This is an improved version of the previous circuit also found in the December 1990 Radio Electronics magazine. The duty cycle is also 50%.
The sensor in this circuit is a common transistor like the BC548. The circuit is from a 1979...
With this circuit it is possible to control a relay up to 100 mA with an extremely low input...
Found in an Electronic Design of 1964, this circuit is intended to the signal amplification in the 88 to 108...