Buying an Arduino Chip, which to buy for my project needs?

I am working on a prototype of a moving-head yoke stage light. I want to control the tilt and pan of the unit with an Arduino built into a computer (for color control, etc.) of ZBOX size (small desktop computer, about 3"x10"x10"). I want the Arduino to talk directly to a Linux system, which will have software of some sort running on it to tell the Arduino to move the motors. As of now I have no Arduino programming skills, but want to pick something that will work for me. I also want to display motor positions (1 line per tilt and pan) on a small LCD, mounted on the side of the computer (won't be on the chip as a shield component, will need extension wiring).

The chip would be better if it had ethernet or some other low-latency connection to the computer. This is just a prototype, though, so I want something affordable, say under $100 for the chip, maybe $20 for the LCD, and $100 total on the two motors. I am looking at using the LED PT105 by Optoma in the project, too.

Budget looks to be a total of about $500.

BTW, I am looking at the Vexta PK266-02A for my stepper motor.

You seem to be confused on what an Arduino is. The Arduino isn’t a chip. It is a Prototyping platform. It consists of an IDE, a core set of libraries, and a board generally called “The Arduino”. The Arduino board is based on one of two ATmega microcontrollers, which have the Arduino boot loader on them.

See: http://arduino.cc/en/Main/Hardware

Most Arduino boards have a USB-to-Serial converter built-in, which is plenty fast to control motor. You can get an Ethernet shield (shields are the name for boards that plug on top of an Arduino board) or the “Arduino Ethernet” which has the Wiznet chip built in. The downside to the integrated “Arduino Ethernet” is it doesn’t have an on-board usb connection, so it requires an separate cable for programming.

Either way though, the Ethernet is connected to SPI and may (or may not) offer better latency than serial.

I would argue going even easier and get the UNO. You could get the motor shield to drive the motors. I haven't ever used one but it should simplify it. You can use a USB cable from the Arduino inside the machine to connect directly to a USB port on the PC itself. There is absolutely no value that I can see of doing Bluetooth or WIFI or any other connection since the Arduino will be physically inside the PC.

Now I would go on to say that once you get an UNO and realize how much fun this is you are going to regret plugging it into your PC and not having it anymore. So you might even take the next step if you have the skills and take the Atmel328P out of the Arduino and put it on a board with the assoicated components. Let me splain that a bit more. Once you have the Arduino doing what you want it to do, you can phyisically remove the Atmel328 from the Arduino UNO board and, with a few support components, put it on its own board. You can then buy another chip to put back in the UNO to use again. The only other real cost would be in the FTDI converter.An Atmel328P with the bootloader installed costs $5.50 on Sparkfun.

http://www.sparkfun.com/products/10524

The FTDI is $14.95 on Sparkfun. http://www.sparkfun.com/products/9716

With the addition of only a couple of capacitors, resistors, and bears oh my! You could have your Micro side running for about $25 and still have your Arduino to play with.