Single board for bento-Geigie v3.0
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README.md
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README.md

bGeigie3

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.

License

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/)

Produce a bGeigie3

Gerber

The gerber files can be downloaded here

BOM

The full BOM can be found here.

Software

Tech notes

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