Arduino ELS V1.0

Electronic leadscrew firmware for a small lathe using an Arduino Nano/Uno-class ATmega328P board, spindle encoder, stepper driver, and 16x2 I2C LCD.

The firmware supports synchronized threading, spindle-synchronized feed, a simple cycle mode, backlash-aware return moves, calibration, EEPROM settings, and a one-knob/one-button user interface.

Status

This is working firmware, but it controls real machine motion. Treat it as experimental until it has been tested on your exact lathe, encoder, stepper driver, motor, power supply, and wiring.

The current sketch compiles for arduino:avr:nano:

Sketch uses 29682 bytes (96%) of program storage space.
Global variables use 1078 bytes (52%) of dynamic memory.

Features

• Threading mode with TPI or metric pitch input.
• Feed mode with signed feed direction.
• Cycle mode with synchronized forward feed, dwell, return, and creep-to-start.
• Spindle quadrature direction from encoder A/B.
• EEPROM-stored settings with startup sanitization.
• RPM limit trip.
• Calibration routine for steps/mm correction.
• 16x2 LCD diff rendering to reduce I2C traffic.
• One rotary encoder with short/long press controls.
• Optional serial bench UI for testing.

Hardware

The code is intentionally ATmega328P-specific. Timer1 and direct port writes are used for deterministic step timing.

Function	Arduino Pin	Notes
Spindle encoder A	D2 / INT0	Interrupt on rising edge
Spindle encoder B	D4	Sampled for direction
Stepper STEP	D9	Direct port output
Stepper DIR	D8	Direct port output
Stepper ENABLE	D10	Active low by default
UI encoder CLK	A0	Pullup input
UI encoder DT	A1	Pullup input
UI encoder switch	A2	Pullup input
LCD SDA/SCL	Arduino I2C	16x2 I2C LCD at 0x27

Default assumptions:

• Board: Arduino Nano/Uno, ATmega328P, 16 MHz.
• LCD: 16x2 I2C backpack at address 0x27.
• Stepper driver: STEP/DIR/ENABLE style driver.
• ENABLE polarity: active low.

Safety

This firmware can move a lathe carriage. A software bug, wiring fault, wrong setting, missed step, missed encoder pulse, or driver fault can crash the machine.

Before using it on the lathe:

• Test with the stepper driver disabled or mechanically disconnected.
• Test with the motor unloaded.
• Verify carriage direction in every mode.
• Verify spindle encoder direction.
• Verify encoder PPR, leadscrew pitch, microsteps, belt ratio, and calibration.
• Verify the RPM limit.
• Verify emergency stop behavior.
• Keep a physical emergency stop in the motor power path. Do not rely on the Arduino as the only stop.

See docs/SAFETY.md and docs/TESTING.md.

User Interface

The UI uses one rotary encoder with a push button.

Core rules:

• Rotate: move left/right through choices or change the selected digit.
• Short press: select, start, confirm, or advance to the next digit.
• Long press: stop, cancel, back, or menu.

Standby:

• Rotate selects THRD, FEED, or CYCL.
• Short press enters the selected mode.
• Long press opens the menu.

Thread/feed/cycle screens:

• Short press on the action field starts/arms/resumes.
• Short press on a parameter edits it.
• Long press stops active motion.
• If motion is not active, long press returns to standby.

Menu and calibration screens:

• Short press enters/commits the selected item.
• Long press cancels or backs out.

Optional serial bench controls are available at 115200 baud when ELS_ENABLE_SERIAL_UI is set to 1 before compilation:

Command	Action
l	Rotate left
r	Rotate right
p	Short press
lp	Long press

Build

Install the Arduino AVR core and the LiquidCrystal_I2C library, then compile for Arduino Nano/Uno:

arduino-cli compile --fqbn arduino:avr:nano .

The sketch is close to the Nano flash limit, so the serial bench UI is disabled by default. To enable it, set:

#define ELS_ENABLE_SERIAL_UI 1

before the default ELS_ENABLE_SERIAL_UI definition in the sketch.

Repository Contents

• arduino_ELS_V0_1.ino - main firmware sketch.
• docs/SAFETY.md - machine safety notes.
• docs/TESTING.md - pre-cut testing checklist.
• docs/UI.md - UI behavior summary.
• CHANGELOG.md - release notes.
• LICENSE - MIT license.

License

MIT. See LICENSE.