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How can I use a capacitor to ring a landline phone over and over again. I assume I need to develop such a circuit like below with a cap placed on one of wires. I think the cap would charge, and when decharging, it can ring the landline phone. If such a scheme is possible, does anybody know how I can calculate the needed capacitance for the cap.

schematic

simulate this circuit – Schematic created using CircuitLab

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closed as unclear what you're asking by Matt Young, Enric Blanco, Voltage Spike, Dave Tweed Jun 8 '17 at 21:52

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    \$\begingroup\$ No, that won't work. The ring voltage supplied by the central office is (if I recall correctly) pulses of about 90 Volt 20 Hz AC. There is no simple way to reproduce that with a few passive components. \$\endgroup\$ – Peter Bennett Jun 8 '17 at 4:08
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Putting a capacitor in series with a phone like that will allow it to ring when the "main distribution facitilty" (I'm assuming you mean FXS, central office, or PABX etc) signals a ring but it will not be able to answer or make calls. it will not cause it to ring at other times .

For the capacitor 10uF 100V non-polarised sounds about right.

Some phones may behave strangely in this configuration at they require a DC supply for correct on-hook operation. (eg Alcatel TF200 series)

Now, if you have a phone and want to make it ring you need the 90V AC mentioned in the comments, you can find this on a ringing phone line. or make it using a PABX or FXS adaptor or a ring generator circuit.

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