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Old 08-11-2017, 02:12 PM
leok leok is offline
Join Date: Apr 2013
Location: Clarkston, MI
Posts: 435
Default Electrical System Design and Build continued

I mounted all switches to small individual sub panels in functional groups. Each switch sub-panel has connectors so they can be removed and worked on the bench.


Next comes the Avionics

Design Step 3 - Avionics

The most complex section of the electrical design is cross connecting the avionics. After identifying the avionics, the task of designing, documenting and otherwise figuring out the required connections can be overwhelming. This is where the information learned in the G3X installation class really helps. I divided this section of the design in two parts as well, communication and power feed. The following is the process I learned and followed;

Start with a ‘Communication Diagram’ of all avionics and communication paths. What needs to talk to what, and how they talk. There are examples in Section 2 of the G3X Installation Manual downloadable from the Garmin website. In my case, I chose all Garmin avionics, others would be similar but different based on their unique features. Garmin uses a CAN network, RS 232, A429 and Ethernet to communicate between boxes, depending on the specific box. Downloading the installation manual for each box, and of course, reading the technical description, will tell you what is needed.

1) For the Garmin CAN, using a simple line drawing of the aircraft, I established a diagram of the approximate locations of all avionics that use CAN to communicate. The CAN structure is a daisy chain with terminators (120 ohm resistors) at each end. Each link is numbered in turn giving an identifier for tracking purposes. We learned in our class that for Garmin, using the GSA28 autopilot servos as the termination of the CAN is useful as the termination function is built into the device and needs only a jumper.

My CAN chain is as follows:

CAN BUS order


2) Make a box diagram showing each device (Garmin calls these LRUs or Line Replaceable Units) in the CAN network and connect them with a line. Then review the installation manual for each component and determine what else it needs to talk to, or what needs to talk to it, and by what method. You will also need to add several boxes that do not use the CAN network. Most components will use RS232 in addition to or instead of CAN. The GTN650 GPS/Navigator/Com uses a combination of RS232, A429 and Ethernet depending on what it is talking to. Pay attention to how many ports of each type are available for each device (i.e. the GDU460 has 5 RS232 ports). For some boxes several methods are used for redundancy. This info is in the G3X installation manual for Garmin components. Each of these is added to the Communication Diagram.

With the CAN order and the communication diagram complete the ‘pin out’ diagrams can begin. This is where good preparation pays as fixing/changing earlier work takes time to alter the underlying documentation. This is also where the power and ground for each device will get added.
Building started Oct 5th 2014, Flying since 1/16/2020
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Last edited by leok : 06-25-2018 at 03:31 PM. Reason: fix picture links
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