Busy Line Indicator (CB18711E)

This busy line indicator is very simple, serving for analog lines. The supply is made by two batteries and the transistors admit equivalents.

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Divider by N with the 4017 (2) (CB12131E)
With this circuit it is possible to divide the frequency of a rectangular signal by values between 2...
FM Noise Filter (CB19285E)
This circuit, which we find in a documentation from the 70s, filters out the Ru [occurring in...
Phone Bell (CB18151E)
This circuit simulates the call tone of a telephone. The transducer is a high impedance capsule, and...