joe@wateng.UUCP (Joe Morrison) (05/10/85)
I am trying to build a 300 baud direct connect modem around the TMS99532 (from TI) and I need to know how to interface to the telephone lines. I have several articles on *accoustically* coupled modems, but I can't find anything on direct coupled ones. Questions - the jack that plugs into the wall has four coloured wires coming out of it -- what do the four colours mean? What happens when the phone rings? Does the voltage on one of the wires go high or something? How can you tell if the phone is off the hook? Any ideas on how to actually interface the TMS99532 to the phone lines? I'm told I need to use an isolation transformer... Any information on any of the above things would be greatly appreciated! If I get lots of replies that don't conflict with each other (:-), I will post the info to the net. Thanks in advance! - joe -- Joe Morrison, University of Waterloo, Ontario, Canada -- -- -- -- decvax ! -- -- -- -- allegra ! watmath ! wateng ! joe -- -- -- -- -- ihnp4 !
ron@brl-tgr.ARPA (Ron Natalie <ron>) (05/13/85)
> Questions - the jack that plugs into the wall has four coloured wires > coming out of it -- what do the four colours mean? What happens when > the phone rings? Does the voltage on one of the wires go high or something? > How can you tell if the phone is off the hook? Any ideas on how to > actually interface the TMS99532 to the phone lines? I'm told I need > to use an isolation transformer... > Well, it would be safer to use a transformer or a capaciter. Only two lines get used essentially (the center two, if I remember properly). There is about 45 volts across them. The ringing is done by putting 90 volts of low frequency AC on the line (you can make a really nice visual ring indicater with a neon bulb since the thing is designed for that volatage and as very high resistance when it is off). Of course the real problem is that you can not legally just hook up to these wires. The interface has to be approved. This means either getting some kind of DAA or using an approved interface chip. I don't know enough about the chip your using or chips in general to recommend anything. -Ron
tpchmara@wateng.UUCP (Thomas P. Chmara, Creative Slothfulness Inc.) (05/16/85)
One idea that I had some time ago for interfacing to phone lines is to take
advantage of the telephone revolution we've been having lately: buy yourself
a $9.95 (CDN) el cheapo telephone (which is, note, approved) and replace
the microphone and speaker with your own electronic interfaces. This gets
you past the interconnect problem
(This is MY idea! Use it, but don't make any money on it, or I'll
take it back!)
---tpc---
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...!{allegra | decvax | clyde | ihnp4 }!watmath!wateng!tpchmarahenry@utzoo.UUCP (Henry Spencer) (05/17/85)
> One idea that I had some time ago for interfacing to phone lines is to take > advantage of the telephone revolution we've been having lately: buy yourself > a $9.95 (CDN) el cheapo telephone (which is, note, approved) and replace > the microphone and speaker with your own electronic interfaces. This gets > you past the interconnect problem I'm not sure, but I suspect that the Approved el-cheapo telephone becomes unApproved the instant you mess with its insides, however trivially. For example, its Approved status might well depend on the characteristics of the microphone and/or speaker to some degree. If one wants to be 100% Approved with homebrew hardware, the thing to do is to buy an Approved phone-line interface; such things are available, although they're not as cheap as el-cheapo phones, and I believe they confer Approval on equipment that incorporates them. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
lauren@vortex.UUCP (Lauren Weinstein) (05/18/85)
Nope. It doesn't work that way. Most phones are registered AS UNITS and do not contain separately registered access devices. As such, any modifications you make to such a phone will void the FCC registration. Only those service points that are authorized by the Commission to make changes to registered equipment may do so without voiding the registration. Now if the phone contained a separately registered DAA-type circuit, that would be another matter. Most don't. --Lauren--