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.
The circuit shown in the figure can be used to detect the operation of infrared sources whose...
Found in a 90s Hands On Electronics, this small preamp finds applications like microphones and other...
This circuit was found in a 90s Popular Electronics. The frequency is determined by R3 and C1 that...