Pond Temperature - how it works

Parts: 

• 4@ 1-wire temperature sensors -  DS18S20
• 1@ 1-wire temperature to serial microprocessor module http://www.phanderson.com/tm125.html

The Sensors:

The temperature sensors are from Dallas Semiconductor - part # DS18S20 - these devices, and others in Dallas Semi's 1-wire stable, communicate over a single piece of twisted pair wire (1 wire for data and 1 wire for ground) - each has a unique serial number and can be polled to report their readings.  The DS18S20 is accurate to .5 degrees C.  See http://pdfserv.maxim-ic.com/en/ds/DS18S20.pdf for details

The devices are located in the main pond at 32" (the deepest point in the pond), 12" and at 6" in the filtering bog.  There is also a 4th sensor about 24" above the pond.   It is exposed to the sun so that the length of sunlight on the water can be determined by the extreme temperature swings reported when the sun is falling on the sensor.  All sensors are housed inside of standard 1/2" PCV pipe - a small hole in end caps, sealed with silicon glue, exposes the ends of the sensors to the air or water.

The sensors are wired in parallel and connected to one pair of a 100' Cat 6 twisted pair cable that runs from the pond to the basement workshop.  The device that reads the sensors is from:  http://www.phanderson.com/tm125.html, a really great source of such microprocessors, sensors and code to use them.  The device connects to the twisted pair from the pond sensors and to a PC via a standard serial cable.  A simple Quick Basic program sends a single character to the serial port on the TM125 device to initiate a read.  The program reads the four sensors and stores the results to a file.  Another QB45 program reads the file, collects the most recent 150 sets of readings and creates a HTML document that is FTPed to the web server.  All of this happens every 15 minutes and is controlled by a batch file called by Windows Scheduler.

First program:  1-WIREA.BAS

• calls for readings and writes to file
• note that new readings are appended to the file and it can grow quite large!
• a good bit of the code deals with error corrections and retries should readings not be accurate

Second program: 1WIRHTM2.BAS

• reads the text output file from 1-WIREA.BAS
• creates a table containing the last 150 readings in HTML

Sample data file  1WIREOUT.TXT

• four readings per time period (one for each sensor)
• fields are date, time, sensor number, last 2 hex digits of sensor ID, Celsius temperature, Fahrenheit temperature

Graphing - NEW

The original program placed the temperature data onto the web in table format.  I had been interested in showing it in a graph as well but did not have an appropriate tool until I ran across a program called GUNPLOT.  Gnuplot is a command line driven graphing program that can read tabular data and create a graph in GIF, PNG and other image formats.

In order to incorporate Gnuplot into the temperature program all that was necessary was to create a text file that contained the data to be graphed, define the graph to be created by creating a script file and to execute a command that told Gnuplot to read the file based on the command script sending output to a GIF file.

Here are the files along with some comments:

GRAPOUT.TXT - the file created by the 1wirhtm2.bas program..  Each line in the file contains the date and time of the temperature reading, the ambient temperature, Main 32, Main 12 and bog temperatures in Fahrenheit

LAST150.PLT - a script file that defines the graph (see notes below)

LAST150. GIF - output from Gnuplot.

SINCEOCT.PLT and ALL.GIF - script and output for all readings since starting in October, 2003

Notes: 

• the first three lines set up for gif file output, name it and set it's size (long and narrow)
• the next three lines set the tics, grid and title
• the next two set x and y label titles
• "set key below" puts the line labels under the graph
• Plot is repeated 4 times (separated by commas) to get 4 lines on one graph
• "set output" is there to close the GIF file - if you forget it the file will not be readable (0 bytes)