I always love building new things and hope to share them all here one day. These projects cost me my discretionary income. Please consider donating and helping me pursue greater and bigger projects. I love you all!
Instead of having a door knob you can instead use a button with a handle and an off switch on the inside to restrict access. Why not? I made this out of a solenoid I had laying around since I was thirteen. The solenoid (while in the door) stays normally in the locked position. It came with a ring around the slug (something I haven’t seen on any other solenoids) so I stretched a spring around it to keep the slug extended until current is run through the solenoid and pulls it shut.
I sketched up the schematic in the first photo above and put it together using all scrap components I had in my parts drawers; all of which are clearly described in the schematic courtesy of my younger self. I carved out my door to accomodate the solenoid and made a strike plate out of hardboard to control the reach of the slug.
There’s a momentary switch for activating the solenoid on each side of the door and a handle for leverage opening and closing. A rocker switch kills power to the relay and “locks” the door. The door turned out to be a lot of fun to use and did the job just great. It has no serious advantage over a normal doorknob other than the enjoyment of using it and the $13 savings.