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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Phase Shift Oscillator (MSB039B)
In this oscillator a phase shift network formed by C1, C2, C3 and R1, R3, R4 determine the fase...
Triac Inductive Load Interface or Shield (CB4592E)
For inductive loads we have the configuration shown in the figure. Note that the optical coupler...
3-Bit A-D Converter (CB14253E)
This circuit was found in the Linear Applications Handbook by National Semiconductor. It uses...