zielke@eniac.seas.upenn.edu (Stephen Zielke) (07/07/88)
I am doing a mini-project for an electronics class and I need a little help. I will be building a gadget that will be connected to a phone jack and when it is called it will answer the phone after a pre-set number of rings. After it answers the phone an audio tone will be sent to indicate that it is ready to accept touch-tone commands. The caller can then enter touch- tone commands and a microcontroller will act on these commands. 1. I need a ringing detector. The Texas Inst. TCM1520A will output a TTL level signal during the presence of the AC ringing signal. This would be used to detect/count the number of rings. Anyone ever use this IC or know of a substitute? 2. Answering the phone would be done by closing/opening a relay. Should be no problem here. 3. Sending the audio tone to the caller should not be much of a problem either. 4. Dectecting the DTMF touch tone signals is the main problem. There are plenty of DTMF encoders that are used in the telephone (accepting signals from a keypad). But the DTMF DECODER, which would be present in the central office, seems to be more difficult to find. Anyone know where to get one of these chips? Thanks in advance, Steve Zielke zielke@eniac.seas.upenn.edu ..!rutgers!eniac.seas.upenn.edu!zielke
rogoff@itsgw.RPI.EDU (David H. Rogoff) (07/08/88)
In article <5317@super.upenn.edu> zielke@eniac.seas.upenn.edu (Stephen Zielke) writes: > signals from a keypad). But the DTMF DECODER, which would be present > in the central office, seems to be more difficult to find. Anyone know > where to get one of these chips? > Radio Shack sells a chip that does exactly this. I haven't tried it, but I'd be interested in hearing how well it works. -- David Rogoff, Rensselaer Polytechnic Institute, Troy NY, 518-276-8536 rogoff@itsgw.rpi.edu userea7p@mts.rpi.edu David_Rogoff@rpitsmts (bitnet)
denbeste@bgsuvax.UUCP (William C. DenBesten) (07/08/88)
From article <5317@super.upenn.edu>, by zielke@eniac.seas.upenn.edu (Stephen Zielke): > 4. Dectecting the DTMF touch tone signals is the main problem. There are > plenty of DTMF encoders that are used in the telephone (accepting > signals from a keypad). But the DTMF DECODER, which would be present > in the central office, seems to be more difficult to find. Anyone know > where to get one of these chips? my (uugh) Radio Shack catalog lists oen for $12.95. Its RS part number is 276-1303. It can be found on the top of page 143 of the 1988 catalog. -- William C. DenBesten denbeste@bgsu.edu
johnl@n3dmc.UU.NET (John Limpert) (07/08/88)
In article <5317@super.upenn.edu> zielke@eniac.seas.upenn.edu (Stephen Zielke) writes: >4. Dectecting the DTMF touch tone signals is the main problem. There are > plenty of DTMF encoders that are used in the telephone (accepting > signals from a keypad). But the DTMF DECODER, which would be present > in the central office, seems to be more difficult to find. Anyone know > where to get one of these chips? This month's QST magazine has a couple of ads for DTMF decoders. They are small PC boards with 3-4 chips. Both boards appear to have a LSI decoder chip. If you don't want the whole PC board, you might be able to talk them into selling the chip by itself. Whatever you do, avoid designing/building a decoder that uses the NE567 chip. I have seen alot of these that were ripped out and replaced with a single chip decoder design after the builder got tired of tweaking the decoder circuits every month. Nothing wrong with the NE567, it's just the wrong chip for this application. NET-KALL NK-1 (34.95 KIT 44.95 ASSEMBLED/TESTED) MoTron Electronics 695 W. 21st Ave. Eugene, OR 97405 1-800-338-9058 or 503-687-2118 TD-16 (44.95 KIT) NorCon Engineering P.O. Box 1607 Mooresville, NC 28115 704-664-7817 -- John A. Limpert UUCP: johnl@n3dmc.UUCP, johnl@n3dmc.UU.NET, uunet!n3dmc!johnl PACKET: n3dmc@n3dmc.ampr.org n3dmc@wa3pxx
lharris@gpu.utcs.toronto.edu (Leonard Harris) (07/13/88)
Check out National's telecom databook - I* know I saw one of these in it but I don't have one handy to find the part number. /leonard
gene@cooper.cooper.EDU (Gene (the Spook) ) (07/14/88)
in article <5317@super.upenn.edu>, zielke@eniac.seas.upenn.edu (Stephen Zielke) says: > > 4. Dectecting the DTMF touch tone signals is the main problem. There are > plenty of DTMF encoders that are used in the telephone (accepting > signals from a keypad). But the DTMF DECODER, which would be present > in the central office, seems to be more difficult to find. Anyone know > where to get one of these chips? Sure. Radio Shark used to carry (maybe they still do) a DTMF decoder chip for a few bucks. If you can get your hands on one of them, fine. What I've used before and enjoyed playing with is a neat chip from Mitel (Boca Raton, FL). They have quite a few versions. For example, one is strictly a DTMF decoder, another has both an encoder and decoder on-chip, and both are easily microprocessor interfaceable, to coin a word. Give Mitel a call. If you're nice, they'll be happy to send you a data book, and MAYBE even a sample of the part you're interested in. By the way, the number of the chip I've used is an MM8870, I think. Talk with someone in sales, and they'll steer you in the right direction. As Confucius say, Good Ruck! Spookfully yours, Gene "Rock is my religion; Judas is my Priest."
brian@cbw1.UUCP (Brian Cuthie) (07/14/88)
If you're looking for a good ring detector, the best one I've seen is the Texas Instruments TCM1520A. As far as DTMF decoders go, there are a variety of things to be interested in when searching for one. If you are going to supply local dial tone then you need one with a good dial tone reject feature (like the Teltone M957). If you just want one that is cheap, then the SSI 202P is not a bad choice. Hope this helps. -brian -- Brian D. Cuthie uunet!umbc3!cbw1!brian Columbia, MD brian@umbc3.umd.edu "Captain, Captain! All the stars have gone out!" "No, you fool, you've leaned on the button. Turn the viewer back on!"