We found this circuit in an old American publication from the 1980s. Transistors can be general-purpose types like the BC548, and the tuning frequency is given by the L and C components.
In the figure we have a sensor circuit that makes use of common transistors and a photo diode as...
This unusual configuration, but which has already been explored in other articles, uses diodes in the...
This circuit uses a modulated signal from a PLL 567 to operate safely with an infrared emitter. The...