[sci.electronics] modems

robert@uop.UUCP (Robert McCaul--The Equalizer) (07/23/87)

the other day i was musing over something that had me abit
angry a few months back...

even with the prices plummeting, would it be cheaper to build a
modem?

where would i go about getting parts?

i have lots of chip catalogs that list such things as modem chips..

but would it really be worth it?

just curious, as this 300 baud beastie is *real* slow...

i thought a fun project would be to throw a modem together on a
weekend or two...

please send e-mail, i will summarize if there is enough interest.


         "He reads all the time....is that healthy??"

...sun!ptsfa!cogent!uop!robert   
                               ...seismo!lll-crg!ucdavis!uop!robert 

larry@kitty.UUCP (Larry Lippman) (07/23/87)

In article <426@uop.UUCP>, robert@uop.UUCP (Robert McCaul--The Equalizer) writes:
> even with the prices plummeting, would it be cheaper to build a
> modem?

	It might be theoretically cheaper in component cost, but you would
spend a hell of a lot of time doing it.

> where would i go about getting parts?
> i have lots of chip catalogs that list such things as modem chips..

	Assuming that you want an "auto-dial" modem, there is much more to
the modem that the actual modem IC.  You need a DTMF or rotary-pulse dialer,
call progress tone detection, telephone line interface, and logic to handle
commands and do dialing.  This logic is much too complex to perform with
discrete components, so it requires a microprocessor - like an 8051.
	As an example, consider the Silicon Systems SSI-K212 modem IC.
This IC comes out with a microprocessor data bus interface - so it MUST
be used with a microprocessor.  While this IC has a built-in DTMF dialer
and call progress tone detector, it has no telephone line interface, and
still requires a rotary dial pulsing circuit.
	As I see it, writing the microprocessor code to make this IC
work is not a trivial task.  I would guess that you would require at
least 500 lines of 8051 code to emulate a Hayes modem command set.
	
> but would it really be worth it?

	In my opinion, no.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
<>  UUCP:  {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry
<>  VOICE: 716/688-1231        {hplabs|ihnp4|mtune|seismo|utzoo}!/
<>  FAX:   716/741-9635 {G1,G2,G3 modes}    "Have you hugged your cat today?" 

rex@otto.COM (Rex Jolliff) (07/28/87)

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In article <426@uop.UUCP> robert@uop.UUCP writes:
>the other day i was musing over something that had me abit
>angry a few months back...
>
>even with the prices plummeting, would it be cheaper to build a
>modem?
>
>where would i go about getting parts?

If I remember correctly, there was a curcuit cellar article in an issue of BYTE
magazine several months ago that talked about this axact thing.  He didn't
actually discuss the construction of the modem because it was too simple.  The
modem only used one chip! I believe the chip was called 'MOSART' or something
like that.  It did some amazing things according to the article, like detecting
busy/disconnected/ring signals, and even direct control of  A/D and D/A
converters connected to the audio channel(I think). The article made this chip
sound like it had everything but the kitchen sink.

If you wnat the name of the company and you can't find the right mag., let me
know and I'll dig it out of my pile of old bytes.

                                                            Rex
-- 

Rex Jolliff  (rex@otto.UUCP, {akgua,ihnp4,mirror,sdcrdcf}!otto!rex)
The Sun Newspaper -            |Disclaimer:  The opinions and comments in
Nevada's Largest Daily Morning | this article are my own and in no way
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