Bike speedometer (CB20497E)

This circuit can be powered by a solar cell. The circuit is from a 1991 documentation having a phototransistor as sensor.

Annunciator (CB6792E)
Found in a 90's EDN this circuit can be used as a shield. The transistor is a general-purpose type and the...
555 2-Range Relay Up to 10 Minutes (CB25535E)
This circuit was found in the November 1992 issue of Radio Electronics magazine. The circuit has...
Super regenerative VHF receiver (CB7516E)
This circuit was found in an American documentation from 1977. The circuit can be implemented with modern...