Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!uakari.primate.wisc.edu!aplcen!haven!wam!rustyh From: rustyh@wam.umd.edu (Rusty Haddock) Newsgroups: sci.electronics Subject: Re: Pay Telephone at Home Keywords: Telephone Message-ID: <1990Jul16.232243.8606@wam.umd.edu> Date: 16 Jul 90 23:22:43 GMT References: <1990Jul10.180944.12143@watdragon.waterloo.edu> <1990Jul12.143201.2416@ux1.cso.uiuc.edu> Sender: usenet@wam.umd.edu (USENET Posting) Reply-To: rustyh@wam.umd.edu (Rusty Haddock) Distribution: sci Organization: University of Maryland at College Park Lines: 49 In article <1990Jul12.143201.2416@ux1.cso.uiuc.edu> wehmer@aries.scs.uiuc.edu (James Wehmer) writes: > > My current problem is how to regulate the local calls now that we >must pay for every call. I want a system where the kid must go to some >central location, put a nickle into a box, and all the phones in the >house will be activated for one and only one call. At all other times >I still want to be able to receive incomming calls. This system sounds >a lot like the standard pay telephone at a gas station and we could have >one installed if I can't come up with another option. > How does the circuitry in a pay phone work? How can I sence >when the call is over? How can I still allow incoming calls? I have a >BS. in EE so a complex circuit is no problem and the labor I put in >should pay off in the long run. But this sort of thing has been done >before and I don't want to re-invent the wheel, so I'm asking for >ideas. Thanks in advance! I have a pay-phone at home. I picked it up a ham flea market last year. It is one of the new bread of COCOTs (or Customer Owned Coin Operated Telephone). Unlike the phone company's sets these phones must do all the rate calculation and call completion detection by themselves. A ROM holds the rate information (based on the location of the phone and the number to be called) and a rudimentry FFT is performed on the first few words of the called party's response to determine if the call has been established. My phone was made by a company in Sarasota Florida called ELCOTEL. It has a box made by AT&T (Western Electric) , so it looks exactly like a Bell-Atlantic type pay-phone, but Elcotel made the electronics. If you buy one from them it will cost you alot more than the $100 it cost me! AT&T will also sell you a COCOT. I also saw some of the panel mount phones (like you see in shopping malls) in a surplus store in Pheonix Az called MHZ electronics. (Might be worth a try). regards, Michael. _______________________________________________________________________ Michael Katzmann Broadcast Sports Technology Amateur | vk2bea (Australia) 2135 Espey Ct, Radio | g4nyv (U.K.) Crofton MD. Stations | nv3z (U.S.A.) ...uunet!mimsy!arinc!vk2bea!michael -- Rusty Haddock o {uunet,att,rutgers}!mimsy.umd.edu!fe2o3!rusty Laurel, Maryland o "IBM sucks silicon!" -- PC Banana Jr, "Bloom County"