RTS CS9500, User Manual

Page: 72 / 95

BASIC AUTO-ANSWER BOARD
Purpose
The auto-answer board is used when automatic answering and hang-up of
the Telos One hybrid
is
desired. The circuit
turns
the hybrid on in response
to ringing voltage on the phone line, and turns the hybrid off
when a break in loop current is detected. The loop current interruption, often
referred to
as
CPC, or Calling Party Control,
is
present on most telephone
lines. However, some central office equipment or may not provide it
and other detection methods will have to be used in that
case.
I n s t a l l a t i o n
The board is installed by plugging
it
into the header connectors on the Telos
One board. Remove the small jumper plugs on H D R l first.
The auto-answer board should be removed and the jumpers replaced if use
with other than Central Ofice-type lines with talk is expected,
since the diodes in the loop detect section will cause severe audio
distortion
if
not biased by talk
Operation
Not much excitement here. With the board installed, the hybrid will
automatically answer and hang-up.
Circuit Description
R4, and form the ring detect section. C2 blocks so that only the
AC ring voltage will trigger When Ul's diode gets current, its transistor
pulls low turning the hybrid on. C3 prevents false tripping.
The remaining components form the loop current detector. When loop
current is present, transistor conducts
and
is discharged. When loop
current goes away, charges through the diode
in
U3 thus causing a low at
for the length
of
the time constant. Upon restoration of loop
current, the capacitor discharges through and The time
ONE ONE BASIC AUTO ANSWER BOARD