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 source was found in Philips' 60s documentation. The transistors are from the era and the...
This circuit is the digital indicator for the previous circuit and can be used with similar...
Found in a 90s Electronic Design, this circuit operates with Maxim components of the time. The...