FF-1 GPS connection issues

[sprightlyone]

hi
i fiited the FF-1 to my aircraft but did not connect the GPS interface 1st
later when i connect the GPS reciever no connection
i have the units checked & find i need an interface to get the GPS to connect to guage is this normal ( not mentioned in manual )
do i have a faulty guage ??
what is the fix for this problem
has anyone tried & had issues as described
let me know your experience
lyle

[rainier]

Make sure your GPS is ternamitting NMEA, that you have both the correct pins on the GPS and FF-1 and also have a ground connection between the two. You only need the GPS TX to the NMEA (GPS) input of the FF-1. Make sure you have selected the same baudrates on the devices - if different they certainly will not talk. If your GPS allows multiple formats - choose NMEA.

[sprightlyone]

hi rnainer
thanks for your reply
let me explain the problem they both are NMEA capable it is just that gauge is NMEA CURRENT MODE LOGIC & the GPS Reciever is 5V LOGIC
i had an electronics engineer identify the problem & bench test an interface to let them talk to ea other this worked but he was unable to get the interface to work reliably once he built the final version to re-install in my plane
i hope i haven`t confused you further
i just need to know is my guage faulty of can i buy another GPS reciever that will output the NMEA string in CURRENT MODE LOGIC rather than common 5V LOGIC
thanks lyle

[rainier]

OK you are then using a naked GPS chipset module. These output TTL logic. Signal is inverted and swings from 0 to 3.3V (or 5V for older modules).
We do not make anything that would interface directly to this as this is not the norm for commercial GPS sources. These output NMEA using RS232 signal levels. You would have to use a converter - there are many available from hobby shops, DIY kits etc. Usually based on a MAX232 chip or one of the many copies. These take in TTL logic and output correct RS232 levels.

Since you are only transmitting you can get away with just a simple NPN transistor or low gate voltage N-FET and a pull up resistor to your GPS power supply. The receiver in the FF-1 will accept a voltage below about 0.5V as "low" and anything above about 2V as "high". Your transistor will take care of the inversion.

[PaulSS]

Wouldn't you be better off just buying something like this?

https://www.amazon.co.uk/Waterproof-Nav ... s9dHJ1ZQ==

[rainier]

That's a USB variant, does not output NMEA over RS232. It sends NMEA formatted data over USB protocol. Not a simple task to get RS232 out of that.

More like this one:

https://www.amazon.com/GlobalSat-BR-355 ... JFUO&psc=1

[sprightlyone]

hi all those interested in my problem
this is the gps reciever i am trying to use :Garmin GPS18x LVC OEM Serial GPS (bare wire )
there is 3 variations listed on website Garmin GPS18x PC OEM Serial GPS (serial plug & pwr supply)
Garmin GPS18x USB (USB plug)
Garmin GPS18X-5HZ (????? termination )
so if the garmin is not compatable with this guage which australian available receiver will connect to the supplied wiring & work ?? out of the box
ck am i stuck with buying an interface to make it work (i tried the simple way would work on bench test but the moment circuit was moved it stopped working i don`know & can`t find why it stopped working ) will an interface give me the same grief ??
your support is appreciated
lyle

[rainier]

Serial = RS232.

usually...