This automatic brightness control that uses an LDR as a sensor, was found in American documentation from the 1980s. Resistors in series with LEDs depend on the desired current.
Analyzing the circuit shown in the figure we see that the difference in relation to the others is in...
This simple 15 V power supply was found in an article describing an assembly in the January 1987...
This 1 transistor circuit is from a Radio Electronics from December 1958… The circuit is battery...