AHRS and pressure sensor messages

"Ground test mode" is normal on the ground and clears once you have a good GPS fix and start moving. The "barometric altitude out of expected range" error usually points to a loose AHRS board, so reseat it first.

Both messages come from the AHRS sensors. For setup and calibration, see AHRS on Stratux.

"GROUND TEST MODE - GPS REQUIRED"

The web interface shows this banner, along with "DO NOT USE IN FLIGHT WITHOUT GPS", when two things are true:

  • The IMU (the AHRS motion sensor) is enabled.
  • GPS horizontal accuracy is 30 m or worse, or there is no GPS data yet.

In this state the AHRS is running on its gyros only. It has no GPS-derived corrections yet. The AHRS also gets no GPS corrections while the unit sits still, so small drift on the ground is expected.

What to do:

  1. Put the unit where it has a clear view of the sky.
  2. Open GPS/AHRS on 192.168.10.1 and watch the fix state and accuracy.
  3. Once accuracy is better than 30 m and the unit is moving, the banner clears on its own.

This is not a GPS hardware fault. Only start GPS troubleshooting if the GPS page never shows a fix. In that case see Stratux GPS troubleshooting.

A ground test can also make the AHRS look dead. It needs a GPS fix, the orientation set, and some motion to work properly.

"Barometric altitude out of expected range"

The full text is "Barometric altitude … out of expected range. Ignoring. Pressure sensor potentially broken." Stratux raises it, and ignores that reading, when either of these is true:

  • Pressure altitude is above 70,000 ft.
  • A valid, non-zero GPS altitude differs from pressure altitude by more than 5000 ft.

Ordinary ground differences are far inside that limit. For example, -152 ft pressure altitude against 53 ft GPS altitude is fine.

What to do, in order:

  1. Reseat the AHRS board. The sensors sit on the Pi's GPIO header. A loose board is a common cause of this error.
  2. Power-cycle the unit.
  3. Check that nothing, such as tape or glue, is covering the barometer.
  4. Open GPS/AHRS and check the pressure altitude it reports.
  5. Update to the latest release. A fix for BMP280 problems on a 1.x release is likely in v2.0.
  6. If the error persists, the board may need replacing.

Don't try old versions or the EU edition. The EU edition is the same code with different settings, so it won't help. If you ask for help, say which version you ran before and whether the error is constant or comes and goes.

"Error identifying BMP/IMU"

The AHRS sensors are I2C devices on the Pi's GPIO header, not USB or serial. Stratux looks for the barometer at addresses 0x76 then 0x77, and the IMU at 0x68. It tries again every 4 seconds. A message such as "remote I/O error" usually means no board is fitted or it isn't making contact. Reseat the board.

DIY with a GY-91

A GY-91 module has an IMU and a barometer. Builders have used one in place of the AHRS board, but it is a DIY route. Stratux's sensor documentation lists some GY-91 boards under "Unknown MPU", so detection depends on the board.

  • Hand-wire four connections to the Pi's I2C pins: VIN, GND, SCL and SDA. Check your module's voltage before you pick the 3.3 V or 5 V pin.
  • It has no fan controller.
  • Fix it rigidly, for example screwed to the case. A loose sensor gives poor attitude.
  • Keep tape and glue away from the barometer. Hot glue kept clear of the sensors is fine.
  • Run the orientation procedure afterwards. Point the face that will face forward in flight up when prompted.

Whether other clone boards or different I2C addresses work is unsettled. The current code only probes the addresses listed above.

Still stuck?

Ask in the community and say your version, what the message says, and whether it is constant or intermittent: Discord.