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From: Roger Johansson
Subject: Re: Telephone Ring Suppressor
Date: Mon, 23 Sep 2002 11:01:04 +0200
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firstname.lastname@example.org (Nico Coesel) wrote:
>>If your real number is 243512 you just tell all your friends that
>>you've got a new number, 243512-34, and you will only get calls from
>>the people who know this in the future.
>>Others will never reach you.
>>A microcontroller could take the call, listen for the extra numbers
>>tone codes, and hang up or alert the owner with some nice sound or
>That won't work (at least over here). The Public telecom system will
>ignore the extra numbers.
The extra numbers are not for the public telecom system, it is for the
microcontroller which takes the call.
After the phone line has been opened the extra numbers can be heard as
dtmf tone signals, and the uC can identify the numbers and either hang
up again or (if they are the right numbers) alert the owner with a
signal, a sound in a loudspeaker for example.
The person who called will not hear ring signals as usual, because the
device takes the call after the first signal, so the caller will hear
silence on an open phone line while he waits for the owner to pick up
>So, you'll have to make a device that
>answers the telephone,
Yes, and then it listens to what comes down the line next. If they are
the numbers you want it gives a signal to the owner that a call from
his friends is coming in.
>tells the caller to enter the password and wait
>for the digits.
Why tell the caller anything? Your friends already know that they have
to wait for the device to open the line and then they push the two
(If the device is fast enough there may not be any need for a pause.)
>This is a real pain with ISDN or digital PABX systems. In many cases
>these telephones need to be put in DTMF mode by holding a certain key.
As far as I know you can hear when somebody pushes extra buttons
during a call, that sound is what we can use.
But you might be right, and then this solution will not work.
>Not every user knows that.
>Where I'm aiming at is that whenever someone needs you for an
>emergency (say your kid has had an accident in school) that person may
>not reach you because of a device blocking incoming calls.
Okay, but then you cannot have a private telephone, you need to be
available to lots of people in the world, and you will have to accept
all kinds of phone spam.
(to have children is full time job, day and night, so I am happy I
don't have any :-)
I am talking about people who really want to get rid of all calls
except the private calls from close friends.
But it doesn't matter for the construction, it will be roughly the
same except for the details. We still need a device which can take the
call and which can decode dtmf signals. If we also want a voice to
tell the caller something it is an addon part to the basic device.
A programmed ROM with the voice is being played, for example.
>If you really want to get rid of telemarketeers: don't list your phone
>number and only give it to people who need to know your number.
It is not possible to change a number without costs and trouble, not
here in Sweden anyway.
And just not listing your old number would not be very effective, it
is already listed in last years telephone book and telemarketers might
use the last known number.
Or they use number series which they know have many owners, so they
will find you even if your number is not listed.
I have heard that they do that, they just call every number in the
series which is used in that local part of the net.
Where I live we have phone numbers like this 25034, the first three
numbers are a sub-area code, and most numbers below it are occupied,
so they just have to try every number from 00-99 to get every person
in this village.
I ran a bbs 1991-96 and I bought a device which can take a call, tell
the calling person to say something or else the call goes to the modem
instead of to the telephone. That device is something like what would
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