How to debug GPS/Compass

Building a boat with a Matek F405-HDTE, and BN-880 GPS/compass, connected to RX5/TX5, just like the quick start guide shows (configured for Serial3, which is RX5/TX5, baud rate 38400). I see the compass is functional by looking at the Yaw, but when I try to calibrate the compass, the calibration never finishes, and the data screen shows “Prearm: Compass calibration running”, and “GPS: No GPS”. The GPS has both a flashing red light and a flashing blue light.

Could the baud rate be wrong? If I get compass data, does that mean anything? It is mounted in the correct orientation, I can tell by the compass bearing compared to the vehicle orientation. I see in the instructions it says to have good GPS lock

Last night I waited about 45 minutes, and still didn’t get a GPS lock. I am guessing maybe GPS: No GPS means it can’t detect a GPS at all? If it detects the GPS and the GPS hasn’t acquired satellites, I am guessing it has a different message? And the Data/Status screen, if the GPS is alive at all, I would get gps-related values in that screen, or does it need to start acquiring to populate that data? I did notice that if I start Mission Planner without ever connecting, the gpstime is 1/1/0001, and if I connect, the gpstime is 1/1/1970.

I noticed last night that some of the solder joints were left a bit empty, so I reflowed them really well this morning, but it hasn’t changed anything. I am not sure which direction to go with this.

What can I do to debug?


Check wiring first. Make sure you haven’t mixed up RX and TX. “NO GPS” means it is not detected at all.

When calibrating the compass, it helps to have a good GPS lock as you mention, and make sure you are outside and away from all sources of magnetic interference.

This doesn’t necessarily mean the compass is working. Yaw will change from the Z-axis Gyro. Is there an LED flashing on the GPS/compass module? Is there a device ID showing in the parameters for a compass or in Mandatory Hardware>Compass?

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Thanks, Yuri_Rage, TX/RX swap did the trick. Next stop - compass calibration!