Nordic Semiconductor nRF52840
BLE Fingerprint Smart Deadbolt
Overview
A residential indoor BLE smart lock featuring biometric fingerprint authentication and USB-C rechargeable battery, designed as a standard US deadbolt replacement.
Lam Phuong BuiSystem architecture
MCU
SENSOR
POWER
ACTUATOR
- MCU → FINGERPRINTUARTSerial communication for fingerprint enrollment and matching commands
- MCU → POWER_MGMTGPIOMCU controls high-side load switch for fingerprint power gating and monitors charge status
- MCU → ACTUATOR_MOTORPWMPWM and direction control signals for the H-bridge motor driver
- POWER_MGMT → MCUPowerProvides regulated 3.3V power rail to the MCU and peripherals
Bill of materials
| Part number | Type | Component | Manufacturer | Package | Qty | Datasheet | Match |
|---|---|---|---|---|---|---|---|
| MP4-1M-1M-00 | MCU | Nordic Semiconductor nRF52840 Main system controller, BLE 5.x stack for smartphone proximity RSSI tracking, and overall lock state machine management | Artesyn Embedded Power | — | 1 | Matched | |
18 alternatives consideredAI verified | |||||||
| UART Fingerprint Reader | SENSOR | R503 Optical Fingerprint Module Captures and matches fingerprint biometrics for secure local authentication | Waveshare | — | 1 | Matched | |
12 alternatives consideredAI verified | |||||||
| MCP73831 | POWER | TI BQ25100 & TPS22810 & MCP1700 Manages USB-C Li-Ion battery recharging, high-side power gating for fingerprint sensor, and 3.3V system regulation | MICROCHIP | SOT-23-5 / DFN-8 | 1 | Matched | |
26 alternatives consideredAI verified | |||||||
| DRV8837CDSGR | ACTUATOR | DC Gear Motor with H-Bridge Driver (DRV8837) Actuates the lock deadbolt mechanism upon successful authentication | Texas Instruments | WSON-8 | 1 | Matched | |
7 alternatives consideredAI verified | |||||||
Build guide
6-8 hoursAdvanced
1
Procurement & Preparation
- Procure all bill of materials including Nordic Semiconductor nRF52840 (MP4-1M-1M-00), R503 Optical Fingerprint Module, TI BQ25100 & TPS22810 & MCP1700 power management circuit with MCP73831, and DRV8837CDSGR DC Gear Motor driver.
- Prepare the main PCB workstation, ensuring anti-static mat connection, soldering iron temperature calibration to 350°C, and setup of the USB-C programming jig.
2
Hardware Assembly & Wiring
- Solder the Nordic Semiconductor nRF52840 MCU, power management components (MCP73831, BQ25100, TPS22810, MCP1700), and 3.3V regulation components onto the main PCB. Verify VCC_3V3 and GND outputs using a multimeter.
- Wire the R503 Optical Fingerprint Module to the MCU via UART (TX, RX, GND, VCC_GATED). Connect EN_FP and CHG_STAT control lines between the MCU and power management block.
- Integrate the DC Gear Motor and DRV8837 H-bridge driver. Connect MCU PWM signals (IN1, IN2, NSLEEP) to the DRV8837 inputs and wire the motor outputs to the mechanical deadbolt actuator mechanism.
3
Firmware Setup
- Connect the SWD programmer to the nRF52840 MCU and flash the bootloader and BLE 5.x stack firmware supporting smartphone proximity RSSI tracking and state machine management.
- Compile and flash the application firmware implementing R503 fingerprint template matching logic, DRV8837 motor control routines, and power-saving sleep modes utilizing the TPS22810 high-side power gating.
4
Testing & Calibration
- Perform electrical validation by testing USB-C charging via the MCP73831 circuit, checking CHG_STAT signal reporting to the MCU, and verifying regulated 3.3V power rails under load.
- Test biometric authentication by enrolling and matching test fingerprints on the R503 module, ensuring proper EN_FP gating response and secure local authentication handshakes with the MCU.
- Calibrate the mechanical deadbolt actuation by sending PWM commands (IN1, IN2, NSLEEP) to the DRV8837 driver, measuring torque, stroke length, and operational smoothness within the standard US deadbolt housing.
- Conduct end-to-end integration testing including BLE 5.x smartphone proximity RSSI connection range, automatic unlock triggers, and battery-loss fail-safes.
Document
BLE smart lock
A residential indoor BLE smart lock featuring biometric fingerprint authentication and USB-C rechargeable battery, designed as a standard US deadbolt replacement.
Design Overview
| Item | Details |
|---|---|
| Product Type | BLE smart lock |
| Key Functions | Fingerprint unlock, BLE smartphone proximity unlock, USB-C rechargeable battery power |
| Power Source | Li-Ion Battery |
| Connectivity | Bluetooth |
| Size | Standard US deadbolt replacement |
| Environment | indoor |
| Difficulty | Advanced |
| Est. Time | 6-8 hours |
System Architecture
Power Topology: USB-C input (5V) passes through ESD protection and connects to the BQ25100 Li-Ion battery charger IC to charge a single-cell 3.7V Li-Ion battery. The battery output supplies the DC motor driver directly and feeds a low-quiescent-current MCP1700 LDO regulator to generate a stable 3.3V rail for the nRF52840 MCU and sensors. A TPS22810 high-side load switch controlled by an MCU GPIO gates power to the fingerprint sensor to ensure zero standby current during deep sleep.
Module List
| Module ID | Type | Name | Function | Voltage |
|---|---|---|---|---|
| MCU | MCU | Nordic Semiconductor nRF52840 | Main system controller, BLE 5.x stack for smartphone proximity RSSI tracking, and overall lock state machine management | 3.3V |
| FINGERPRINT | SENSOR | R503 Optical Fingerprint Module | Captures and matches fingerprint biometrics for secure local authentication | 3.3V |
| POWER_MGMT | POWER | TI BQ25100 & TPS22810 & MCP1700 | Manages USB-C Li-Ion battery recharging, high-side power gating for fingerprint sensor, and 3.3V system regulation | 3.7V/5V |
| ACTUATOR_MOTOR | ACTUATOR | DC Gear Motor with H-Bridge Driver (DRV8837) | Actuates the lock deadbolt mechanism upon successful authentication | 3.7V |
Key Components
4/4 modules matched to real parts. See the BOM tab for the full component table.
Nordic Semiconductor nRF52840 (MP4-1M-1M-00)
None of the candidates correspond to the MDBT50Q-1M module manufactured by Raytac, which is an nRF52840-based module.
TI BQ25100 & TPS22810 & MCP1700 (MCP73831)
Candidate 1 is the standard MCP73831 advanced linear Li-Ion/Li-Polymer charge management controller, which closely match
Build Summary
- Difficulty: Advanced
- Estimated time: 6-8 hours
- Tools required: SMD soldering station, Hot air rework gun, Multimeter, DC Power Supply, Segger J-Link SWD Programmer, Oscilloscope
See the Build tab for the full step-by-step assembly guide.
Generated by YuanQi AI Design System · Query: Design a BLE smart lock with fingerprint unlock and USB-C charging