Temperature Controller Board Design (second pass)

Submitted by scott_d on Fri, 2010-02-26 11:02

I've done another iteration of the temperature controller board. I decided I really wanted to provide mounting holes and that caused me to rearrange the board layout a fair amount. I decided to try to get most of the components on the side of the board which would be covered up with the LCD (assuming you put a female header on the board to plug the LCD into). The image shows a standard 16x2 LCD part from the Sparkfun library (the big rectangle) and how it would fit onto the board. The right side of the board, which is not covered by the LCD, contains almost all of the I/O pins so they are unobstructed for running cables and/or plugs. I decided to keep the (optional) thermocouple input pins near to the MAX6675 thermocouple interface chip (on the left side) to have short runs onto the board and to the MAX chip.

I also kept all of the SMT parts from the last iteration. For those who don't want to do much hand soldering of surface mount parts, there are a few choices. For example, you can get a completely functional IR based hotplate setup by leaving off the regulators and the thermocouple interface. You would then either have to provide 3.3V and 5V power or just 5V and use the existing battery in the IR unit. If you do this, you only have three 0805 discrete components to solder and this is only slightly more difficult than building a Dorkboard at a Cult Induction. And , of course, I'll be happy to help anyone reflow the surface mount parts onto their board. Along those lines, I would like to either build or help build one board when they come in to make sure everything is OK. So if someone wants to volunteer their board to be the test, let me know. At this point, I'm ordering 12, all of which are spoken for.

The current software I'm running on my version of this board uses too much SRAM to fit onto an Atmega168 so I'm running it on an Atmega328. I'm pretty sure things could be pared down to fit on a 168 (right now it is an Arduino sketch which uses several libraries). But for the price difference between a 168 and 328 it isn't worth sweating over. However since Atmega328p chips seem to be hard to get currently, this will be an issue for building the boards right away. Unless someone has a stash of Atmega328p chips...

I've attached the Eagle files for this version. The board measures 2x1.7" so the cost to fab is about $5.70 each. Let me know if you have any suggestions on changes to this design. Otherwise, I'll send it along to Laen.

Eric was kind enough to go though my layout and clean it up. It looks much nicer now so I've attached his version to the post above as tempcontrol_mount2.brd.