Active with the output at the high level, this oscillator was found in November 1984 Radio Electronics magazine. The supply can be between 3 and 12 V and the output signal is rectangular.
This circuit was found in the October 1983 Radio Electronics issue. It is applicable to old analog...
When the voltage exceeds the value given by the zener, this circuit from a 1990 documentation...
This method of controlling the sensitivity of a phototransistor was found in an Electronics Now from the...