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Stealth
Telephone Screener
Almost
everyone has been annoyed at one time or another by an automated
telemarketing call in the middle of dinner, to find only silence
at the other end of the line. The Stealth Telephone Screener—based
on the PIC16F872—answers the phone and determines whether or
not the caller is an actual person. If not, it hangs up without
disturbing you. Unlike similar commercial products, the caller
does not have to know any special code, and is not even aware
that they are being screened.
The
screener plugs into an ordinary phone line, and has a built-in
ringer to alert you when the caller is a person. It works by
answering the phone, playing a brief greeting (e.g., “Hello”),
and then waiting for a response. If there is no sound for 5
s, or if there is a continuous response that lasts longer than
10 s, then it hangs up. Otherwise, it plays a second greeting
(e.g., “Just a minute”), and activates the ringer, while playing
a ringing signal to the caller. When you pick up any phone on
the same line, the screener stops ringing and releases the line.
The ringers on all of the phones are normally kept off, so you
would never be aware of a machine-originated call when it comes
in.
This
technique eliminates both the “predictive dialing” systems (which
place multiple calls and only connect to the first person to
answer their phone, typically after a delay of more than 5 s,
while hanging up on all other calls) as well as automated systems
that play a recorded message.
Richard
Wotiz, U.S.
dick601@mystics.org
Abstract
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