This circuit was found in a 1992 publication. What it does is to light an external lamp when it gets dark. The trigger point adjustment is made in a potentiometer or trimpot and the sensor is a common LDR.
This circuit is from a 1978 publication, and the integrated diode bridge can be replaced by...
The operational amplifier used in this configuration is uncommon today, but more modern types can...
This circuit was found in an American publication from the 60's. The transistor is made of...