RTS CS9500, User Manual

Page: 67 / 95

DTMF-TO-ROTARY CONVERTER
BOARD
PURPOSE
The DTMF-to-Rotary Dial converter board takes DTMF (dual
tone-multifrequency signals, or
and converts them
into rotary dial (decadic) pulses.
THEORY OF OPERATION
The phone line
is
passed through this board, which has a loop-
current detector and relay. Another relay is used to
the hybrid off the line during pulse dialing.
are
fed from
.
input of the hybrid (send) to a DTMF
chip, which, in drives the pulse dialer IC. A n LED
on the board indicates on-hook, off-hook (OK to dial) and time
out. The pulse dialer chip
is buffered from the relays with
an
open-collector output device. Another signal is taken to the
hybrid's ON pin to
turn the hybrid on during pulse
dialing
and to
hold the hybrid in the mute state. This prevents the "clicks and
of the pulse dialer relay from being audible. The hybrid's
telco line is fed into a phantom talk battery during dialing, to keep
the "Super" Auto-answer line detection circuitry from releasing
the line by
the hybrid off.
There are two independent decoder circuits per card. Some ICs are
shared by the
two
circuits, however.
When the DTMF-to-Rotary converter board is being
used,
the tones
are received from the hybrid send audio. That means that the
send gain trimmer
affects
this
level and the LED meter indicates
it. If the tones are too hot (input meter LED
is
lit during the
presence of tones), the input trimmer must be
turned
down or the
tone level reduced externally. If the tones are being clipped, the
decoder board may not properly recognize the tones.
Special Note Regarding Phone Lines
With the DTMF-to-Rotary converter board installed, the unit
must be connected to a "pulse dial only" line.
If the phone line
can
detect DTMF, the unit will not dial properly, because some of the
ON€ DTMF-TO-ROTARY CONVERTER BOARD