Retrofit BLE Smart Lock

A retrofit BLE smart lock with biometric fingerprint support and 6-month battery life designed for residential indoor doors.

Design Overview

Item	Details
Product Type	BLE Smart Lock
Key Functions	Fingerprint unlock, BLE smartphone app unlock, Retrofit installation over existing deadbolt
Power Source	Li-Ion Battery
Connectivity	Bluetooth
Size	Retrofit over existing deadbolt (inside only)
Environment	indoor
Difficulty	Intermediate
Est. Time	3-5 hours

System Architecture

Power Topology: USB-C 5V → MCU 3.3V LDO

Module List

Module ID	Type	Name	Function	Voltage
POWER	POWER	USB-C Power Jack	Power input	5V
MCU	MCU	ESP32-WROOM-32	Main controller	3.3V

Design Schemes

BLE Smart Lock ★

Key IC selection

main MCU and BLE controller

• Need: Execute biometric matching, BLE protocol stack, and drive the deadbolt rotation mechanism with secure boot support.
• Class: Wi-Fi/BLE SoC with dual-core architecture and hardware crypto accelerators
• Shortlist: Espressif ESP32-WROOM-32 series, Nordic nRF52840 (requires external Wi-Fi or gateway for remote, but ESP32 handles standalone BLE well)
• Pick: Select exact MPN based on Flash size (e.g., 4MB vs 8MB) and operational temperature range (-40°C to 85°C for outdoor/door-mounted resilience).

Power Input & Management

• Need: Accept 5V USB-C input for battery charging or emergency power, and step down to 3.3V for MCU and sensors with low quiescent current.
• Class: USB Type-C interface protection and Buck/LDO power management IC with battery charger
• Shortlist: TI TPS63020 (Buck-Boost for stable 3.3V from variable battery/USB), Microchip MCP73831 (Li-Ion charge management) + Torex low-Iq LDO
• Pick: Select based on battery chemistry (e.g., 1S LiPo vs 4x AA alkaline) and required quiescent current to maximize standby battery life.

Risk register

ID	Area	Severity	Detail	Mitigation
r1	power	high	ESP32 Wi-Fi/BLE peak current spikes during RF transmission can cause brownouts if powered via high-impedance battery configurations or long USB cables during motor actuation.	Ensure adequate bulk capacitance (low-ESR ceramic and electrolytic caps near the module supply pins) and implement intelligent power sequencing to prevent simultaneous motor stall and RF transmission.
r2	mech	high	Retrofit smart locks mounted on metal doors suffer from severe RF attenuation and detuning of the ESP32 onboard PCB antenna.	Ensure the front enclosure or antenna section is molded from RF-transparent plastic, maintaining adequate clearance from internal metal brackets and the existing deadbolt mechanism.

Key Components

2/2 modules matched to real parts. See the BOM tab for the full component table.

USB-C Power Jack (USB4105-GF-A)

The candidate MPN USB4105-GF-A exactly matches the primary MPN and is manufactured by GCT.

ESP32-WROOM-32 (ESP32-WROOM-32)

Candidate 2 exact MPN 'ESP32-WROOM-32' matches the primary MPN and manufacturer 'Espressif Systems'.

Build Summary

• Difficulty: Intermediate
• Estimated time: 3-5 hours
• Tools required: Antistatic mat, Calipers, Magnifying glass, PCB stencil, Solder paste squeegee, Pick-and-place tweezers

See the Build tab for the full step-by-step assembly guide.

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Generated by YuanQi AI Design System · Query: BLE smart lock with fingerprint unlock and 6-month battery life