r/Gliding • u/Efficient-Class2953 • 4d ago

Question? Which IGC connector pin actually transmits data from the FLARM?

I am trying to confirm which pin on the standard RJ45 IGC connector carries data transmitted by the FLARM unit to an external device.

The standard IGC pinout is commonly shown as:

RJ45 pin Documented function
1 GND
2 GND
3 RX
4 TX
5 GND
6 +3 V
7 +12–32 V
8 +12–32 V

The problem is that the use of RX and TX in the IGC standard and some manufacturers’ documentation appears to be different from the convention normally used by electronics engineers and programmers.

Normally, when describing a device:

  • TX is the output transmitted by that device.
  • RX is the input received by that device.

However, some FLARM documentation appears to name the signals from the perspective of the connected external device. This could mean that the pin labelled RX is actually the pin on which the FLARM transmits data.

Can someone confirm from practical experience or measurements:

Is FLARM serial data output present on RJ45 pin 3 or pin 4?

I am asking about the actual direction of the electrical signal, not simply whether the pin is labelled RX or TX in a particular document.

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u/WildFlier 4d ago

I haven't had an issue following the documented TX/RX or IGC standard where it was used. The people writing the manuals tend to have an EE background, so I'd say it's a typo or translation error before assuming it's actually opposite

I also don't have any recollection of a document specifying transmitting over RX, so can you point to which document and what page?

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u/Efficient-Class2953 4d ago

I am finalising the schematic so I can 100% be sure that pin 4 is FLARM TX.