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Single board for bento-Geigie v3.0
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BOM.txt
README.md
TODO.txt
bGeigie2.brd
bGeigie2.sch
bGeigie2_layout.png
bGeigie2_sch.png

README.md

Readme

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

License

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/)

Design

Main microcontroller

Atmega1284p.

Power supply

The system is powered by a LiPo battery providing 4.2V at full charge and dies around 3.5V.

Battery sensing

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.

Possible printing services

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