Phone circuit (CB8709E)

With this circuit, found in a 80s Popular Electronics, it is possible to use two ordinary phones in a basic intercom.

RF probe for VOM (CB10021E)
With this circuit it is possible to measure RF signals with a common multimeter. Signals up to 200...
Code Practice Oscillator (CB4207E)
Also suitable for use as a noisy alarm, this Morse Code or telegraph practice oscillator was found...
Current Monitor Circuit (CB12972E)
We show in the figure how to implement a current monitor circuit using only an operational...