Pan-Tilt System with Joystick Control :: ATMega328P

Project Overview

This project implements a simple pan-tilt mechanism driven by two stepper motors, allowing manual control via a 2-axis analog joystick. Users can adjust the azimuth (pan) and elevation (tilt) using joystick movements. A button on the joystick resets the system to its centered position. Additionally, orientation can be controlled via command-line input through a serial interface.

The system is built around an ATmega32 microcontroller and uses a custom hardware abstraction layer (avrhal) to manage stepper motors, ADC, USART communication, and joystick input.

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Features

• Hardware-level control of stepper motors using A4988 stepper drivers, managed through custom abstraction
• Precise positioning of the pan-tilt mechanism with an accuracy of 1° in both azimuth and elevation axes
• Manual control via a 2D analog joystick (X/Y axes) for intuitive real-time positioning
• Position reset function via joystick button to return to neutral (centered) orientation
• USART interface for remote control and feedback, compatible with EasyComm2-style commands
• Interoperability with rotctl and Gpredict, allowing for automatic satellite tracking
• Low CPU overhead, with motor stepping handled by hardware timers (no pin toggling in interrupts)
• Command-line control via serial terminal (e.g., minicom) to issue commands or monitor system status

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Hardware Setup

• Microcontroller: ATmega328P
• Motor Control: 2x stepper motors with A4988 drivers
• Joystick: 2-axis analog joystick with integrated pushbutton
• Communication: USART @ 9600 Baud, 8N1
• Custom HAL:
  • Stepper motor control
  • ADC input for joystick
  • USART serial communication

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Dependencies

• AVR Libc (avr/io.h)
• Custom AVR Hardware Abstraction Layer:
  • avrhal/stepper.h
  • avrhal/joystick.h
  • avrhal/usart.h
  • avrhal/adc.h
  • avrhal/commandParser.h
  • utils/bit.h

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Usage Instructions

Manual Control (via Joystick)

1. Move joystick left/right – controls horizontal panning (azimuth)
2. Move joystick up/down – controls vertical tilting (elevation)
3. Press joystick button – resets both motors to their zero (center) position

Remote Control (via USART)

Connect to the device using a serial terminal (e.g., minicom) at 9600 Baud, 8N1. The following commands are supported:

Query Commands

• STATUS
  Prints detailed stepper status and current angles in the format:
  P:<taken>/<remaining> T:<taken>/<remaining> p:<azimuth> t:<elevation>

• AZ
  Returns the current azimuth angle (in degrees):
  AZ<value>.0

• EL
  Returns the current elevation angle (in degrees):
  EL<value>.0

Position Commands

• AZ<value>
  Sets the azimuth to the specified angle (integer degrees).
  Example: AZ45

• EL<value>
  Sets the elevation to the specified angle.
  Example: EL30

• AZ<value> EL<value>
  Sets both azimuth and elevation in one command.
  Example: AZ90 EL45

Note: Commands are case-insensitive and must be followed by a newline (\n) or carriage return (\r\n) when sent over serial.

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TODO

• Implement different microstepping modes (currently only full-step is supported) for finer orientation control
• Refactor stepper logic to use two independent hardware timers for better per-motor speed control and increased flexibility
• Add limit switch support for physical range detection and homing
• Add EEPROM storage to retain last known position across power cycles
• Optional: Integrate OLED or LCD for local display of position or status

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Credits

• CAD Model Design:
  Original pan-tilt CAD model by Scienteer

• FreeCAD Conversion:
  Converted to FreeCAD format by Eyal Abraham