This circuit provides a reference voltage of 2.5 V adjusted in the trimpot. The transistor can be the BC558 (in the drawing it came out as NPN). The control is done by a rectangular input signal.
This receiver for listening to headphones and 2-battery power was found in Japanese documentation from the...
This circuit was found in a Texas Instruments optoelectronics manual and can work with any...
This circuit activates a relay when raindrops fall on the sensor. The circuit is from 1960...