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Automatic Door Locker (Locki)

actuator NEMA 17 Stepper + TMC2209 controller Raspberry Pi Pico (RP2040) gear reduction Compound Spur (5.4:1) CAD SolidWorks 2024

A universal retrofit smart lock designed to mount directly over standard deadbolt turn knobs without modifying the door. Combines a 3D-printed high-torque gear train, custom Altium power circuitry, and MicroPython firmware with sensorless stall homing.

CAD Assembly — Full enclosure with custom deadbolt adapter

Locki Retrofit Smart Lock — Assembled device overview

Exploded View — Internal gear train, stepper motor, and chassis mounting

SolidWorks CAD — Case knob slot designed to mount directly over standard deadbolts

Deadbolt Knob Engagement — Torque transfer interface

Altium Schematic — Dual battery-powered or 12V DC input with LM2596S regulator

Altium Schematic — INA219 power monitor and TMC2209 driver interface

[01/08] CAD Assembly — Full enclosure with custom deadbolt adapter

Engineered a high-torque compound gear train in SolidWorks delivering 5.2 Nm stall torque to reliably actuate stiff commercial deadbolts.
Routed a custom 2-layer PCB in Altium integrating an LM2596S buck regulator, INA219 current monitor, and TMC2209 silent stepper driver.
Implemented sensorless stall detection on the RP2040 Pico to automatically detect mechanical end-stops without noisy physical limit switches.

01Mechanical Design & CAD Assembly

Comprehensive SolidWorks 3D CAD modeling, multi-body kinematics, tolerance stack-up analysis, and assembly architecture.

01.1 Retrofit Smart Lock Enclosure & Adapter CAD

Full SolidWorks CAD assembly of the smart lock housing designed to retrofit over existing residential deadbolts without door alterations.

[01/02] CAD Assembly — Full enclosure with custom deadbolt adapter

01.2 Internal Gear Train & Drive Assembly CAD

Exploded assembly detailing high-reduction planetary gear train, NEMA stepper motor mount, and reinforced chassis plates.

3D Printed Prototype — Chassis layer and mounting interfaces

[01/02] Exploded View — Internal gear train, stepper motor, and chassis mounting

02Prototyping, 3D Printing & Fabrication

Rapid prototyping iterations, slicing optimization (Bambu Studio / PrusaSlicer), material selection (PLA / PETG / Carbon Fiber), and precision fit checks.

02.1 Deadbolt Knob Engagement & Torque Interface

3D printed torque transfer hub slotted over standard deadbolts with optimized gear tooth profile for high-torque lock engagement.

[01/03] SolidWorks CAD — Case knob slot designed to mount directly over standard deadbolts

03Electrical, Firmware & Hardware Integration

Schematic capture, PCB routing, sensor interfacing, actuator control, and embedded firmware implementation.

03.1 Altium Schematic, Power Regulators & Driver Interface

Altium Designer circuit schematic integrating LM2596S step-down regulator, INA219 current sensor, and TMC2209 silent stepper driver.

[01/02] Altium Schematic — Dual battery-powered or 12V DC input with LM2596S regulator

03.2 Perfboard Circuit Assembly & Pico Stepper Firmware

Custom prototype circuit bring-up and Raspberry Pi Pico firmware controlling stall-detection homing and battery-conserving sleep cycles.

Physical Bring-Up — Breadboard testing of motor homing and current limiting

[01/02] Custom Perfboard Circuit — TMC2209 driver and Raspberry Pi Pico integration