What's new:
03-07-2009: I've finally finished stuffing the new PCB's I got in a couple days ago, and got a chance to post some pics. I'm planning on posting the detailed specs for this board, as well as design files and code in the near future, but for now PICTURES!!!
Description
IT CAN PREDICT RAIN! FIRE YOUR METEROLOGIST!
...jk...
This mote is designed to measure properties of its environment related to the weather. It has built in temperature, humidity, barometric pressure, and ambient light sensors. The barometric pressure sensors are wicked expensive (~$30 each), so I'm waiting on stuffing that part until I get everything else working (I don't want to fry one by accident).
It has a rechargable lithium coin cell batery, and as you can see in the pics, the mote programs and charges via the Irene programming board Prabal designed. The PCB programming header is WAY cool!
Mini Mote vs. Irene
While the board looks pretty identical to the
Irene, it's actually almost completely redesigned (I think a couple footprints are all that I re-used from Prabal's files). The reason for "reinventing the wheel" was to create a sensor-less template board which I could add app specific sensors to later on. As a result of this design goal, I had to rip up everything on the Irene and start from scratch. I even tried to change the PCB programming header outline to coincide with a reasonable layout grid, which turned out to be a HUGE mistake when I got the PCBs back and the programming header didn't fit into the Irene programmer...ARGHAA!!! Nothing an exacto knife can't fix :) Add that to the list of fix-its...
I relocated the EPIC, PIFA, buttons, LEDs, and regulators to optimize space for the template design. I also added a power switch which can be bypassed with a 0 Ohm resistor.
Irene is a 2 layer board and I decided to mimic that aspect when I designed this board as well. Keeping things 2 layer reduces cost at the expense of robustness in design. There are no ground or power planes on the Irene and that makes it really hard to design for things like EMI and crosstalk. In the Mini Mote template I tried to optimize the layout as much as possible such that the side opposite the EPIC module had a large return plane from all GND pins back to the negative terminal of the battery (to reduce loop inductance).
Rev 2 fix-it list (or "how I screwed up bigtime while working on this at 2am"):
1) Fix the PCB programming header so that it actually fits in the Irene programming board.
2) Add the ability to turn off power to the light sensor. I added the light sensor to the design late at night and like a dope, wired it straight up to VCC instead of providing a way to gate power to the TEMT6000. In the words of Homer Simpson: "doh!"
3) Fix a couple incorrect trace widths.
As I find more problems, the list will grow...
