Coin battery audio oscillator
Oscillators, you've been using them all along. This section will give you a lot more circuit ideas and help you understand this very important circuit function.
This project is a simple audio pulse oscillator which is powered by a coin battery as described in project The Coin battery in Electric power.
The 0.01 uF provides a high amount of feedback to sustain oscillations, and the 470K Resistor is used to turn the Transistor ON enough to allow the Transistor to operate as an amplifier (and therefore also an oscillator).
The 100uF Capacitor bypasses the audio oscillator current so that oscillations can be obtained even though the coin battery has a high internal resistance. If the oscillations sound chirpy or die out as you close the Key, the coin battery current output is weak.
Try different materials for the coin battery and electrolyte. You can even try the following with a penny, damp paper and a nickel!!!
How about that for a 6-cent battery that is still worth 6 cents when you are finished with it?!