Telephone dialer (CB9235E)

This circuit was obtained in Radio Electronics from the 90s. The integrated circuit is uncommon today.

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Active Inductor (CB5342E)
This circuit is from an 80's electronic component manual. It has the way to simulate an inductor...
Receiver for Heart Rate Monitor (CB25407E)
This is the receiver for the previous circuit found in the November 1991 Radio Electronics...
Frequency switch (CB8095E)
This circuit was found in a Popular Electronics documentation from the 90s. It is possible to switch...