This 80's circuit has been winning. It is a 1 000 gain sample and hold circuit and an offset current setting. The configuration can be adapted to operate with modern equivalent components.
The gain of this circuit depends on the frequency of the input signal. The circuit is from a Radio...
This sensor triggers an oscillator emitting sound when a magnet is approached by a reed switch....
This circuit is from an August 1984 Radio Electronics magazine. It monitors the state of a RAM...