FEBEX power delay/control firmware

== Introduction ==

Using an arduino nano to control a FETT which can turna 12V
supply voltage for a FEBEX 3 crate on/off.

GSI FEBEX crates feature a DC-DC converter which provides
12V DC at up to some 20 amps.

However, due to a suboptimal design choice for our
FEBEX Addon Board (FAB), the secondary DC-DCs on the FAB
draw much current during startup, keeping the primary DC-DC
at circa 3V. Rather than throwing away all of our FABs, we
decided to add a PCB between the primary DC-DC board and the
crate backplane.

This new board:

* Charges a big cap (~ 10mF) over a resistor (22R). The cap
  can be discharged over a diode, providing the current boost
  needed for turning our secondary DC-DCs on. 

* Features an arduino nano as a (kinda) component 

* Contains a big FET (Vishay - SI7157DP) which can turn
  the 12V lane between primary DC-DC and backplane on/off

* Measures the input, output and cap voltage with the build-in
  ADC.

* Measures the current using a shunt-resistor and a MAX9611 high-
  side current sensing IC (just becase we can).


When turned on, the firmware waits for the cap to be reasonable full.
As soon as that happens, it turns on the FET, providing the voltage
to the backplane. When the input voltage falls below a much lower
threshold, we assume that we have lost power and turn the FET off
again.

Additionally, a serial connection is provided. Over it, a user can
get read the various measurements as well as power toggle the
backplane. 


== Using ==

For use with the ino tool (http://inotool.org/)

Use make to compile, ino upload to flash the atmega,
and screen /dev/ttyWhatEver 115200 to connect to the
serial interface.

== Remarks on design choice ==

We decided on using a Nano instead of placing a uC directly on the
board because we only needed a few boards, and using off-the-shelf
components when you can simplifies matters.