Early in my career, I knew a woman who had a medical condition that confined her to an electric wheelchair and made her speech quiet and hard to understand. When she was in a crowd, it was hard for her to navigate through it because people did not see or hear her.
I built her a simple two transistor siren that could be attached to the chair and was operated by pushing a momentary push button. When people heard that siren (it was not loud) they moved out of her path. She was tickled with it.
That was one my first few circuits too. Much before I studied engineering, since my childhood I was passionate about building small electronic gadgets by referring to books/magazines which used to publish hobby circuits. Even though I did not fully understand how that circuit worked, I built that circuit with two transistors and a small speaker form an old radio. My friends and I had fun with that for some time.
Blog Make a Frequency Plan Tom Burke 17 comments When designing a printed circuit board, you should develop a frequency plan, something that can be easily overlooked. A frequency plan should be one of your first steps ...