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who can explain the process of detecting phone ringing?

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a_tek7

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detecting phone ringing

who can explain the process of detecting phone ringing?(with a circuit is better)
 

laktronics

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Re: detecting phone ringing

Hi,
The ring voltage of analog telephone lines is AC voltage of about 70V RMS,and about 50 to 100HZ frequency superimposed on a nominal DC battery voltage of 48V/24V, depending on the systems. The ring circuit therefore should detect the high Voltage, low frequency AC component of the telephone signal, since most of the other AC signals like speech and tones are of sub-volt amplitude and lying in 300 to 4Khz band typically. For call metering purpose, however, signals of 12 to 16KHZ are used.

So, to detect ring voltage, use a set of back to back zener diode of 18V to 27V,1/2W in series with a 1µF, 250V AC nonpolar capacitor, and a 10K to 18K, 1/2W resistor across the telephone line. If you just want to monitor, introduce an LED in series with the above components and connect a reverse connected diode across the LED to protect it. LED will glow when the line rings. If you want a logic level, connect an opto isolator in the place of the LED and take the logic level from its output collector, pulled up to Vcc. Connect a 10µF electrolytic capacitor between the collector and emitter (ground) to get a DC level. Isolator is required generally since +ve of the telephone battery is grounded at the exchange.
Regards,
Laktronics
 

ramesh

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Re: detecting phone ringing

laktronics said:
Hi,
The ring voltage of analog telephone lines is AC voltage of about 70V RMS,and about 50 to 100HZ frequency superimposed on a nominal DC battery voltage of 48V/24V, depending on the systems. The ring circuit therefore should detect the high Voltage, low frequency AC component of the telephone signal, since most of the other AC signals like speech and tones are of sub-volt amplitude and lying in 300 to 4Khz band typically. For call metering purpose, however, signals of 12 to 16KHZ are used.

So, to detect ring voltage, use a set of back to back zener diode of 18V to 27V,1/2W in series with a 1µF, 250V AC nonpolar capacitor, and a 10K to 18K, 1/2W resistor across the telephone line. If you just want to monitor, introduce an LED in series with the above components and connect a reverse connected diode across the LED to protect it. LED will glow when the line rings. If you want a logic level, connect an opto isolator in the place of the LED and take the logic level from its output collector, pulled up to Vcc. Connect a 10µF electrolytic capacitor between the collector and emitter (ground) to get a DC level. Isolator is required generally since +ve of the telephone battery is grounded at the exchange.
Regards,
Laktronics

It is better to explain with a proper circuit diagram for clear understanding.
 

GUGLHUPF

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detecting phone ringing

I second Ramesh. I had almost the same problem the same day (need to detect a 24VAC in a MCU). I tired to completely understand the post but could not :-( A diagram would be best or a more thorough explanation. I know this is asked a lot but would be well appreciated.
 

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