Production-intent 2-layer motherboard for a smart face-recognition door lock. Status: Review.
Intended Use
Indoor commercial access-control prototype/validation build controlling a 12 V drop-bolt lock and interfacing to an external 3D biometric module and HLK-LD2410C presence sensor.
What the Device Should Do
Accept a protected 12 V DC supply.
Run an ESP32-S3-WROOM-1-N16R8 with Wi-Fi/BLE and native USB programming.
Power-gate a 5 V biometric camera module and communicate over UART.
Monitor a 24 GHz presence sensor and support low-power wake.
Switch a 12 V inductive lock load with fail-safe default-off control.
The validated specification is saved and the schematic build is underway. The corrected design uses valid ESP32-S3 GPIOs, protected/self-powered USB-C, a higher-capacity power tree, and a fail-off lock driver rather than the ineffective pseudo-isolated stage.
The project is now named Smart Face Recognition Door Lock, and I created the validated Project Specification. The schematic build added 71 components and 45 nets, including the ESP32-S3, AP63301 power conversion, USB-C/ESD circuitry, camera load switching and level translation, radar interface, relay/lock driver, buzzer driver, connectors, and mounting holes.
Open items
I could not perform the independent schematic/ERC verification after the build.
The 70 × 48 mm board outline, placement, antenna keepout, routing, and final DRC remain unfinished.
Exact camera and lock current requirements still need confirmation before production release.
Next steps
Independently inspect and correct the completed schematic.
Production-intent 2-layer motherboard for a smart face-recognition door lock. Status: Review.
Intended Use
Indoor commercial access-control prototype/validation build controlling a 12 V drop-bolt lock and interfacing to an external 3D biometric module and HLK-LD2410C presence sensor.
What the Device Should Do
Accept a protected 12 V DC supply.
Run an ESP32-S3-WROOM-1-N16R8 with Wi-Fi/BLE and native USB programming.
Power-gate a 5 V biometric camera module and communicate over UART.
Monitor a 24 GHz presence sensor and support low-power wake.
Switch a 12 V inductive lock load with fail-safe default-off control.
Provide audible confirmation.
Main Features
ESP32-S3 module with 16 MB flash and 8 MB PSRAM.
USB-C USB 2.0 device/programming interface.
Protected 12 V input; regulated 5 V and 3.3 V rails.
JST-XH biometric-module connector.
5-pin HLK-LD2410C connector.
Relay-isolated contact path for the lock load.
BOOT and RESET buttons.
System Architecture
Diagram
Hardware Subsystems
Compute
ESP32-S3-WROOM-1-N16R8. GPIOs unavailable on the N16R8 module because of embedded flash/PSRAM are not assigned externally. GPIO25 from the supplied text is invalid for ESP32-S3 and will be replaced.
Power
The original XL1509 support network is internally inconsistent: the fixed 5 V version does not use the stated 10 k/1 k feedback divider, and the design omits required topology-specific support/protection. Use a documented 12 V-to-5 V buck solution rated for at least 2.5 A peak with datasheet-matched inductor, catch/synchronous stage, and capacitors. The AMS1117-3.3 is replaced by an efficient 3.3 V regulator because its expected dissipation is excessive for a compact commercial board.
USB-C
USB-C is a self-powered USB 2.0 device interface. Add independent 5.1 kΩ CC1/CC2 pull-downs, low-capacitance ESD protection on D+/D-, and VBUS sensing/protection. USB VBUS must not back-power the 5 V system rail.
Biometric Module
4-pin JST-XH: switched 5V_CAM, GND, module TX to ESP32 RX, module RX from ESP32 TX. High-side load switch defaults OFF at reset. Control GPIO will be a valid non-strapping ESP32-S3 pin (target GPIO14 unless final pin availability requires an equivalent change).
Presence Sensor
5-pin 2.54 mm connector: 5 V, GND, OUT, TX, RX. The supplied GPIO33 is not an ESP32-S3 RTC wake GPIO. Presence OUT will use a valid RTC-capable input (target GPIO18) with input protection/level compatibility verified from the sensor documentation. UART pins are exposed for configuration.
Lock Output
12 V switched output through relay contacts, with flyback suppression at the lock connector. The original PC817 stage does not provide true galvanic isolation because grounds are shared and its relay-driver bias is incomplete. Use a robust fail-off relay driver; retain contact isolation but omit decorative optocoupling unless a real isolated supply/domain is added. Size connector, relay contacts, protection, and copper for the actual lock current.
Audio
5 V active buzzer with transistor/MOSFET low-side driver, defined OFF state, base/gate resistor, and inductive suppression if required by the selected buzzer.
Interfaces and Connections
J1: 12 V screw-terminal input.
J3: 5.5 × 2.1 mm center-positive barrel input.
J2: switched 12 V lock output.
J4: biometric module, 5V_CAM/GND/TX/RX.
J5: HLK-LD2410C, 5V/GND/OUT/TX/RX.
J6: USB-C USB 2.0 device.
Power and Runtime Expectations
External supply only. No battery. Low-power operation is desirable when the camera and lock are inactive, but the mmWave module remains a standing load unless separately gated.
Power Tree and Power Budget
Provisional design budget pending exact biometric-module and lock datasheets:
Table
Rail
Load
Typical
Peak design allowance
3.3 V
ESP32-S3 module
200–300 mA
700 mA transient allowance
5 V
Biometric module
TBD
1.0 A provisional
5 V
HLK-LD2410C
~80 mA provisional
150 mA
5 V
Relay + buzzer
~100 mA
200 mA
12 V
Drop-bolt lock
TBD
2.0 A provisional
The 5 V regulator is sized for at least 2.5 A peak. The external 12 V adapter must be at least 4 A until the exact lock inrush and biometric-module peak currents are known; the originally stated 2 A adapter is insufficient if the lock itself can draw 2 A.
Manufacturing and Assembly Expectations
2-layer FR-4, production-intent SMD assembly.
Standard economical fabrication rules where compatible with USB routing and current paths.
Real manufacturer parts with verified footprints; no unapproved placeholder components.
Firmware-Relevant Hardware Requirements
Native USB-Serial/JTAG on GPIO19/20.
Manual BOOT on GPIO0 and RESET on EN.
Camera UART on GPIO16/17.
Camera power enable target GPIO14.
Presence wake target GPIO18.
Lock control GPIO2 and buzzer control GPIO4 retained if final strapping review confirms no conflict.
Outputs must default to camera OFF, lock OFF, and buzzer OFF during reset/boot.
Physical Design Expectations
Board outline: 70.00 mm × 48.00 mm.
Four 3.2 mm non-plated mounting holes; centers 3.5 mm from adjacent edges.
ESP32 antenna at a board edge with datasheet-defined all-layer copper/component keepout; the requested 15 mm clearance is treated as a conservative minimum where space allows.
External connectors at board edges with accessible mating directions.
Important Design Decisions
Preserve the requested ESP32-S3 N16R8 module and external module interfaces.
Correct invalid GPIO assignments and incomplete USB-C circuitry.
Replace thermally weak/internally inconsistent regulator implementation with datasheet-supported power stages.
Retain relay contact isolation but remove ineffective optocoupling unless true isolation is implemented.
Add input fuse, reverse-polarity protection, surge clamp, USB ESD, and defined driver states.
Assumptions
Indoor installation in a protected enclosure.
12 V center-positive adapter or screw-terminal source.
Biometric module UART logic is 3.3 V compatible; otherwise level shifting will be added.
Lock current is no more than 2 A steady-state; final relay/contact/copper sizing requires the lock datasheet.
Connector positions are provisional within the fixed board outline because no enclosure drawing was supplied.
Change Notes
Converted the two identical supplied text files into one validated specification.
Flagged invalid ESP32-S3 GPIO25 assignment and non-RTC GPIO33 wake claim.