Lie Detector (T1534E)

This circuit was found in a Popular Electronics from December 1956. Power is provided by batteries.

Adjustable High Q Notch Filter (CB15815E)
We can implement this filter with more modern equivalent operational amplifiers, since the LM110 is...
LM3914 Overrange Indicator (CB24657E)
This circuit is from an October 1980 Radio Electronics magazine. The circuit indicates when the...
CMOS Two-Tone Siren (CB18974E)
This circuit can be used as a shield when its supply is 5 V. in this case we can exchange the...