This 1967 Philips circuit recognizes a light signal (visible or infrared) modulated by tone. The circuit makes use of components of the time that are equivalent to the current BCs.
The circuit presented is from the Linear Databook of Motorola of 1990. With it we emulated a NOR gate...
This circuit was obtained in a 1977 magazine, but it can still be assembled with BC548...
This circuit produces sounds that depend on the measured voltage and that can be compared with a...