Once for kicks I made a 555 oscillator out of discrete parts. I was looking at the internal circuit diagram one day and realized I had all the parts handy: htt

Once for kicks I made a 555 oscillator out of discrete parts. I was looking at the internal circuit diagram one day and realized I had all the parts handy: https://en.wikipedia.org/wiki/555_timer_IC https://en.wikipedia.org/wiki/555_timer_IC You make 1/3 and 2/3 voltage references with three equal resistors in series as a voltage divider and feed those into a pair of op amps that have their other inputs ganged together, the outputs of the op amps go to a flip-flop made of transistors (a 1-bit memory), which controls the filling/emptying of a capacitor (external to the IC) that sets the other (ganged) input to the op amps. The Exploratorium had a physical pneumatic oscillator that worked in a very similar way. A knob on a sliding rod would trip switches at either end of its slide that toggled the left-or-right sliding of the bar by altering the path of the air (from a compressor under the table.)