I wonder how to log temperatures in my home using a computer? I would like to read temperatures in several rooms and collect data to a simple PC, 24-hours a day.
Having the log-file with all values can then be used i Excel or some other prgm to make charts.
Simplicity and low cost are prefered!
Thanks!
/johbys

 

Well, the easy answer: it depends...

First of all, you need to tell what accuracy you would like.

The somewhat longer version:
1. You do of course need a sensor in each room
2. You need to get the signal into the PC

Most temperature senosrns produce analog signals in some way or another:
- Pt-100 and termistors vary their resistance according to temperature
- Termocouples give a small millivolt signal depending on temperture

So you need to convert whatever type the raw signal have to something you can find an A/D converter accept, the standard way is to put in a transmitter converting it to 4-20mA drop that over a resistor of 250ohm and you get a 1-5V signal (alternate: 500ohm and you get 2-10V). Connect this to a analog input card accepting the signal you are producing, find (or write) a driver and you're there (well you have to do the logging too of course).

thermistors are quite cheap, but most often not very linear or high tolerance, so you have to take care about that (not much hard, but anyway) You can - of course - skip the not so cheap standard transmitter and make one yourself - especially if you use the termistor approach.

Pt-100 are more expensive, but more linear and it is probably easier to find a suitable standard transmitter.

The pricing of termocouples is an area I don't know but surely someone else can say...

A good A/D board with some inputs costs some if you want to buy it, at least if you don't have any ISA slot in your computer, I am not faily up to date though so there might be some new board I don't know about.

An interesting solution is to use the game port found on most PC:s with a sound card, it accepts four analog inputs in the form of varying resistances. Pt-100 are out of the question here (too low resistance and too little variation) but it might be possible to find a suitable thermistor.

Another interesting solution is to use a IC called SMT160-30 from Smartec. They are (for instance) sold here:
http://www.elfa.se art. no 73-088-85. They provide the temperature as a PWM signal, linear. You can then use a digital input, for instance an input pin in the parallel port, a COM port or the game port. By measuring the on time compared to the entire cycle you get the temperature.
It is even possible to read this in a slow scan mode, where you read the port sigificantly slower than the PWM frequency and make a long term average. (This might rise protests from some readers, but it does work - the clocks are not syncronized - if you didn't understand the impact of that - don't complain!)

Hmm, might do that myself... putting a couple of them outside too...

/Johan Bengtsson

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One low cost and fun method is to use a basic stamp. You can get info at http://www.parallax.com/ or do a google search on "basic stamp and temperature". Also there are people that sell kits using the stamps and all you need to do is take it and plug it into your serial port.

 

Check out the ibutton and one-wire stuff from http://www.dalsemi.com
The DS1820 and the DS9097U are all you need to get started.

 

I have done this using 10kohm thermistors connected to the game port. A dual game port gives you four channels and the thermistors are extremely sensitive. Cost is the price of the thermistors as your PC already comes with a game port. You will need some code to read the game port and massage the values, but this shouldn't be hard to find/write. I did it in Turbo Pascal many years ago for a HVAC room balancing soft chart recorder. I have toyed with the idea of updating it for MAT. Accurate, sensitive, four channel temperature measurement for $10 and some time is still a good idea. It's pretty trivial if all you want is a log. The graphical chart recorder was >99% of the code.

Regards

cww

 

For very inexpensive hardware try:
http://www.hobbytron.net/product1430.html
a four channel temperaturemeter (serial port) for $27 USD. It also comes with its own software.

For additional (free) logging/visualation side check out RRDTool http://www.rrdtool.com/index.html

It can log periodic data and do time-scale agrigation to other logs for trending. It can also generate GIF or PNG images of the trends either statically or dynamically from a web page.

Examples of weather data collection from a Radio Shack weather station here:
http://www.quiknet.com/~twitham/wx200/Day.html
and other weather data graphing:
http://www.rrdtool.com/gallery/chris-01.html
http://bruno.chaumontet.net/baro/index.html

-Rob.

 

I have one of these, it works well, but is limited in the number of channels.
http://www.drdaq.com

Francis

 

There´s a very simple sensor check this link:
http://www.national.com/pf/LM/LM34.html

After that all you need is an AD converter and that´s it. Email me if you have more questions.

[email protected].

 

Jonh,

There are some companies in the market that offer web solutions that work even in a HandHels (Compaq IPaq for instance). If you enter in www.indusoft.com you will see a very good solution for your problem.

 

You can found an electronic that read wireless termos from Oregon Scientific and wireless sensors from Visonic, have a RS232 connection, in http://www.domodesk.com search for DD-4471..take a look a ref. DD-5230 SMS control with thermal sensor include

Cheers!

 

A very simple and inexpensive way is by using one of the Smartec interface boards for use with the Smartec digital sensors. The interface boards are available for 4 or 8 sensors and allow cable lengths of 20 mtr. Have a look at http://www.mmselectronics.co.uk/indexsmart.htm
for more information, part numbers SMTAS04 or SMTAS08. The parts are available from MMS-e.