I set out to solve the problem of wanting to close a door even if you’re not near it. This is useful if you are in bed and realize that your bedroom door is open, or if you are teaching a class and want to keep the door open as students enter but want to close the door when the bell rings.  This could also be useful for the elderly and disabled.

The string is connected to the door and goes through the pulley system. These pulleys change the direction of the string so that it goes directly down the doorframe. Halfway down the doorframe is the locking mechanism that holds the string in place, preventing any movement. Then at the bottom is the weight. The locking mechanism consists of a 3D printed holder and a regular hinge. This locking mechanism catches knots in the string as it goes past the hinge. If the string is going up (as in the door is being opened), the door is not affected. But if you want to keep the door open, the knots engage with the hinge, preventing closing.

An Arduino microcontroller is used to connect a remote control to a servo motor, which is in turn attached to the hinge.  If you are somewhere in the room and want to close the door, you can push a button on the remote and the servo will pull the hinge open, allowing the weight to close the door. This allow for hands-off control.