:

  A cron job on the PI collects the current temperature from the 18B20 chip attached to the GPIO. It then inserts the temperature into a remote MySQL database on the big server. A cron job on the big server creates a PNG from the data using rrdtool. There is a link in the web directory to the PNG, which you see above.

  ---

  Here is the table creation commands.

  
CREATE DATABASE temp_monitor;

  USE temp_monitor;

  CREATE TABLE `temp_data` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `unixtimestamp` int(11) NOT NULL,
  `temp_f` float NOT NULL,
  `temp_c` float NOT NULL,
  `sensor` varchar(25) NOT NULL,
  `adjusted` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
  );
  

  ---

  Here is the cron job on the rPI that reads the temp and sends it to the big server in the sky.

  #!/usr/bin/python

  import time;
import httplib

  # Exampe temperature file output:
  # —————————————–
  # 77 01 4b 46 7f ff 09 10 6f : crc=6f YES
  # 77 01 4b 46 7f ff 09 10 6f t=23437
  # Config options:
  # Temperature “file”
  pin=0
  device=”28-00000441aeff”
  tempfile = “/sys/bus/w1/devices/”+device+”/w1_slave”
  outputfile = “/tmp/newtemps”

  # Get the temperature
  tfile = open(tempfile)
  text = tfile.read()
  tfile.close()

  # Split the text with new lines (\n)
  # and select the second line.
  secondline = text.split(“\n”)[1]

  # Split the line into words, referring to the spaces,
  # and select the 10th word (counting from 0).
  temperaturedata = secondline.split(” “)[9]

  # The first two characters are “t=”, so get rid of those
  # and convert the temperature from a string to a number.
  temperature = float(temperaturedata[2:])

  # Put the decimal point in the right place and display it.
  temperature = temperature / 1000

  # Convert to fahrenheit
  ctemp = temperature;
  temperature = 32 + ( temperature * 9 ) / 5

  # Get time
  ut = time.time()
  localtime = time.localtime(time.time())

  #Output
  outline = ‘{} {} {} {} {} {} {}\n’ . format(localtime[0], localtime[1], localtime[2], localtime[3], localtime[4], localtime[5], temperature)

  ofile = open(outputfile, “a”)
  ofile.write( outline )
  ofile.close()

  # send the temp to the server
  conn = httplib.HTTPConnection( “database.myserver.org”)
  conn.request(“GET”, “/sensor_input.php?c=” + str(ctemp) + “&s=28-00000441c8b3&t=” + str(ut))
  r1 = conn.getresponse()
  

  ---

  Here is the PHP code that accepts the data from the PI and stuffs it into the DB.

  
// inputs:
// Required:
// c = temp in celcius
// s = id of sensor providing the data
//
// Optional:
// t = unix time stamp. If this does not exist use NOW()
//

  function error_out() {
  print “Something is missing.&th;br>&th;pre>\n”;
  print_r($_REQUEST);
  exit();

  }

  function clean($in) {
  return preg_replace(“/[^A-Za-z0-9\.]/”, ”, $in);
  }

  if( isset( $_REQUEST[‘c’] ) ) {
  $c = clean( $_REQUEST[‘c’] );
  $f = ( ( $c * 9 ) / 5 ) + 32;
  } else
  error_out();

  if( isset( $_REQUEST[‘s’] ) )
  $s = clean( $_REQUEST[‘s’] );
  else
  error_out();

  if( isset( $_REQUEST[‘t’] ) )
  $t = clean( $_REQUEST[‘t’] );
  else
  $t = ‘NOW()’;

  // For some reason we periodically get two known bogus numbers
  // 185’f and 32.1116’f. So we are going to toss them out
  // even if on the off chance they were valid.

  if( $f == 185 or $f == 32.1116 )
  exit;

  $query = “INSERT INTO temp_data ( unixtimestamp, temp_c, temp_f, sensor ) ” .
  ” VALUES ( $t, $c, $f, ‘$s’ )”;

  $link = mysql_connect(‘localhost’, ‘fakeUser’, ‘fakePassword’)
  or die(‘Could not connect: ‘ . mysql_error());

  mysql_select_db(‘temp_monitor’) or die(‘Could not select database’);

  // Performing SQL query

  $result = mysql_query($query) or die(‘Query failed: ‘ . mysql_error());
  

  ---

  And here are the cron jobs on the big server that creates the image.

  ---

  Runs every minute.
  
#!/bin/bash
  cd /var/www

  F_BASE=”sql//mysql/host=127.0.0.1/dbname=temp_monitor/username=fakeUser/password=fakePassword//temp_data/unixtimestamp/temp_f/sensor=’2800000441c8b3′”

  C_BASE=”sql//mysql/host=127.0.0.1/dbname=temp_monitor/username=fakeUser/password=fakePassword//temp_data/unixtimestamp/temp_f/sensor=’28dfca4140090′”

  rrdtool graph daily.png –imgformat=PNG –start=-1day –end=now –width=400 –height=200 \
  “DEF:temp_f=$F_BASE:min:AVERAGE” \
  “LINE1:temp_f#FF0000:Office” \
  “GPRINT:temp_f:MIN:Min\: %6.2lf” \
  “GPRINT:temp_f:AVERAGE:Avg\: %6.2lf” \
  “GPRINT:temp_f:MAX:Max\: %6.2lf” \
  “GPRINT:temp_f:LAST:Last\: %6.2lf” \
  “DEF:temp_c=$C_BASE:min:AVERAGE” \
  “LINE1:temp_c#00FF00:Remote” \
  “GPRINT:temp_c:MIN:Min\: %6.2lf” \
  “GPRINT:temp_c:AVERAGE:Avg\: %6.2lf” \
  “GPRINT:temp_c:MAX:Max\: %6.2lf” \
  “GPRINT:temp_c:LAST:Last\: %6.2lf”

  rrdtool graph weekly.png –imgformat=PNG –start=-1day –end=now –width=400 –height=200 \
  “DEF:temp_f=$F_BASE:min:AVERAGE” \
  “LINE1:temp_f#FF0000:Office” \
  “GPRINT:temp_f:MIN:Min\: %6.2lf” \
  “GPRINT:temp_f:AVERAGE:Avg\: %6.2lf” \
  “GPRINT:temp_f:MAX:Max\: %6.2lf” \
  “GPRINT:temp_f:LAST:Last\: %6.2lf” \
  “DEF:temp_c=$C_BASE:min:AVERAGE” \
  “LINE1:temp_c#00FF00:Remote” \
  “GPRINT:temp_c:MIN:Min\: %6.2lf” \
  “GPRINT:temp_c:AVERAGE:Avg\: %6.2lf” \
  “GPRINT:temp_c:MAX:Max\: %6.2lf” \
  “GPRINT:temp_c:LAST:Last\: %6.2lf”
  

  ---

  Runs every hour.
  
#!/bin/bash
  cd /var/www

  F_BASE=”sql//mysql/host=127.0.0.1/dbname=temp_monitor/username=fakeUser/password=fakePassword//temp_data/unixtimestamp/temp_f/sensor=’2800000441c8b3′”

  C_BASE=”sql//mysql/host=127.0.0.1/dbname=temp_monitor/username=fakeUser/password=fakePassword//temp_data/unixtimestamp/temp_f/sensor=’28dfca4140090′”

  rrdtool graph monthly.png –imgformat=PNG –start=-1day –end=now –width=400 –height=200 \
  “DEF:temp_f=$F_BASE:min:AVERAGE” \
  “LINE1:temp_f#FF0000:Office” \
  “GPRINT:temp_f:MIN:Min\: %6.2lf” \
  “GPRINT:temp_f:AVERAGE:Avg\: %6.2lf” \
  “GPRINT:temp_f:MAX:Max\: %6.2lf” \
  “GPRINT:temp_f:LAST:Last\: %6.2lf” \
  “DEF:temp_c=$C_BASE:min:AVERAGE” \
  “LINE1:temp_c#00FF00:Remote” \
  “GPRINT:temp_c:MIN:Min\: %6.2lf” \
  “GPRINT:temp_c:AVERAGE:Avg\: %6.2lf” \
  “GPRINT:temp_c:MAX:Max\: %6.2lf” \
  “GPRINT:temp_c:LAST:Last\: %6.2lf”
  

  ---

  Runs every day.
  
#!/bin/bash
  cd /var/www

  F_BASE=”sql//mysql/host=127.0.0.1/dbname=temp_monitor/username=fakeUser/password=fakePassword//temp_data/unixtimestamp/temp_f/sensor=’2800000441c8b3′”

  C_BASE=”sql//mysql/host=127.0.0.1/dbname=temp_monitor/username=fakeUser/password=fakePassword//temp_data/unixtimestamp/temp_f/sensor=’28dfca4140090′”

  rrdtool graph yearly.png –imgformat=PNG –start=-1day –end=now –width=400 –height=200 \
  “DEF:temp_f=$F_BASE:min:AVERAGE” \
  “LINE1:temp_f#FF0000:Office” \
  “GPRINT:temp_f:MIN:Min\: %6.2lf” \
  “GPRINT:temp_f:AVERAGE:Avg\: %6.2lf” \
  “GPRINT:temp_f:MAX:Max\: %6.2lf” \
  “GPRINT:temp_f:LAST:Last\: %6.2lf” \
  “DEF:temp_c=$C_BASE:min:AVERAGE” \
  “LINE1:temp_c#00FF00:Remote” \
  “GPRINT:temp_c:MIN:Min\: %6.2lf” \
  “GPRINT:temp_c:AVERAGE:Avg\: %6.2lf” \
  “GPRINT:temp_c:MAX:Max\: %6.2lf” \
  “GPRINT:temp_c:LAST:Last\: %6.2lf”
  

  ---