These are the Eagle CAD files for the bGeigie v3.0 (codename NX) board.
This project is a part of the Safecast radiation monitoring project. Find out more on the Safecast website
Note: although the github repo is named bGeigie2, the content is really the bGeigie3.
2011-2013 (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 gerber files can be downloaded here
The full BOM can be found here.
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.
- Wiki entry on microstrips
- Microstrip impedance calculator
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.
- PCB Fusion
- PCB Cart (seems to offer manufacturing too)
- PCB Express