The Big Avionics Upgrade
Part 6 - Ones and Zeroes
In the last chapter, I had completed the design
for the audio interfaces. This could be thought
of as the man-machine interface. In this part, I
want to explain the machine-machine interfaces.
The decisions about how data flows across the
airplane between the boxes.
Apology to the reader: Between the time I
started and finished writing this chapter of
the story, I learned things I didn’t originally
know. I will try to tell the story as it happened
(as I experienced it, as it felt) changing the
details only to avoid presenting the reader with
information that later proved to be false, but
still not breaking the timeline of the story. We
rejoin our ignorant hero at Avidyne…
The Avidyne IFD-540 is advertised as having
all of the capabilities of a Garmin GNS-530W
plus a few more. The first interface that was
of interest to me was the ability to slave my
portable GPS to the panel mounted unit for
the active flight plan. In my case, there were
actually two portable units; the 696 on my yoke
and the 396 on Bethany’s side of the panel.
But I also wanted the ability to break that link
at will. I wanted to be able to separate the
portables to play “what if” with the flight plan
without disrupting the official version and/or
preserve the flight plan in the case of a failure
(electrical or otherwise) within the panel. The
easiest way to accomplish this is with a toggle
switch, but I reaped another benefit. On the
other side of that toggle switch I wired up
the traffic data flowing out of the NavWorx
ADS600-B. The two data formats are different,
so flipping the switch alone only breaks the
link. To change data types, I also have to
change the input type from the Garmin main
menu, in addition to flipping the switch. With a
little practice, it only takes a moment.
The Avidyne IFD-540 also has the ability to
interface with a fuel computer. The data from
the IFD-540 is the same data that goes to the
696 and 396 selector switch. There is also a
data line going the other direction, taking fuel
data into the IFD. My airplane is equipped with
an engine monitor, but I do not have the fuel
flow option installed (yet). I installed H