Every airplane needs a compass like this one, it's mandatory by FAA/JAR or the more modern version we bought

In flight this is your main heading information.
Some airplanes are equipped with a directional gyro.
It just looks like the compass and is giving you the same information.
However the working is not magnetic as your compass, but a gyro is doing the work.

Both principles have disadvantages
Gyro's are running a way over time and the compass inertia is screwing up the heading.
So by using both people hope to have a better heading approximation.

Gyro systems need an update at certain elapsed flight time.
By using a digital compass module, we can give feedback to the gyro system.

The HMR3000 Digital Compass Module is an electronic compass that outputs heading along with roll and pitch readings. This electronically gimbaled compass gives accurate heading even when the compass is tilted up to 40 degrees. The highly reliable HMR3000 is a completely solid state device with no moving components. It is a low power, small device, housed in a non-magnetic metallic enclosure. It is easy to install on any platform

The HMR3000 consists of three magneto resistive magnetic sensors and a liquid filled two-axis tilt sensor to produce tilt compensated heading data. A microprocessor controls the measurement sequence of the sensors, and all the parameters
that control the operation are stored in an EEPROM. The output sentences of the HMR3000 conform to the NMEA 0813 standard for Marine communication.

We bought the stuff at Digi-key, ( CAS-rating )
They are cheaper than Honeywell and you can order more items.
HMR3000-D21-232 342-1025-ND

HMR3000 have a large field range of ± 1G (± 100 mT), compared to
0.65 G (65 mT); the maximum of earth’s total magnetic field,

Baud rate is user configurable to 1200, 2400, 4800, 9600, 19,200 or 38,400.
We use 19200 which gives good graphics responds.
The only important thing we need is the Heading, Pitch and Roll
$PTNTHPR, Heading,Heading Status,Pitch,Pitch Status,Roll,Roll Status*hh $PTNTHPR,85.9,N,-0.9,N,0.8,N*2C

This is updated 825 times per minute. 13.75Hz

The HMR300 was only intended for compass info, however the roll and pitch info is present.
It's limited to 45 deg. So that's why we still need gyro's in the system!
But it looks pretty fancy.

TEST fase.

1 wiring done.
2 serial data connection tested , works OK
3 USB/ Serial connection, works OK (com 255 is not working com<10)
4 WJW is developing the raw program sub structure for this.
GPS variation/Calculated according WMM 2000 model or IGRF
Stabilized roll and pitch angles.
Warnings at normal flight banking (30 deg)
Warnings at sensor limits (45 deg)
Output file : heading, roll, pitch for data log system

Inclination , Declination, Dip angle, Variation ?
What are they talking about ??