pool temperature monitoring

I have been wanting to build an arduino based project for a while now, and it looks like I finally found my first project. I need to monitor the temperature of my above ground pool, before and after the solar heater.

I was thinking about using the Goldline 10K thermistor sensors, since they seem to be made for this application and are relatively easy to mount. However, they also seem to be the hardest to interface, since they aren't linear.

I can't find much info about people using an Arduino based controller interfacing these type of sensors (remember, I am new to all of this), but also don't want to buy an expensive Datanab (plus I really want to get experience working with the arduino platform).

What hardware (i.e., which kit and add-ons) would you guys recommend to interface these probes? I basically want to monitor these temps, and spit them out via a serial port every minute or so.

I'd appreciate any input you might have ;)

Rather than use thermistors which are a right royal pain in the backside to get sensible readings out of, I'd go for Maxim/Dallas DS1820/ DS18S20/DS18B20 digital thermometers and encapsulate them myself with potting compound in a suitable piece of tube. They are pretty easy to do in the TO-92 package and are very easy to hide.

You could go halfway Datanab and buy these http://datanab.com/sensors/1Wire_Potted.htm . They are DS18B20s ready encapsulated which will interface to an Arduinio without too much difficulty.

I was actually considering 1-wire devices, my main issue is how to install these (and are they rated to be in chlorinated water 24/7)? With the goldline sensor, you drill a hole in the PVC piping, and insert them. They have a gasket, and you 'clamp' it in place.

I found stainless steel versions of that 1-wire sensor on ebay, so I would definitely prefer to go the 1-wire route assuming it will last.

I've used a thermistor with no problems. I could share some code that I found in someone else's post if you want. I have a 1-wire sensor that I haven't tried to interface yet. Those look like a pretty good option also.

which arduino kit did you use? I am still trying to figure out what kit is the right choice, and what addons I need.

The code for thermistors usually only works with the same spec of thermistor, if your particular thermistor isn't the same spec the figures are miles out. I couldn't find any code that gave believable readings with the ones I have. I worked for a time with a homebrew lookup table before I gave up and bought the DS18S20s I use now. I would think ones encapsulated in stainless steel should be next door to bomb proof. I have a home monitoring system which also controls the heating. Its based on a Duemilanove :

http://pluggy.is-a-geek.com/index.html

my main issue is how to install these

I used to service the electronics for a locally manufactured spa pool. They used to fit the sensor (LM35 with some heatsink compound) inside a stainless sleeve, about 8mm diameter. This screwed into a socket, and had a compression gland to seal it.

It was standard electrical fitting, that they swopped the cable for the sleeve. It worked very well as the whole assembly flattened out any sudden temp spikes, and luckily for me made them removable.

I would use the dallas chip, as the other options need calibrating, etc, etc.

Cheers Mark

How to install...

Are ALL the pipes plastic? No metal anywhere (for good head conduction)?

I'm the nervous type.... I'd hate to damage the plumbing of the pool's systems. Maybe a job for a professional, after he is made aware of what you need? The 1-Wire temperature sensors look like little three legged transistors... and lots of other sensors would be similar.

If there is no metal in the plumbing, it may be to avoid corrosion issues....

I don't think it would be good to use a solution that leaves the chance of the sensors becoming wet. Keep a metal, or even plastic, "wall" between sensor and water, even if it does introduce some lag in readings.

Good luck... Tell us how you solve this one.

You need something like this http://www.sensorsone.co.uk/products/446/157/TS100-Compact-Temperature-Transmitter-and-PT100-Probe.html

Depending on what you buy it can output 0-5v 0-10v 4-20ma 0-20ma etc

It's RTD based with a converter inside to generate the signal. It's highly accurate. It's expensive. You will need instructions on how to mount it properly.

Designing devices for a pressurized environment can be difficult. You might see about adding a short length of corrosion resistant stainless pipe and trying something like this. Or making it. http://www.reuk.co.uk/Pipe-Clip-Temperature-Sensors.htm

BTW the pipe clip may be desirable for a solar heater according to the makers information. The non-linearity of the device would require a lookup table or formula be solved in the Arduino or in the device reading data from the Adruino. It would also require calibration to know what to feed into the lookup table or formula which means providing a range of known temperatures and recording the output of the device. Somewhat tedious for the hobbyist as the only calibration standards most have are icewater and boiling water.

Have fun, be safe.