SatPointer

Antenna rotator controller that automatically points a dish to track satellites. Uses a BNO085 IMU (9-axis inertial measurement unit) for absolute orientation sensing combined with PID control to drive stepper and servo motors.

Overview

ESP32 antenna controller that tracks satellites using BNO085 IMU + PID control. Accepts positioning commands via Easycomm II protocol (rotctld compatible).

Hardware

• Microcontroller: ESP32
• Sensor: Adafruit BNO085 (I2C)
• Azimuth: Stepper motor (GPIO 18/19)
• Elevation: Servo motor (GPIO 16)
• Link: Serial over USB at 115200 baud

How It Works

1. BNO085 measures antenna orientation (quaternion → Euler angles)
2. Manual north offset set via SETNORTH command
3. PID controller compares desired vs. actual angles
4. Motors adjust antenna to target position

Getting Started

North Calibration

Manually set north reference when powered up:

SETNORTH        - Set current direction as north (0°)
SETNORTH 45.5   - Set north offset to specific angle
RESETNORTH      - Reset offset to 0°

Point antenna at true north (compass/sun position) and send SETNORTH.

Communication

Easycomm II Protocol

Query current position:

AZ     → returns "AZ123.5"
EL     → returns "EL45.2"

Command new position:

AZ180.0 EL45.0

Remote Operation with rotctld

Start rotctld on your antenna controller:

.\rotctld.exe -m 204 -r COM1 -s 115200 -T 127.0.0.1 -t 4533

Then use rotctl or compatible software (Satdump) to connect:

rotctl -m 204 -r TCP:127.0.0.1:4533

Tuning

PID gains are configured in main.cpp:

// Azimuth control
float azKp = 8,     azKi = 1,   azKd = 0;

// Elevation control  
float elKp = 0.5,   elKi = 0,   elKd = 0;

Tuning tips:

• Kp (Proportional): Larger = faster response, too large causes oscillation
• Ki (Integral): Helps eliminate steady-state error
• Kd (Derivative): Dampens oscillations, reduces overshoot

Sensor Outputs

The BNO085 provides multiple orientation estimates:

• Rotation Vector (SH2_ROTATION_VECTOR): Most accurate, uses all sensors
• Geomagnetic RV: Lower power, mag + accel only (no gyro drift correction)
• Game RV: Gyro + accel only (no magnetic field reference)

Currently uses Rotation Vector for best accuracy in satellite tracking applications.

Future Enhancements

• Add magnetic declination correction for true north
• Calibration status LED indicators
• Data logging of tracking accuracy
• Support for multiple antenna types (parabolic, Yagi, etc.)

References

• BNO085 Datasheet
• Adafruit BNO08x Library
• QuickPID Library
• [Easycomm II Protocol Specification](http://www.dk1tb.de/rotor/easycomm.html and https://github.com/Hamlib/Hamlib/blob/master/rotators/easycomm/easycomm.c)