Doorbell

Redid a project from my childhood, which didn't work too well.

Unfortunately, this one didn't either, but it did sorta work.

Basic idea is to make a primitive "oscillator" with an electromagnet: make and break contact using the armature as a switch. Cannibalized the primary windings of an old 12V power supply transform for the electromagnet, and had Shashank do the winding. Turned out to be the only thing he ended up doing, even though this (and the Gauss rifle) were projects I undertook to have him do things other than to play video games. Sigh.

A piece of hardboard ("masonite" in this country, I believe) served as a mounting board for the project. I started out with the idea of making contact posts with little screws and two nuts on top, but ended up not doing that -- the circuit is too simple.

Used the steel reinforcing strip from an old windshield wiper as the armature. Thought that was a master-stroke of ingenuity, but it turned out to be devilishly tricky to make good contact to it, and to achieve just the right flexibility.

Couldn't find a bell (this was a problem in my childhood version, too), so it ended up buzzing anemically, and then only after much coaxing and aluminum foil. Nice L dI/dt sparks, though!