SP-1
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16
INITIATING SPEAKERPHONE CALLS:
While the MC65118 IC makes provision for adding a DTMF tone dialer, the
simplest and least expensive approach rate an ordinary telephone set as part of
your Speakerphone installation. The average electronics buff is well aware that
suitable phones are abundant at negligible cost, often with memory and other
handy features. Simply connect the auxiliary phone and your SP1 to the phone
line with a commonly-available dual-modular adapter, or use a dual wall jack,
etc. Use the auxiliary phone for dialing, incoming rings and situations where
you prefer a handset. Enjoy the Speakerphone for efficient, hands-free
communication. Be sure to hang up the auxiliary phone after turning on your
SP1 Speakerphone.
RINGER CIRCUITS:
The SP1 does not include a ringer circuit for the simple reason that the average
home, shop or office already has plenty of ringer noises whenever there are
phone calls. If you are a telephone electronics enthusiast and really want a
built-in ringer circuit, it is up to you to understand and comply with telephone
company ringer circuit equivalency requirements.
OPTIMIZING YOUR SPEAKERPHONE SET-UP:
There are three variables to be considered in any line-powered Speakerphone
installation:
1. Positioning of speaker in relation to the microphone.
2. Your distance from the telephone switching complex which supplies line
voltage. (If the voltage is marginal because you are on a distant point of the
phone company "loop," supplementary battery power may be needed for this
or any other Speakerphone.
3. Basic "talk power" of the party on the other end. Let's consider the three
details. First, if your Speakerphone works perfectly from the moment you set
it up, then you are in great shape. Otherwise, consider the following:
A. In general, some degree of acoustical separation must be provided
between microphone and speaker. Put simply, they should not "point" at
each other, or there will be some form of oscillation or erratic operation.
Some experimenting may be needed. See also the section, Understanding
Speakerphone Operation.
B. Usually, telephone line voltage is sufficient for good SP1 performance.
However, the available voltage is determined by the distance of your
location from the central office and local factors. The easiest way to
determine if a supplementary battery is needed is just to try it out. Please
study the section Installing Optional Battery before making any type of
