A Maker named Andrea recently constructed a keypad door lock using an Atmel-powered Arduino Uno (ATmega328). As the HackADay crew points out, the entire build is made out of scrap parts: some DVD’s, a bit of wood, an allen key, a motor and belt from a broken printer, an old hard drive (HDD) enclosure and a few power supplies.
“I installed a keypad on my room’s door, and built a simple pulley system to operate the locking mechanism. The final design truly doesn’t look too beautiful because of the major limitations I had to deal with (namely no nails or screws to be used), but it works like a charm,” Andrea explained in a recent blog post. “The big pulley attached to the key-axis is build using DVDs and some scrap wood I had laying around. Such pulley is operated by a DC motor and a belt that I scavenged from my flatmate’s old printer.”
According to Andrea, the case for the electronics is actually an old 3.5 inches hard disk case which conveniently provides nice housing and both 5V and 12V power supply.
“I’ve fit the H-bridge motor driver inside of it, while an homemade I2C keypad driver was fit right behind the keypad, on the outside of the door. A switch is positioned on the inside for easy operation. A timer function is implemented to lock the door after 5 seconds of pressing a button,” he continued.
“A built in speaker serves both as audible output device and (this yet to be implemented) as knocking sensor. The locked/unlocked status of the door lock is stored in EEPROM at every interaction to prevent inconsistencies in case of temporary power loss.”
Meanwhile, the device resets itself every 5 minutes of idle state to prevent possible memory leaks or program halts, with special codes built into the firmware to forcefully unlock the door in case of malfunctioning mechanism (and to modify the pin code). However, Andrea says he isn’t done with the basic design, as it could be improved by installing a sensor to detect the status of the door, along with some form of backup power.
“I am planning to use the existing speaker as a knocking-pattern sensor, as well as adding a door-status LED and infrared remote control. At the moment I have no feedback from my desk regarding the status of the door,” he noted.