DorkbotPDX people doing strange things with electricity

I've been getting interested in the Parallax Propeller chip lately and decided to dive in by designing a breakout board for the chip. I based my design on the reference designs given by Parallax so nothing really new there. I decided to include an EEPROM chip on the board so that programs could be stored between power cycles.

One of the main reasons I have been interested in gyroscopes and accelerometers is to measure tilt angle for things like balancing robots. So after building Paul's board with the three axis accelerometer and two axis gyro, I moved on to doing the software to use the board to measure tilt.

At the last Monday meeting I picked up a gyro/accelerometer kit from Paul. This is a successor to his accelerometer board which several of us have built successfully. This new board is a more complex build, both because it has two LGA packaged sensors and also because it is pretty tightly packed and almost all of the discrete components are 0603 0402 (I thought they looked small....) packages. I used a couple of single package solder paste stencils (LGA 12 and LGA 16) to put paste down for the two sensor chips and put paste on by hand for everything else.

While poking around Digikey for various sensor chips, I ran across the Freescale MMA7455. This seemed like a really nice 3 axis digital output accelerometer and it only costs $2.00 in single quantities. The specs seemed pretty nice for such an inexpensive chip: SPI or I2C output, 2g, 4g or 8g selectable range, tap, threshold and freefall detect with two interrupt outputs and/or continuous sample mode. So I ordered one and made a quick breakout board on one of the last group board orders. I didn't have a lot of time to get the design together so I made it pretty simple.

It was a good turnout for the open workshop at PNCA on Sunday. Don and Monty both got their hot plate systems up and running and soldered some boards. A couple of others started to put together their temperature controller boards and some questions came up about things I may not have made clear enough before:

The current versions of the Eagle files, .hex files and source code can be found at http://dorkbotpdx.org/blog/scott_d/temperature_controller_board_final_design

To install the temperature controller software on a new ATMega328 you can either load the .hex files or build from the Arduino source code. If you choose to load the .hex files, you should load both the temp_control.hex which is the program code which should be loaded into flash memory and also eeprom.hex, which contains some parameters for the controler which reside in eeprom memory.

I populated one of the temperature controller boards, did some testing and then loaded the PID software and tried out the IR sensor. So far, everything seems to be working. I don't have any of the thermocouple chips to try out so that will have to await the next parts order. But so far, so good. I'll be happy to help anyone get their board built out and running.

Edit-

The temperature controller PC boards have arrived. I was amazed at the interest. In the end, fifteen of the boards were requested. There have been a few people who have asked for them since the order was placed so I'll probably do another order of the boards in the next PCB order.

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.

I've done a quick first pass on the PCB design for the temperature controller. There are a few things I'd like some feedback on: