Smart Padlock

Overview

A smart padlock merges conventional mechanical locking with biometric and wireless control. This unit identifies an authorized user by fingerprint, verifies the match on the Biometric Processing MCU, and if approved, triggers the Solenoid Coil to withdraw the Plunger Rod. The Catch Plate then releases the Stainless Latch Bar, allowing the Motorized Latch to swing open without mechanical key.

All electronics live in a single sealed chamber within the Weatherproof Housing. A Control Board arbitrates between the fingerprint module and the unlock command, runs Bluetooth, manages power, and monitors battery state. The Rechargeable Battery Pack delivers current to the solenoid on demand; a Solenoid Driver FET switches the high inrush. The Weatherproofing Kit keep rain and saltwater away from the electronics. An RGB Status LED signals lock state; a mechanical Override Button allows manual emergency unlock with a stored code.

How it works

The user places their finger on the Capacitive Sensor Array, a capacitive array that detects skin ridge topography. Analog voltages are digitized and sent to the Biometric Processing MCU, which extracts ridge-end minutiae points and compares them against enrolled templates stored in protected flash memory. If the alignment score exceeds the verification threshold, the biometric MCU signals the Main MCU.

The main MCU then energizes the Solenoid Driver, a high-side MOSFET that closes the solenoid circuit. Current rushes through the Solenoid Coil coil (typically 2–3 A at 3.7 V), generating a magnetic field that pulls the Plunger Rod down. The rod retracts, freeing the Catch Plate, and the spring returns it when de-energized.

The entire sequence, sensor read, biometric processing, solenoid pulse, and LED feedback, completes in under one second. The Bluetooth LE Module also listens for unlock commands from a paired smartphone app, allowing remote unlock over Bluetooth (typically within 100 m). The Control Board logs unlock events to flash for audit trails.

Power is stored in the LiPo battery pack, which includes a protection circuit to prevent over-discharge and over-charge. When depleted, the charging port accepts standard micro-USB. A low-battery alert on the RGB Status LED indicates when a charge is due.

The gasket suite, primarily O-rings and a hydrophobic membrane, maintains IP67 rating. O-rings compress at the shell seams; the vent membrane allows pressure equalization but blocks liquid ingress. Silicone sealant is applied to fastener gaps for added weather resilience.