Computer interface to temp probe and 110V contactor needed

I am looking for a way to control the temp in my water bath heat exchanger for a stepped temperature mash recirculated system. I am sure this has been done before, but I have no experience in how to get a computer program to control other circuits. Please enlighten me. Thanks!

Fermenter 1 - pale Lager
Fermenter 2 - Winter Warmer ale
Fermenter 3 - cocao-coffee ginger ale
Frementer 4 - Oktoberfest Lager
Fermenter 5 - Belgian Dubbel
Fermenter 6 - Raspberry Mead

Do you need a computerized solution or just a controller ? There are stand alone controllers that are fairly easy to wire up. The computerized setups take a little more effort, but they allow more versatility too.

What do you require ?

Either would be fine. I could manually enter the data or use a "recipe" that iI could store in the computer. Easy sounds nice, but the computer may provide more versatility. I was looking on the web today at PLCs. Thanks for the reply. Greg

PLCs are overkill.

I've used ADC cards with PCs before, but I think there are serial and USB devices now. I haven't looked because I generally use a microcontroller.

The real issue with using a computer is that someone needs to write a User Interface to tell the peripheral to turn on and off or to read the temperature.

All you need to control a power device (pump, heater element, etc) is a "peripheral" with a 5V output and then a Solid State Relay. They can be controlled with 5V.

Getting temp into the computer requires an Analog to Digital Converter channel, one for each sensor. And then just use a thermistor which will give you temperature as a 0 to 5V signal.

I have purchased the auduino microcontroller board for $32 for use in my own system. It is designed to be used by non technical people like musicians and artists. I have not yet used it myself.

http://www.sparkfun.com/commerce/product_info.php?products_id=666

I will be sharing the code I write for the GUI and the microcontroller, when I write it.

I likely am crazy to want to set up a automated system to control my extraction, but it is a challenge. For some reasons I like challenges. Some people do crossword puzzles, restore rust buckets or climb jagged rocks. I like to brew beer, make cheese and garden.

Does anybody have any other ideas? Does anybody have an operational system? Yes, I know that the system can fail, but there is always the manual override to save the batch. Just give me some ideas that I can let rattle arround in my head. Thanks

Brewman,
I'm curious about the solid state relay. Do you use any interface circuit (for protection) between it and the microcontroller, that you would need with an SCR ... or on the same token, do you need a driver to run it (does the micro provide enough source current).
Interfacing to a PC is really nice through a parallel port, and it saddens me to see them being phased out

I have no personal experience but for the simple approach allot of people use Ranco controllers. Yuri_Rage posted this link awhile ago.

The ranco unit is suitable for a manual system. It cannot be programmed to do the step temperature rises. I would love to see a RANCO type unit that works like my microwave. I can set my microwave along with the temperature probe to maintain 100 degrees for 60 minutes then go to 130 degrees for 30 minutes. Actually, I have been considering yanking the processor out of a microwave and using it for my application.

As for the relays with a PLC, my understanding is that the relays are isolated, but it is recommended that the transformer used on the output device be separate from the transformer powering the PLC.