This circuit indicates when the voltage of a 12 V battery is low. With changes, for example, the zener, the circuit can be used to monitor other voltages.
This logarithmic operational amplifier was found in the September 1994 issue of Electronics Now...
Indicated as a joke or challenge this circuit shows how it is possible to control two lamps using...
Found in a Linear Technology 80s integrated circuit manual this circuit has its gain controlled from...