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ringing detection circuit

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Hi all..

I have a problem here.
i tried to build a ringing detection circuit.
But when i connect the ring and tip of the telephone cable to this circuit,i found out that it automatically being off hook.
As a result,it cant be used to detect the ringing signal and it get engaged when i call to the telephone.
Is there anyone who can explain to me why it get off hook even there are no ringing signal?
Thanks in advance

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The telephone ringing signal in North America is 90VAC. Your zener diodes are only 3.3V and the 330 ohm resistor creates a huge current with a peak of 370mA. I am amazed that your opto-isolator didn't burn out.

Look at all the ringing detector circuits in Google that use 15V zener diodes and a 10k resistor like this one from a modem:

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Hi guru

Nearly every LED has a max reverse voltage rating of only 5V.

It is a good point for me to put in my memory. But there remains a question: whether such a diode (4148) can bears this 127v ?

Hi  mvs sarma
we can also use a DIAC (conducts  at  32 volts in each diection)

This point is excellent and wonderful, thank you
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