In this interesting circuit from Popular Electronics, the output voltage is the square root of the input voltage. Equivalent operational amplifiers can be tried out.
This is a very simple atomic radiation detector circuit using a Geiger-Muller tube. The circuit was...
With a 120 ohms resistor this circuit can also be used as a shield for 3.3 V output voltages. The...
This is one of the many universal motor controls that the reader can find on this website. The...