Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!mailrus!ncar!asuvax!hrc!xroads!wiz
From: wiz@xroads.UUCP (Mike Carter)
Newsgroups: sci.electronics
Subject: Re: Answering Machine Questions
Summary: DAA's and the FCC
Message-ID: <781@xroads.UUCP>
Date: 3 Aug 89 06:10:29 GMT
References: <5337@sybase.sybase.com>
Distribution: usa
Organization: Crossroads, Phoenix, Az
Lines: 47

In article <5337@sybase.sybase.com>, ed@apricot.sybase.com writes:
> 
> 
> I'm building a project which is essentially a microprocessor based phone 
> answering machine.  I have completed all of the basic hardware and firmware
> and am currently using a device that is manufactured by Cermetek (CH1813)
> which provides a DAA for my device.  It also provides ring-detect, off-hook
> detect, audio coupling to the phone line and a means for forcing the line
> off-hook and on-hook using a TTL level signal.  However, this thing is 
> expensive and there are number of other things that I would like to do.
> I don't really have the experience to know how to proceed.  Any tips
> on these things would be appreciated.  Also, any tips that indicate the 
> reasons why any of these things could not be done, or would be expensive to 
> do would be very useful.
> 
First off, let me remind you that there are very FEW companies that make
telephone interefaces that are liscensed. Cermetek is one of them.
A while ago I was contracted by a company in Atlanta GA to make a similiar
device..although its uses slightly different. Registration of your device
with the FCC is important unless you wish to get sued if something happens
down the block to a lineman with 110VAC.
I used the Cermatek CH1810. SLightly cheaper than the 1813.
Detecting rings etc is accomplished by using a bridge rectifier tied accross
the line. The output fed into an op-amp and into a cap. This will provide
a pulse (cap not necessary) each time ringing voltage is applied to the line.
WHat you do with the pulse is up to you. YOu can also observe the
characteristic drop-off when the calling party disconnects. (CPC).
You may not have CPC in your area, most do however.
(It's a quick positive going-pulse out of the bridge).
 
The big issue with part 68 registration is liability and ISOLATION from
device to phone line. If you think for a moment Aunt Granny and Dr Snobby
next door wont complain about the "BUZZING" on the phone line you've got
another thing comming....mostly the dreaded PHONE COPS! (These guys are
really something).
I really advise you to stick with the $26.00 CH1813 . Unless you want to
go through the rigamarole and hassles and $$$$$ to get the device FCC
registered. 
 
Getting flogged by Phone cops brandishing 300 conductor wire isn't fun.
 
-Mike
-- 
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= Mike Carter  N7GYX, Phoenix AZ| Q: Why did the Chicken cross the road  ?  =
= hplabs!hp-sdd!crash!xroads!wiz| A: To ESCape the Main Menu .              =
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