The difference between this circuit and the previous one is that it uses PNP transistors. The circuit is from Radio Electronics magazine from July 1968. The frequency depends on R1 and C1.
This circuit, found in a 1986 documentation, uses an optical sensor to count pulses and, in its...
Found in General Electric's 1969 documentation, this circuit uses two Foto Darlingtons to control...
The output voltage of this inverter depends on the employed transformer. The circuit is from a 90s...