Telephone Ring Interval detect

[JKJoy]

Hello,

I am designing a circuit to detect telephone ring, to output a flashing light with 2flash/second as long as the other end goes ON-hook. So the flash works for 4-6 seconds in the ring interval(gap between each ring) also, since I dont know if there is next ring coming. I use PIC microcontroller for delay and control. It works fine.
But I feel it awkward to flash 4-6 seconds, even after the other end is gone off-hook.

So my question is, if there any signal change in the phone line which I can detect to stop flashing the very moment the other end phone goes ON-Hook, during ring silence time.


Thanks.

 

[crutschow]

..............................
So my question is, if there any signal change in the phone line which I can detect to stop flashing the very moment the other end phone goes ON-Hook, during ring silence time...................

I don't think so. I believe the blank time between rings has the same voltage as when there is no ring.

 

[Audioguru]

The central office sends you a pulse when the other end goes on-hook. If you call a machine, then the machine can sense that you have ended the call and the machine can also hang up.
But I can't remember if the pulse goes high or it goes low. I think it goes low.

 

[JKJoy]

I believe the blank time between rings has the same voltage as when there is no ring.

That is right. The blank time voltage between rings is the same as when there is no ring.
So that means I cannot achieve what I am looking for.
But is there any current change/loop break which I can sense as part of exchange stopping the ring signal?

Thanks.

 

[Allen6502]

I think this would depend on the type of system used in your country.

In my country ( I used to work in an Ericsson AXE10 telephone exchange), in the older days, we have to install circuits for public phones lines. When the coinbox (Public Phone) was making an outgoing call, and when the called party answered the call, a polarity reversal was sent to the calling party to initiate the first coin to drop into the bank. And following the sub-sequence time intervals, 16 KHz tones were sent to the coinbox for the following coins to drop.

Nowadays, the public phones are so smart. The phone can take care of its charging using a large charging table inside an eprom inside the phone. Some used cradit card size phone cards where coins are not needed.

So to answer your question. I dont think there is any line signals to inform the calling party that the called party has answered the call. There are internal signals inside the Exchange if the call is intra-office. And inter-exchange signals if the call is inter-office. Those signals are either software signals or CCS#7 or MFC signalling.

Allen

 

[JKJoy]

The central office sends you a pulse when the other end goes on-hook. If you call a machine, then the machine can sense that you have ended the call and the machine can also hang up.
But I can't remember if the pulse goes high or it goes low. I think it goes low.

That is really interesting to know there is such a pulse signalling from CO, as the other end goes on-hook.
Can you please explain it little further, whether it is country specific OR is it an international standard?
What about the voltage and time characteristics of that pulse?

Thanks

 

[Audioguru]

I am talking about the North American telephone system since I am in Canada. I do not know what happens in other parts of the world. Some countries have odd standards.
The 50V battery is put on the line during ringing and during pauses between ringing then I think the line goes to 0V or the polarity is reversed for a few hundred ms when the other end answers the call or hangs up.

 

[JKJoy]

I suppose the talk got little confused.
Anyway I am explaining my situation with the picture attached
As you can see Tel-2 end only listen to the ring always, and if there is a ring it will flash the LED until the other end (Tel-1) cut the call. It works well. But I cannot predict in the ring interval period (around 5 seconds), whether next ring will come or not, so I am flashing the LED for next 5 seconds, after the ring has stopped.

My intention is to stop flashing the LED, the very moment Tel-1 has stopped dialing (Tel-1 goes on-hook). I can do it in the ringing duration, but cannot in the interval period between rings.

Thanks