Here is the latest schematic for the Bar End BrakeLight BEBL. Got in the first test ride and it performs amazingly well. The response time seems almost clairvoyant. Ahhh, it feels so good when it stops hurting.
The main change is the power supply fix mentioned in the previous post. The 6V battery I used is this one from RadioShack, but you can find it cheaper on the web. Other changes to note are the power select jumper and the power switch.
The power select jumper allows switching power between the regulated 3.3v from the accel and 5V USB power. This allows the unit to be programmed. The 5V from the USB only powers the micro controller. The 3.3V sensors are therefore protected from the extra voltage. AREF remains connected to 3.3V. I found the switch S2 at Radio Shack. It is perfect. You can access the switch and it stays concealed under the bar. Sweet.