An S.PORT Compass for FrSky Radio Control Telemetry.

Target audience:

Radio control hobbysts who would like to add Compass telemetry. It can be used with iNav LUA in EdgeTX radios.

Disclaimer:

No Warranty: THE SUBJECT SOFTWARE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY THAT THE SUBJECT SOFTWARE WILL CONFORM TO SPECIFICATIONS, ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR FREEDOM FROM INFRINGEMENT, ANY WARRANTY THAT THE SUBJECT SOFTWARE WILL BE ERROR FREE, OR ANY WARRANTY THAT DOCUMENTATION, IF PROVIDED, WILL CONFORM TO THE SUBJECT SOFTWARE.

In other words: use at YOUR OWN RISK.

License:

Attribution Non-commercial (by-nc)

for the Arduino Nano version:

1. Arduino Nano or Arduino Pro Micro
2. QMC5883L Magnetometer board
3. Dupont Female to Female cables
4. Dupont cable with a Futaba connector on one end and 3 female pins on the other

for the ATtiny 85 version (which requires a custom PCB):

1. ATtiny85 (SOP8)
2. Half height 7.3728MHz crystal
3. (2) 22pF 0805 capacitors
4. (3) 10K 0805 resistors
5. (1) 100nF capacitor
6. (1) FR4 single sided PCB (and etching materials)
7. (5) Dupont PCB male pins (may come included with the QMC5883)
8. (4) 90° Dupont PCB male pins
9. (1) short piece of cable
10. (1) Futaba male to male cable
11. Arduino UNO to be used as an arduino as ISP programmer

Warning: the QMC5883L chip is 3.6V max, so, if you build this project use a sensor like the one in the photos (which has a voltage regulator and works in 5V)

Arduino Nano Connections:

Nano QMC5883L

GND -> GND

5V -> VCC

A4 -> SDA

A5 -> SCL

Nano S.PORT

GND -> GND

VIN -> VCC

D2 -> Signal

The code will work as it is with the unmodified QMC library if you use an Arduino Nano, but you will need copy the attached trimmed version in the sketch folder if you use the ATtiny85 version (do NOT install the QMC library if using an ATtiny85).

If you would like to improve precision, I suggest you analyze the full QMC library, do a calibration and save the obtained data hardcoded in the source code as there is no room for the calibration routine in the ATtiny. You should also add the declination for your location to the code.

CODE: see attached .ino file.

Libraries used:

"S.Port sensor library for FrSky" by Herman Kruisman and "QMC5883LCompass" by MPrograms

To compile the ATtiny85 version you will also need to install the ATTinyCore (by Spence Konde) in Boards Manager

These photos contain the Schematic, PCB (top view), component mount (bottom view), and prototype for the ATtiny85 version.

Please notice there's no room in the ATtiny85 for a bootloader. The lonely pin in the center is connected to the ATtiny's /RST pin and used for the Arduino UNO as a programmer.

ATtiny connections:

ATtiny85 QMC5883L

GND -> GND

5V -> VCC

PB0 (pin 5) -> SDA

PB2 (pin 7) -> SCL

ATtiny85 S.PORT

GND -> GND

5V -> VCC

PB1 (pin 6) -> Signal