In the US, their are PUBLIC and PRIVATE payphones. The private phones use a smart board that has rates information and personality programming for the particular location and customer preferences. It must make all decisions as to answer, type of call allowed, length of call, billing info including call routing as far as whether to send calls to an operator service or let go directly to the phone line as dialed. PUBLIC or "Bell" phones are mostly semi dumb. The computer is in the central office and makes the decisions. The phone is controlled by tones. When money is deposited, tones are sent to the central office based on how many nickels are deposited. A quarter is handled as 5 nickels, etc. The line is controlled for coin relay either collect or return of money by the central office battery voltage and polarity. The phone company here is phasing out PUBLIC payphones because of the proliferation of cellular phones. People no longer want to pay 50 cents to make a call when they can use their own phone in private out of the rain for much less per call. We put smart debit cards in some of our phones, those intended for other countries, that would read the card and add or delete value to the card. It is possible that what you are hearing is the data for writing and reading the card bleeding into the audio circuits of the phone. We used voice prompts in the phones, up to 8 languages, but some customers still wanted LCD messages to the user. We even put cellular phones on trains and buses. Solar powered cellular in Mexico and South America (Brazil). Attila Muhi 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----- > Fren: Larry Williams > Till: PICLIST@MITVMA.MIT.EDU > Datum: den 14 december 2001 07:21 > Dmne: 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