indi-focuser-esp32s3

A low-cost, open-source motorised telescope focuser for Linux, PHD2, and KStars/Ekos.

Built around a 28BYJ-48 stepper motor, ULN2003 driver board, and an Arduino Nano ESP32 (ESP32-S3R8). Controlled over USB from any Linux machine via a native INDI driver. No Windows required. No ASCOM required.

3D-printable motor mounts in PETG are included for three telescopes:

Commercial motorised focusers start at £150 and climb quickly. The hardware in this project costs under £15. Most DIY focuser projects target Windows with ASCOM. This one is built for Linux from the ground up — it runs directly on a Raspberry Pi, a mini PC, or any Debian/Arch machine driving your imaging rig.

This project was inspired by the hardware design of jlecomte/ascom-oag-focuser — an excellent Windows/ASCOM project. The firmware, INDI driver, and 3D files here are independent, original work. See NOTICE for full attribution.

• Any FDM printer
• PETG filament (mandatory for outdoor use — see docs/3d_printing.md)
• ~50g filament per mount

• Soldering iron (for heat-set inserts)
• M3 and M2 heat-set inserts
• M3 and M2 socket cap screws (see each SCAD file for exact quantities)
• Calipers (to verify your focuser dimensions before printing)

indi-focuser-esp32s3/
│
├── firmware/
│   └── oag_focuser_firmware.ino     Arduino firmware (ESP32-S3)
│
├── indi_driver/
│   ├── indi_oag_focuser.h           INDI driver header
│   ├── indi_oag_focuser.cpp         INDI driver implementation
│   ├── indi_oag_focuser.xml         INDI device descriptor
│   └── CMakeLists.txt               Build system
│
├── 3d_files/
│   ├── rvo-horizon-60ed/
│   │   └── rvo_horizon_60ed_motor_mount.scad
│   ├── celestron-nexstar-8se/
│   │   └── nexstar_8se_motor_mount.scad
│   └── skywatcher-explorer-200p/
│       └── sw_explorer_200p_motor_mount.scad
│
├── scripts/
│   ├── oag_focuser_test.py          Serial test and calibration utility
│   └── 99-oag-focuser.rules         udev stable device symlink
│
├── docs/
│   ├── wiring.md                    Wiring guide
│   ├── build.md                     INDI driver build instructions
│   ├── calibration.md               Focuser calibration procedure
│   └── 3d_printing.md               Print settings and assembly
│
├── LICENSE                          MIT
├── NOTICE                           Third-party attribution
├── CONTRIBUTING.md
└── README.md

Arduino Nano ESP32 (3.3V logic)      ULN2003 board         28BYJ-48 motor
────────────────────────────────     ─────────────          ──────────────
D2  ────────────────────────────►  IN1
D3  ────────────────────────────►  IN2
D4  ────────────────────────────►  IN3
D5  ────────────────────────────►  IN4
5V  ────────────────────────────►  VCC  ◄────────────────── motor +5V
GND ────────────────────────────►  GND
                                    OUT1-4 ─────────────►  motor coils

Key points for the ESP32-S3:

• The motor runs on 5V — connect ULN2003 VCC to the board's 5V pin (VBUS), not 3.3V
• The 3.3V GPIO signals are sufficient to trigger the ULN2003 inputs (threshold ~1V)
• Use the D-label pin names (D2, D3, D4, D5) in code — bare integers map to raw GPIO numbers on ESP32, which are different from the silkscreen labels
• The board enumerates as /dev/ttyACM0 on Linux — no CH340 driver needed

See docs/wiring.md for the full pinout table and connector details.

1. Install the Arduino IDE
2. Add the ESP32 board package: Boards Manager → search esp32 → install Arduino ESP32 Boards by Arduino
3. Select: Tools → Board → Arduino ESP32 Boards → Arduino Nano ESP32
4. Open firmware/oag_focuser_firmware.ino
5. Connect via USB-C and click Upload

If the upload fails, double-tap the reset button to enter bootloader mode — the RGB LED will pulse green.

pip install pyserial
python3 scripts/oag_focuser_test.py --port /dev/ttyACM0 --test

Or interactive mode for manual calibration:

python3 scripts/oag_focuser_test.py --port /dev/ttyACM0 -i

Available commands in interactive mode:

Gives the device a stable name (/dev/focuser) regardless of which USB port you use:

sudo cp scripts/99-oag-focuser.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules
sudo udevadm trigger
ls -la /dev/focuser   # should appear

# Debian / Ubuntu / Raspberry Pi OS
sudo apt install libindi-dev libnova-dev cmake build-essential

# Arch Linux / Garuda Linux
sudo pacman -S indi libnova cmake base-devel

cd indi_driver
mkdir build && cd build
cmake ..
make -j$(nproc)
sudo make install

indiserver -v indi_oag_focuser

Connect KStars/Ekos or PHD2 to localhost:7624 and select OAG Focuser. Set the serial port to /dev/ttyACM0 (or /dev/focuser if the udev rule is installed).

The firmware speaks a simple newline-terminated text protocol over USB serial at 115200 baud. Compatible with the protocol used by jlecomte/ascom-oag-focuser, so any tooling built for that project will also work here.

Position is stored to flash on every stop and survives power cycles.

All mounts are OpenSCAD parametric models. Open in OpenSCAD (free), adjust the parameters at the top to match your focuser, press F6 to render, then File → Export → Export as STL.

Measure your focuser with calipers before printing. The key dimension to check per telescope:

Each SCAD file produces all parts needed for that telescope: motor bracket/plate, drive gear, motor pinion, electronics box, and lid.

Print in PETG. See docs/3d_printing.md for full print settings, Bambu Labs H2S notes, and assembly guidance.

See docs/calibration.md for the full procedure. In summary:

1. Set zero at the mechanical end stop
2. Confirm motor direction (reverse if needed)
3. Measure backlash with a dial indicator
4. Test from INDI

Several things behave differently on ESP32-S3 compared to an ATmega Nano. The firmware handles all of these but they are worth understanding:

Pull requests are welcome. Adding a mount design for a new telescope is particularly useful — see CONTRIBUTING.md.

MIT — see LICENSE.

This project is independent and not affiliated with Julien Lecomte's ascom-oag-focuser. See NOTICE for attribution.

Hardware concept and serial protocol inspired by jlecomte/ascom-oag-focuser by Julien Lecomte (DarkSkyGeek). Original work in all firmware, driver, and 3D files.