Password Door Lock with Solenoid | SimpleCircuits SimpleCircuits Arduino Solenoid Security Security & Access Control Password Door Lock with Solenoid A real, relay-controlled solenoid door lock using Arduino UNO, 4×4 keypad, I²C LCD, and a 7.4V Li-ion + MT3608 boost converter. Three-attempt lockout, auto-relock, animated LCD feedback. 4×4 Keypad 12V Solenoid 3 Max Attempts 10s Auto-Relock 10s Lockout Finished Build 🔒 System Overview How the System Works The user enters a password on the keypad. Arduino compares it against the stored password using the Password library. On match, the relay de-energises to release the ...