Ideas, Feedback, and Compatibility on a Heated Build Platform Controller

I've been working on designing and building a heated build platform controller that would work as a standalone device, as well as integrating into the RepRap or Makerbot electronics. It's meant to control up to 400VAC and about 1000W of power using an optically isolated triac which is also protected by a changeable fuse. Temperature feedback is through a Type-K thermocouple being read by a MAX6675. The whole system is controlled by an ATMega328 based Arduino in a TQFP package. Feedback to the user is through a 16x2 LCD and 3 buttons. This LCD could also be used as a general system LCD with the electronics, giving feedback about the various systems that are running (i.e. temperature, build progress, etc.) As well as being used for controlling heated build platforms, it could also be used to control reflow ovens and reflow plates. It will support programmed heater profiles, as well as communications with the motherboard for temperature settings.



I am considering selling this as a kit for the Makerbot, RepRap, and any other RepStraps that may want to use it if I get enough interest. I want to fully develop it and test it first though.

The current version of the board can be found on Thingiverse.
[www.thingiverse.com]

The first version has been prototyped and built, and is currently being tested, so far with great success. The problem is that I wanted this board to be usable by as many systems as possible with as few modifications as possible (preferably not any). I also wanted this to work with both the Gen 3 and upcoming Gen 4 electronics. The current system communicates via I2C, which does not work with RepRap. It is also powered using the 4 pin Molex connector from an ATX power supply using the 5 V output from that. This is good for efficiency and somewhat convenience on a Makerbot, but is almost unusable on a RepRap. In addition to this, the temperature is read using a thermocouple, which, while being great for simplicity, accuracy, and temperature range, is very expensive. The thermocouple and reader IC are 25-30 USD alone and while I and some others would use the thermocouple’s features, many others would be just as happy with a Thermistor in its place.

I want to redesign the board to be more accessible and cheaper for many people. So, here are the changes that I’m going to make to the board for the next version:

1. Switch to a 12V input, then regulate down to 5V using a 7805 regulator
2. Switch to RS485 for communication with the motherboard (with a separate header for RepRap)
3. Remove the Molex connector and replace with screw terminals
4. On the Makerbot electronics, power from the Cat5 cables
5. Add the ability to use a 100K Thermistor instead of the thermocouple
6. Allow for a heat-sink on the triac
7. Small layout changes and better silkscreen

Here is the current schematic (the image is gigantic):
Schematic V0.3

Uploaded with ImageShack.us

So, my question to you is, what do you want in the board? Are these changes enough/too much? What things need to change to be the most useful? And most importantly, do you think that you would use this?