This is the Eagle CAD files for the bGeigie v2.0 (codename Delta) board.
This project is a part of the Safecast radiation monitoring project. Find out more on the Safecast website
2011 (c) Robin Scheibler Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) For more details see (http://creativecommons.org/licenses/by-sa/3.0/)
The system is powered by a LiPo battery providing 4.2V at full charge and dies around 3.5V.
The Atmega1284p has two internal analog references: 1.1 or 2.56.
We need to sense the battery voltage between 4.2 and 3.5V.
Let's use a voltage divider with R1 = 100K and R2 = 120K.
Then Vs = R2/(R1+R2) = 0.54*Vin, giving a range of 2.3V to 1.89V roughly. We decide to use the 2.5 reference. This gives use roughly 170 levels of resolution.
50 Ohm trace for the Radio and GPS antennas
As a starting point, I used the following values based on PCB Fusion.
- Trace width: 2.815mm (need to look-up tolerance of printing service)
- Substrate height: 1.6mm (standard from PCB Fusion)
- Copper thickness: 0.035mm (guessed from PCB Fusion characteristics, inner layer ?)
give an impedance Z=50.04 Ohms.