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Has anyone been able to make Trio EZ Pilot work with a cheap GPS receiver

M

moandor

Member
My RV-6A (I didn't build it) has a Trio EZ Pilot autopilot, but it's not connected to any GPS input. So it's only able to be in wing leveling mode. I have an NMEA0183 GPS receiver similar to this one. According to Trio's manual, the parameters should match (4800 baud, NMEA, 8-N-1, etc.)

After I connect it, the autopilot detects some input (it automatically switches to course mode), but keeps showing "NO GPS". I also have an FP-5L fuel gauge. In MPG mode it shows "on", which means it connects to the GPS receiver, but cannot get the ground speed data. All these behaviors are the same regardless of being on the ground or flying.

I connected the GPS receiver to a computer and read its output. Everything looks alright. Position, ground speed, course, etc. appear in sentences $GPRMC, $GPGLL, $GPVTG and such. But it doesn't have magnetic variation data. Maybe this is the problem?

Has anyone had success wiring a similar GPS receiver to Trio EZ Pilot? Am I doing something wrong or is it just fundamentally incompatible? Thanks in advance!
 
Microcontrollers tend to use “TTL” signals which are 0-5v or 0-3.3v which is probably what your GPS spits out, but most avionics use rs-233 signals which use -15v to +15v which rejects a lot of interference.

Try using an adapter like this and see if your GPS starts working once you are sending the correct signal levels.

 
I think my GPS is using RS232. The voltage between the tx pin and ground is negative as measured by a multimeter. I also used an RS232 to USB adapter like this to connect it to a computer.
 
Would it be that the gps puck is only giving position data out? The Trio head is looking for a gps generated course line (flight plan line) to follow.
 
Yea the GPS has no flight plan information. So I expected the autopilot to enter "NO FPLAN" mode and can only operate in course mode. I should be able to give it some course degrees and it keeps flying in that direction.
 
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