AXP340/322 ADS-B Transponder - AXP322 AirspeedSwitch

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AXP322 AirspeedSwitch

Printed From: Avidyne
Category: Avidyne General
Forum Name: AXP340/322 ADS-B Transponder
Forum Description: Topics on the Avidyne AXP340/322 ADS-B Transponder
URL: https://avidynelive.com/forum_posts.asp?TID=1288
Printed Date: 26 Mar 2026 at 6:21pm
Software Version: Web Wiz Forums 12.07 - https://www.webwizforums.com

Topic: AXP322 AirspeedSwitch

Posted By: Sanjiv
Subject: AXP322 AirspeedSwitch
Date Posted: 25 Apr 2017 at 6:34pm

Can someone share details of airspeed switch they have used instead of squat switch for AXP install?

Install shows thy axp322 expects Ground (<4v) on pin 19 when on GND.

Most of such TSO switch used to Trigg and BK transponder are Normally Open so those wouldn't work for AXP. Any help with details or links is appreciated.

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PA28-236 @N14

Replies:

Posted By: AUXAIR
Date Posted: 26 Apr 2017 at 4:22am

If I understand your question: The airspeed "switch" is an automatic function, based on GPS speed indications - there does not have to be an external switch activation.

My transponder is in GND when not moving, once I get to 40-50 kts it changes to normal transmit.

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David E.
Cessna 182 RG II

Posted By: oskrypuch
Date Posted: 26 Apr 2017 at 4:26am

Sanjiv is trying to wire in an external electrical squat switch, one attached to the pitot-static lines and triggered by pitot pressure, to drive the GND/ALT switch over.

* Orest

Posted By: flybikeski
Date Posted: 26 Apr 2017 at 8:37am

However he may not know that Avidyne is different than BK and Trigg in that a switch isn't required. To be specific, pin 8 "Weight on Wheels (WOW)" on 540 connector P1001 can be connected to 340 primary connector, pin 5. I think that is all you have to do... I think even the 340 can be set up either voltage high or voltage low on pin 5 for GND vs. moving.

The drawback, a bug really in this whole design, is that when your 540 goes out you lose your transponder too. I lost my alternator in a remote part of Alaska and needed to fly quite a distance to Fairbanks. I could do that easily by shutting most everything off, which really means the 540 has to be off since it takes a lot of power. But when the 540 went off the 340 went to GND mode. So I just ended up turning that off too (then turned both back on when I got near Fairbanks).

Posted By: oskrypuch
Date Posted: 26 Apr 2017 at 10:48am

IIRC, I think that error state behavior may be addressed now.

* Orest

Posted By: Sanjiv
Date Posted: 30 Apr 2017 at 10:54am

Thanks. I have been talking to TEch Support for past days trying to figure out the correct part but we do t have success yet. My unit is already installed based on airspeed switch I had installed in past for KT74, I kept it that way knowing the issues others had with GPS position lost reported as GND. Apparently all others but AXP expects ground signal when airborne and AXP expects ground when actually on ground. Which changed the requirement for airspeed switch to be normally closed and open when triggered. There is no such switch I could find which would do that, not yet. If AXP still supported the configuration as "Active when High", this would be a non issue and I could use existing N/O switch. I hate to take it back to shop to run back pin8 wire from IFD to pin 19 on AXP I believe. But all I am saying is that the issue I have has a simple software config parameter which was taken away in 10.2 and advised it to be set to "avidyne" and under that parameter it's a two step verification, first being GPS reported speed has to be over 35kt then it will look at pin 19 state to switch to ALT mode. So how does airspeed switch or squat switch address the GPS position list issue if it still depends on it? I am confused.

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PA28-236 @N14