---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 01/10/25: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 01:42 AM - Re: Re: GPS 175 Wiring Question (David Carter) ________________________________ Message 1 _____________________________________ Time: 01:42:31 AM PST US From: David Carter Subject: Re: AeroElectric-List: Re: GPS 175 Wiring Question I no longer have the 327 in my panel, and don't recall how the previous owner had wired it. From the diagrams, I think you are seeing a difference in approach to logic signaling (auto power on enabled or not) over the course of 17 years of technology evolution (2002 vs 2019). The 327 used an active high (12v) signal on pin 1, the newer gear uses an active low signal on its respective pin. This seems safer to me - one less wire carrying 12v that could short, especially for a non-critical convenience feature like auto on. As wired, I would not think your 327 would come on automatically. Wiring it to ground is like explicitly disabling auto on (versus leaving it floating). It's probably redundant to an internal pull-down that defines the default behavior if nothing is wired to it. Not having a ground wired directly to the unit ground pin is certainly not best practice. I'd closely inspect any wiring done by whoever wired this unit. --- David Carter david@carter.net On Thu, Jan 9, 2025 at 10:39=AFPM farmrjohn wrote: > faithvineyard@yahoo.com> > > Thank you. I guess my confusion comes from the terminology used on the > pin-out diagram and description table where the pin is labeled "in". > > An additional confusion point is the GTX 327 transponder wiring that is > installed. In that instance there are only 5 wires in the harness, but n ot > connected as in the wiring diagram, attached as PDF (transponder works). > As wired, there is an airframe ground connected to pin 1, and a power in > through a circuit breaker to pin 15. The other three wires go to a > Trans-Cal altitude encoder: pin 13 to encoder ground, 14 to encoder power , > and 19 to encoder's RS-232 transmit. The encoder itself has a total of > four wires, the fourth goes to airplane ground. > > Reading note 5, it sounds like transponder pin 1 should be connected to > pin 15 for the auto-on to function. As wired, it does not. Is the > transponder receiving its ground through the encoder or pin 1 or through > the encoder? If thought pin 1, should the auto-on be functional? > > Thanks again, > John > > > david(at)carter.net wrote: > > This is very straightforward as documented. If pin 61 is connected to > ground, auto power on is enabled and the unit will startup when power is > provided on 21 & 42. This is sensing a logic level 0. > > > > > > If 61 is not connected to ground (floating), auto power on is disabled & > you have to power on the unit manually. > > > > > > > > > > --- > > David Carter > > david@carter.net (david@carter.net) > > > > > > > > > > > > On Thu, Jan 9, 2025 at 7:24=AFPM farmrjohn wrote: > > > > > > > > > > I'm in the process of making the wiring harness for a GPS 175 > installation and would like to have the automatic power on feature. I am > confused by the information in the installation manual though and have a > question into Garmin. While waiting for a response I thought I'd ask her e > as well. > > > > > > On the pin-out diagram and the table referring to that pin, #61, it > is listed as an "in". However, on the one wiring diagram that shows pin 61 > it is connected to the aircraft ground and is diagramed as an "out". The > footnote associated refers back the previous section that has it as an > "in". I've attached the portions from the installation manual in questio n. > > > > > > Thanks, John > > > > > > > > > > > > > > > Read this topic online here: > > > > > > http://forums.matronics.com/viewtopic.php?p=515201#515201 ( > http://forums.matronics.com/viewtopic.php?p=515201#515201) > > > > > > > > > > > > > > > Attachments: > > > > > > http://forums.matronics.com//files/gps_wiring_199.pdf ( > http://forums.matronics.com//files/gps_wiring_199.pdf) > > > > > > > > > > > > ========== > > > - > > > Electric-List" rel="noreferrer" target="_blank"> > http://www.matronics.com/Navigator?AeroElectric-List > > > ========== > > > FORUMS - > > > eferrer" target="_blank">http://forums.matronics.com > > > ========== > > > WIKI - > > > errer" target="_blank">http://wiki.matronics.com > > > ========== > > > b Site - > > > -Matt Dralle, List Admin. > > > ="noreferrer" target="_blank">https://matronics.com/contribution > > > ========== > > > > > > > > > > > > > > > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=515203#515203 > > > Attachments: > > http://forums.matronics.com//files/xponder_pins_114.pdf > http://forums.matronics.com//files/xponder_diagram_157.pdf > > =========== =========== =========== =========== =========== > > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.