You did not describe what you want to do.

You do not always need a library. You can program a sketch without it  

There are already a few threads with this topic.

Check this:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1235534880

how to get this data shown as GRAPH.

What kind of data and how many values do you want to display on the graph?

I think the Google Charts is a good and easy tool to display data on a chart.

If you have a lot of values (20 or more) I suggest that you send the data over a ethernet shield to a web database (i.e. MySQL). With an additional webscript you can read the data from the database an display it on a website on a internet site or in your intranet.

Try this:

Code:

switch (MenuActual)
{
     case 0:
      do1();
      break;
     case 2:
      do1();
      break;
     //...
          
     case 1:
      do2();
      break;
     case 3:
      do2();
      break;
     //...
}

We (or I, anyway) was talking about feeding a regulated 5V into the "5V" pins on the bottom "power" shield connector

That's not possible because the Duemilanove has a power detection circuit that checks for power on pin Vin. Vin is high if power comes from power jack or from Vin pin.
Otherwise the +5 V is connected to the USBVCC-Signal and the board will be feeded from USB.

There is no more switch to manually switch between USB and external power supply.

Really?  Is that documented/explained anywhere?  I've been wondering how the new power circuit interacted with +5V via the power connector

Technically it works with +5 Volts at the power jack or at the Vin. But the recommended range is from 7 to 12 Volts. The new arduino board uses a low drop voltage regulator. That means the input voltage must be only a little higher as the output voltage (5V).
If you run it with 5 volts it is not in a stable range and you can get troubles with your circuit.

I couldn't find any documentation but I checked the schema how the power supply is implemented.

The Duemilanove is not prepared to run with external 5 Volt. The board can powered from the USB port or from an external power supply connected to the power jack (2.1mm) or the Vin-Pin.

The recommended range of the external power supply is 7 to 12 volts.

If you need a 5 volt version of Arduino then you can use the Arduino Pro.
A Solutions with 5 volt power supply for Duemilanove is only possible if you do some soldering. Only recommend for professionals!

First buy an Arduino board and learn how to use it.

With some external components you should be able to implement your project.

I suggest that you start with a smaller project. At the beginning try to understand existing examples. Later you can start with your project.

There are probably a lot of open questions for your project. I can't give you a bill of material. You have to implement this step by step.

@TchnclFl

If you are not familar with this technology I wouldn't start with writing my on library. I suggest that you use an existing code. As soon as your protoype works you can think about changing the integrated circuit (IC).

Can you post us the schematic how you want to change the output voltage?

Years ago I implement a power supply project like this. But I did not use any special chips for this project. With operation amplifier, power transistor  and D/A converter you can do this also.

If you really want to use this digital potentiometer I suggest to use the AD5206 with the sample code.

Did you configure your LM35 to use the full temperature range?

See the circuit for full range from the datasheet.



You need to add a resistor (R1) in order to use negative output voltages.

The only redundancy is that we use 2 intelligent devices, the computer and the microcontroller with the external sensors.

Both devices work together - the microcontroller collects the sensor data and sends it over the serial port to the computer.

The question is: do we need the computer?

The computer is the presentation part to display the status and the sensor data. Actually you don't need the computer. If you connect a display and some input elements, i.e. buttons, switches, you can implement a stand alone microcontroller board.

Please can you describe how do you want to use the computer to control the external components.

@pracas

you need some intelligent circuit to read and convert the sensor data to a digital signal in order to send it over the serial port.

Instead of using an A/D converter and a multiplexer why not using a small arduino board? I.e the small RBBB (Really Bare Bones Board), http://moderndevice.com/RBBB_revB.shtml

Is there a reason not to use a microcontroller with digital and analog input ports.

In any case you need an external interface to get the signals into you computer.

Take a look at this:

http://www.geocities.jp/arduino_diecimila/obaka/project-2/index_en.html