Intercom with telephone (CB7829E)

Old phones with dials can be used in a simple home intercom system, as this circuit from Popular Electronics from the 90's shows.

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Wireless microphone (CB9457E)
This version is one of many that can be found on our website. We found it in Radio Electronics from the...
Telephone Monitor in Use LM3909 (CB24688E)
This circuit for common analog telephones was found in March 1982 Radio Electronics magazine. It...
Using the 4510 Up Down Counter (CB180)
Figure bellow shows how the 4510, a divide-by-1U, up/down counter with three-state outputs is...