Door Locking Device

This Project was submitted to Parallax by Todd Ulrich

My project is a locking device for our house. We have used it daily for about four years, and it has been very reliable.

The idea is to provide keyless-entry and an additional locking-device that is much more robust than a typical entry door lock.

A linear actuator built from parts on hand does the work. The controller is a BS2 mounted on the board of education. The H-bridge with opto-isolators is from page 166 of the MicroController Cookbook by Matt Gilliand. It is powered by a 12vdc 1500 ma supply.

The linear actuator consists of a 12vdc motor and worm gear assembly originally used for an automobile automatic seat-belt drive, a powder coated C channel, and a piece of square plastic rod drilled to match the drive gear. There are two small plastic shields to activate the attached photo-interrupt switch.

A hardened steel axel slides through a cylindrical sleeve bolted to the wall. The steel axel is attached to the actuators plastic rod by a T-shaped metal end piece that engages a slotted metal cage welded to the steel axel end. This allows the axel to be detached from the plastic rod for manual operation. The actuator can also be easily operated manually by twisting the brown knob atop the drive motor.

There’s a square metal tube with an angled end attached to the door’s bolt lock twist lever and is spring loaded towards the unlock position.

Outside entry is gained using a garage door type keypad remote control, an additional momentary push-button is used for lock only mode. A red and green LED indicates lock status. As the steel axel reverses, the door’s bolt lock is simultaneously pulled open by the spring.



Locking is achieved by the outside momentary push button or the momentary push button built into the receiver inside the house. As the lock is closing it engages the door’s bolt lock lever and closes it simultaneously.