This circuit was found in a Popular Electronics from the 90s. The transistors are general purpose, and the gain depends on the ratio between R2 and R1.
When a pulse of light reaches the sensor [a CDs cell or LDR] the flip-flop changes its state....
This circuit is an impedance adapter. The circuit is from a Radio Electronics from April 1966. The...
This circuit was obtained in an old American documentation serving only for general purpose NPN...