(a) what a Duemilanove can and can not do?
Errr....broad question. It can do logical control of external devices/sensors, interfacing with the PC over a USB port (as a serial device), and that's about it. Though that's quite a lot. Do not intend to use it for high-speed or high-power numerical computation.
(b) how many SSRs can be controlled by one Duemilanove?
The board has 20 I/O pins, though 2 are reserved for communicating with the PC. Of the remaining 18 pins, 6 can be used as analog inputs or as digital inputs/outputs. Now, each digital output can be used to control an SSR.
(c) hot to make it work and play well with a TC?
You will need a thermocouple amplifier like the AD595.
(d) I want to use a PC to drive everything and need to understand the interface.
The basic interface looks like a serial port on both the PC and the Arduino. Look through some of the sample sketches for plenty of examples.
(e) Can the Duemilanove take the TC feed back and display that on my PC monitor? If not how do I get that date to display in real time?
Yes. The TC data can be acquired, sent over the serial port to the PC, and a program running on the PC can read the data from the serial port and display it on the screen.
(f) I will want to use PWM technology to ramp the DC down to my my peltier's over some period bringing them to idle before turning them off so that all the residual thermal energy from the hot side does not migrate into the fermentor. Can a Duemilanove do that? how?
Yes, some of the digital I/O pins are dedicated as PWM pins and the duty cycle controlled with the analogWrite() function. You will need interface electronics to take the low-voltage (0V-5V) low-current (<20mA) output of the microcontroller and amplify it enough to drive the peltier modules.
(g) Can the Duemilanove tell time? more to the point: Can it control a process based on time elapsed?
Yes, the millis() function gives you a running count of how many milliseconds have elapsed since power was applied or the microcontroller was reset.
(h) Can the Duemilanove track and log and display to a PC monitor, in real time, the things it's done over what time periods?
Yes, by transferring data using the serial port as described above.
--
Check out our new shield: http://www.ruggedcircuits.com/html/gadget_shield.html