The high frequncey beep tone you hear is the meter pulse. This is 12kHz or 16kHz depending on the PTT regulation. With a good design you shouldn't hear it. Regards, Jay At 10:31 14/12/01 +0100, you wrote: >The public payphones in Sweden (almost all of them) use a smartcard. There's a display on the phone which shows how many meter pulses you have left on the card. > >Just before the decrement comes, there's a faint high-frequency tone beep in the receiver. I think that the intention is that you should normally not be able to hear that tone. > >I don't know if there's a similar beep on a normal subscribers line, or if it works in the same way abroad. But, maybe, you will get some ideas. > > >Regards > >Attila Muhi - SM4RAN >-----Ursprungligt meddelande----- >Fr=E5n: Larry Williams >Till: PICLIST@MITVMA.MIT.EDU >Datum: den 14 december 2001 07:21 >=C4mne: Re: [PIC] Telephone charge system > > >>Assuming you are making product for the US, having worked in the >>payphone manufacturing and design, I can say that it is simple, yet can >>be frustrating. To detect an answer, a teltone M980 can detect the click >>when the called party answers. However, the M982 and M984 are used for >>precise ring, busy, and intercept tone detection. Current day phone >>switches will give the caller the "This number is busy" message which is >>impossible to detect from a true answer. You could spend a lot of time >>just revising the software for the different rings you will encounter. >>Some switches give a battery reversal on answer and hangup. There are >>so many oddball rings and busy signals from small independent phone >>companies that you will never be able to get 100% accuracy in >>detection. You can get operator screening on the line to prevent >>collect and third party billing to you number. Hook flash for call >>waiting and three way calls CAN be detected. We did it for prison >>phones. For that, we used a dial click detector, the same one used to >>read a rotary dialed number from the far end for collect calls. On >>answer detect, simply put, look for a ring, then after one ring, start >>looking for a pop, when the circuit connects through, then for voice, >>using the M980. If no pop or noise, don't forget to look for second or >>subsequent ring after the apparent answer. Timing of rings, normally >>2sec on 4 sec off, BUT, non standard rings CAN, and sometimes ARE, a >>little off on timing. >>A truly accurate answer detect circuit would be worth a fortune to the >>developer. Even the ultra modern cellular companies use call duration to >>start the call billing. Some long distance companies do the same >>because answer detect for the destination phone company may not be >>transferred to the company where the call originated. >>GOOD LUCK! >>Dipperstein, Michael wrote: >>> >>> > From: XARA Telecomunicaciones [mailto:xara@velocom.com.ar] >>> > >>> > Hi, >>> > I'm developing a PIC based telephony rate system >>> > I need to identify when the called party pickup the phone >>> > any Ideas? >>> >>> I think you might have a little trouble here. Generally, there is no signaling >>> to the calling party that the called party has answered the phone (unless you >>> count "hello"). >>> >>> There are all kinds of call progress signals that indicate that the called party >>> has not answered the call, and maybe you can use their absence as an indication >>> of an answer. Unfortunately, most of those signals are in the audio band, and >>> probably need to be analyzed in the frequency domain (maybe with a= dsPIC). >>> >>> Just off the top of my head, the following signals mean that the call was not >>> answered: >>> - Calling party hangs up >>> - Ringback (ringing caller hears) >>> - Busy >>> - Fast busy >>> - Intercept (tones followed by message) >>> >>> There are also some nasty scenarios that you need to be able to handle to get a >>> good count: >>> >>> 1. Conference calling (three-way calling). Here someone can call you, and you >>> can call someone else without ever hanging up. You will be billed for= the >>> outgoing call. >>> >>> 2. Call someone, then receive a call on call waiting. Switch to the other call, >>> and some time later the person on the first call hangs up. You will only be >>> billed for the time the first person stayed on the line. >>> >>> 3. Receive a call with reversed charges. You will be billed, but didn't make a >>> call. >>> >>> 4. Receive an automatic call back when a busy number that you were trying to >>> reach became unbusy. I think you get charged for the call back. >>> >>> I'm sure that I left several conditions out. I know that in the good old days >>> people made equipment that did what you're trying to do, but I don't know if I'm >>> over looking something, or the network has become more complicated since those >>> days. >>> >>> -Mike >>> >>> -- >>> http://www.piclist.com hint: PICList Posts must start with ONE topic: >>> [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads >> >>-- >>http://www.piclist.com hint: The list server can filter out subtopics >>(like ads or off topics) for you. See http://www.piclist.com/#topics >> >> >> > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics > > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics