Hello Joe,

i would recommend you to do steps:

1) get an Arduino and an RS232 or I2C display (like 4x20) and print 
"hello world" on it

2) get i2c thermomenter ICs fitting for your temp range and get 
temperature values, plus print it on the display.

3) Learn how use the A/D converters by using a potentiometer of lets say 
10kOhm and an analog input. Then develop a transition hardware that 
brings your voltage to 0-5V DC - that is what the Arduino can measure. 
Make sure the output never gets over this values to not destroy the 
Ardino / inputs.

4) Learn how to switch a pin on and off :-) Then develop some drivers 
for your load switchable by 0V/5V /Pin output) that does not load the 
switching pin with more than 20mA.

finally: If you are less experienced, try to go step by step. If you 
fail in the first step, or get unpatient - no need to spend time and 
money for the other steps ;-)

Joerg Z. wrote:
> I was looking for a quick and dirty solution to solve my current needs.

You have 3 options how your project will be:
Quick, cheap and good.
Now please choose any two.

Of course there are ready - made solutions: search for temperature 
switches. But that will not satisfy you i guess because it is not 
exactly what you want.

Joe wrote:
> I am mechnical engineer with very limited knowledge about programming
> and electronics at this stage.
> ...
> What's the easiest way to start?

Cutted from Wikipedia: "Arduino .. aiming to provide a low-cost and easy 
way for novices and professionals to create devices that interact with 
their environment using sensors and actuators."

I have a good knowledge in electronic hardware, but because of simple 
programming and low prices from China I like Arduino!

There are a lot of scripts and samples in the internet, however, as good 
advice (Guest) wrote, you have to spend time about and to work step by 
step.

> Is there a ready-made fan-less box with
> Arduino and display available?

Maybe, I don't know about. As a mechnical engineer you should be able or 
have contacts to build your own housing.

If you are planning to create more, similar projects in the future – and 
want to have a certain degree of flexibility, Arduino might be the 
simplest way to go. It might not be the most professional and it also 
might not be the cheapest possible. But the price tag is adequate, the 
support is outstanding, and because it is mostly based on the well 
established Atmel processor family, you can, in the future, design your 
own, professionally looking boards without the pre-made Arduino breakout 
boards.

It also features a wide band of libraries, so connecting peripherals 
like LCDs, sensors, motors and so on should be as simple as possible. 
Most of the time, you don't need to worry about setting individual pins 
or precise timing. There are very abstracted commands that are as simple 
as Display.init(ENTER, PIN, NUMBERS, HERE); and Display.print("Your text 
goes here"); You should even get that with the most rudimentary 
programming skills.

But if this is a one-time shot, I highly doubt that it would be really 
worth the time you have to spend. Even for me, as a professional 
software developer, it took a few days to really got my first project 
running as expected, for example.

I just discovered this control software which could be very interesting 
using it with an Arduino:
http://iliaslamprou.mysch.gr/index.php/en/about-virtuino

As long as it has enough pins to connect your peripherals, every A. will 
do.

If the price tag is not that important, I would always go for a MEGA as 
development platform. This gives you the most possibilities. If you want 
to implement your project on an actual board later on, you can easily 
port your program to a Uno or Tiny.

André R. wrote:
> I would always go for a MEGA as development platform.

Please remember:
Joe wrote:
> I am mechnical engineer with very limited knowledge about programming
> and electronics at this stage.

So in this state, I would recommend to start with Arduino-Uno as I did 
by myself because most tutorials and scripts in the internet are based 
on Uno.

Later, after the basics were in, I moved to other versions - my favor is 
the Nano.

And for saving ports, my displays I run with I2C interface, from the 
Chinese less than 1 €uro.