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 was found in old documentation, but the transistor may be the modern equivalent BC547....
Found in Popular Electronics from the 90s, this circuit mutes a scanner's speaker in the absence of a...
This electromyography monitor is from a 1978 publication on operational amplifiers. The components are...