ELF Monitor (CB21055E)

This circuit monitors extra-low frequency (ELF) fields. We found it in an American documentation from the 90s.

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Telephone dialer (CB9235E)
This circuit was obtained in Radio Electronics from the 90s. The integrated circuit is uncommon...
10 Hour Digital Clock (CB17007E)
This 4-digit digital clock for hours and minutes with CMOS integrated circuits was found in a 1995...
Preamplifier for Microphone (MSB062E)
This circuit is indicated to operation with low intensity sources such as electret microphones and...