Flavonoid — 3rd Prototype
3rd Flavonoid Prototype (I2C, ADXL330, On-board Microcontroller)
I jumped a bit ahead and went and designed a board with an ADXL330 tri-axis ratiometric accelerometer, using the on-board A2D converters on an Atmel ATMega32L. It has a USB connection as well, along with a few extra pins connected to the PWM pins of the ATmega32L that I could attach to some three color LEDs. I'm still building the board..by hand. I switched to all 0603 surface mount discretes (at least most of them), which takes small to a whole new level, especially for hand-constructing these things. But, it's fun and a great exercise in careful, detailed craft work. No reflow with the skillet here. I decided to try applying a bit of flux to the tin, and then floating a thing layer of solder on the pads. Placing the super small 0603 surface-mount devices on the pads and applying just a little heat is enough to get a decent solder joint to hold the device on the board. Now, if only everything will work once it's all done!
This board came from Advanced Circuits — I thought I'd try out their $33 board special for the first prototype. Mostly because I wanted something quickly. You can see it comes back bare-bones — no solder mask, no silk..nothing. The lack of solder mask is funky — makes me nervous about areas of the board that are susceptible to solder ball-style shorts.
Here's the board on a test harness to make sure the FT232RL (that chip there) is working. It's the vascular interface between the Flavonoid and the rest of the world — it pumps out the Flavonoid data when you upload yourself to the mothership.
The microcontroller on board, no crystal yet, but it runs using the internal RC oscillator. I was pretty surprised it worked, but I fracked the fuse settings on the first chip. Turns out I can probably set it straight by hooking this chip up to an external clock source — which is how I set the timing fuse, darnit. Anyway, I replaced it and set the fuse correctly to clock from a fast external crystal and it worked like a charm. Flashed the chip with my little test command prompt thing and saw it breathing.
This is basically all finished here. Prototype v03.