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The Aviation Plugs can come with 2 to 10 pins, with 2, 4 and 8-pin versions most used in hobby projects. The pin-outs for the various models are shown below.
Aviation Plugs
Designed by Mark Little
The following conventions are used for the plugs for Arduino I/O allocations, but may be altered depending on the project's requirement.

2-Pin Connector

Pin Description
1 Supply +12 Volts
2 Supply Earth

4-Pin Connector

Pin Description
1 Supply +5 Volts (See Note 3)
2 Supply Earth
3 Signal Line 1
4 Signal Line 2

8-Pin Connector

Pin Description
1 Supply +5 Volts (See Note 3)
2 Supply Earth
3 Signal Line 1
4 Signal Line 2
5 Signal Line 3
6 Signal Line 4 (See Note 4)
7 Signal Line 5 (See Note 2)
8 Signal Line 6 (See Note 2)
Note 1: Unless specifically stated otherwise, the signal on each line should be uni-polar in the range 0 V to +5V.

Note 2: Pins 7 and 8 may be used for bi-polar RS-232 transmit and receiver.

Note 3: Pin 1 may be used for a signal line if the +5V power connection is not required.

Note 4: Pin 4 may be used a Signal Earth if required.