Alpha and Theta waves modulator (CB26155E)

This circuit, which presents a certain danger and should be used with caution, was found in the Electronics Experimenter Handbook magazine.

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High impedance window comparator (CB6091E)
General Electric suggests this circuit in a 1980s documentation. The operational of the time is...
Passage Alarm (CB12894E)
This circuit, from a 1973 publication, locks the relay when the light that falls on the LDR is cut...
FM Tuning Indicator (CB16434E)
This circuit can be adapted to an FM radio or other receiver that does not have a tuning indicator LED....