Sometimes, a circuit grows organically instead of being designed up front and then soldered together. While it's not that great a way to build stuff from an guaranteed-to-always-work point, it's nice to do once in a while. Let me show you by giving an example.
My day job is in a building which used to house multiple companies. In time, however the company I work for has grown such an amount that we now occupy the complete building. I and some collegues, for example, do our work in an office that used to house another small company.
One of the last remnants of the old occupants is the doorbell outside of the office, in the hallway of the building. For some reason, the company that moved away decided it was a good idea to have a doorbell there that rings a chime inside the office. (Not the one in the picture mind you, the office isn't that old.) After we moved in, ofcourse, some of the people I worked with now insist on ringing that bell every time they come in. I don't mind, but I found the continuous 'ding-dong' a bit monotoneous. I decided that April the first would be a nice date to adjust the sound a bit.
So, how to make that old doorbell less boring? By having it make multiple sounds, for example. A bit of electronics with a speaker and some memory to store the samples should do just fine. Unfortunately, I decided to build one just a day before my last chance to install it... so I had to design it around whatever components I had in my component drawer.
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