Inovonics PBX Manual

1305 Fair Avenue • Santa Cruz, CA 95060
Tel: [phone] • Fax: [phone]
— — — — — www.inovon.com — — — — —
OPERATING AND MAINTENANCE
INSTRUCTION MANUAL
MODEL “PBX”
TELEPHONE SWITCH
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TABLE OF CONTENTS
Section I - INTRODUCTION ..............................................1
Product Description - Product Features -
Product Applications - Product Specifications
Section II - PBX INSTALLATION .......................................3
Unpacking and Inspection - Mounting -
AC Mains Power - Radio Frequency
Interference (RFI) - Front Panel Indicators -
Rear Panel Connectors and Indicators -
Connecting the PBX - “Priority Channel”
Section III - PBX OPERATION ...........................................7
Calls Outgoing From the PBX - Calls
Incoming to the PBX - Formatting Auto-Dial
Commands - Using Two or More PBX Units -
The Security Password
Section V - CIRCUIT DESCRIPTIONS .............................10
Schematic Diagram Notes - The “PIC”
Microcontroller - PBX Operation for Outgoing
Calls - PBX Operation for Incoming Calls -
20Hz Ringing Supply - DC Power Supplies -
Parts Listing - Mail-Order Component
Suppliers - Schematic Diagrams -
Warranty (inside back cover)
INOVONICS WARRANTY
ITERMS OF SALE: Inovonics products are sold with an un-
derstanding of “full satisfaction”; that is, full credit or refund
will be issued for products sold as new if returned to the point
of purchase within 30 days following shipment, provided that
they are returned complete, and in “as shipped”condition.
II CONDITIONS OF WARRANTY: The following terms apply
unless amended in writing by Inovonics, Inc.
A. The Warranty Registration Card supplied with the product
must be completed and returned to the factory within 10
days of delivery.
B. The Warranty applies only to products sold “as new.” It is
extended only to the original end-user and may not be
transferred or assigned
C. The Warranty does not apply to damage caused by mis-
use, abuse or accident. The Warranty is automatically
voided by unauthorized attempts at repair or modification,
or if the serial identification tag has been removed or al-
tered.
III TERMS OF WARRANTY: Inovonics, Inc. products are war-
ranted to be free from defects in materials and workmanship.
A. Any discrepancies noted within 90 days of the date of de-
livery will be repaired free of charge, or the equipment will
be replaced at the option of Inovonics.
B. Additionally, parts for repairs required between 90 days
and one year from the date of delivery will be supplied free
of charge. Labor for factory installation of such parts will
be billed at Inovonics’prevailing “shop rate.”
IV RETURN OF GOODS FOR FACTORY REPAIR:
A. Equipment will not be accepted for Warranty or other re-
pair without a Return Authorization (RA) number issued by
Inovonics prior to its return. An RA number may be ob-
tained by calling the factory, and should be prominently
marked on the outside of the shipping carton.
B. Equipment must be shipped prepaid to Inovonics. Ship-
ping charges will be reimbursed for valid Warranty claims.
Damage sustained as a result of improper packing for re-
turn to the factory is not covered under terms of the War-
ranty and may occasion additional charges.

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Section I
INTRODUCTION
Product Description
Inovonics’ “PBX” is a telephone switching “mini-system.” It
allows up to seven dial-up devices (modems, fax machines,
alarm boxes, telephone sets, etc.) to share a single central office
telephone line, both for outgoing and for incoming calls. The
PBX delivers central office dial tone to the first modem or other
device which goes off-hook to originate a call. Calls incoming to
the PBX are directed to the selected device with a touch-tone®
access command from the calling party.
Product Features
Features of the Inovonics PBX include:
•Easy installation with standard RJ11 jacks for telco line
and subscriber equipment.
•Two or more PBX units may be daisy-chained to ac-
commodate additional dial-up devices.
•90-volt / 20Hz ringing voltage generated internally.
•Powered by mains-voltage adapter (supplied), or by Un-
interruptible Power Supply (UPS) at user’s option.
Product Applications
The PBX finds primary utility in remote, unattended equip-
ment installations which may be limited to a single central of-
fice phone line. Such installations might include broadcast
transmitter sites, emergency power plants, pumping stations,
radio repeater huts and weather monitoring locations. In short,
any installation of electronic equipment for monitoring, alarm
or dial-up interrogation which requires occasional, intermittent
access to a standard telephone line.

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Product Specifications
Central Office Compatibility: Standard 48-volt, 40mA sub-
scriber loop equipped for touch-tone service. Connection
via RJ11 jack, polarity protection provided.
Subscriber Set Compatibility: Accepts any modem, tel-set,
fax machine, alarm equipment, etc. intended for direct con-
nection with a touch-tone-equipped central office telephone
line. Connections via RJ11 jacks.
Panel Indicators: POWER, C.O. CONNECT, MODEM CON-
NECT on front panel. Rear-panel indicators next to each
jack light when that device goes off-hook.
Power Requirement: 12VAC at 500mA. A “wall-
transformer”power supply is provided. The PBX will also
operate from an external DC source between 15V and 20V.
Size and Weight: 2”H x 6”W x 8”D; 4 lbs. (shipping).

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Section II
PBX INSTALLATION
Unpacking and Inspection
Inspect for possible shipping damage immediately upon receipt
of the equipment. If damage is suspected, notify the carrier at
once, then contact Inovonics.
We recommend that you set-aside the original shipping carton
and packing materials for possible reuse. In the event of return
for Warranty repair, shipping damage sustained as a result of
improper packing may invalidate the Warranty!
IT IS VERY IMPORTANT that you complete and re-
turn the Warranty Registration Card found at the front
of this Manual. Not only does this assure coverage of
the equipment under terms of the Warranty, and pro-
vide some means of trace in the case of lost or stolen
gear, but the user will automatically receive specific
SERVICE OR MODIFICATION INSTRUCTIONS
should they be issued by Inovonics.
Mounting
The Inovonics PBX is packaged in a plastic box with rubber
feet. Though no provision is included for rack-mounting, the
unit may be set atop any convenient rack-mounted chassis, so
long as at least 2U of panel space above the “host” equipment is
left open to access the PBX. Alternatively, the PBX may be lo-
cated next to the telephone company’s “demarc” and fastened
to the wall or mounting board with a couple of small angle
brackets from the hardware store. Short sheet-metal screws
will secure the brackets to the plastic enclosure.
AC Mains Power
The PBX is supplied with a 115-volt, “wall-mounted trans-
former” power supply. The actual power delivered to the PBX
is 12 volts AC at about 500mA. Though the input power to the
PBX is thus defined, we nonetheless recommend that you use
the supplied “wall wart” whenever possible.

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If the PBX is expected to function during a mains power failure,
whatever standby supply is available for the other equipment
can probably operate the PBX as well. If this is a 115-volt AC
mains supply, no special provision is necessary. If, on the other
hand, other equipment at the location draws power from a bat-
tery backup, the PBX may be powered from this as well. Ap-
propriate DC may be fed directly in to the rear-panel connector
labeled POWER (12VAC) without regard to supply polarity.
This DC feed should be pre-regulated to a value between 15VDC
and 20VDC. If, for example, the standby power source is a 24-
volt battery supply, a simple series regulator may be arranged
using a common “3-terminal” voltage regulator integrated
circuit such as the National Semiconductor LM7815CT.
Radio Frequency Interference (RFI)
We have anticipated that the PBX may be installed in the im-
mediate proximity of broadcast transmitters or 2-way radio
equipment. Nevertheless, please practice some care in locating
the unit away from abnormally high RF fields.
Front Panel Indicators
POWER This LED lights only when the proper voltage is
delivered to the PBX. An voltage somewhat below
the required input will cause the indicator to go
out, though the unit may appear to function prop-
erly.
C.O.
CONNECT
This indicator lights whenever the central office
(telco) line is engaged, either for calls outgoing
from, or incoming to, the PBX.
MODEM
CONNECT
This lights when one of the connected devices
(modem, etc.) is active. For an outgoing call, this
LED will light concurrently with the C.O. CON-
NECT indicator as the telco line is seized. When
the PBX answers an incoming call, this LED will
light once the desired device has been selected
with the appropriate touch-tone address, rung-up
and has answered.

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Rear Panel Connectors and Indicators
POWER
(12 VAC)
This “coaxial power” connector mates with the
plug molded onto the end of the “wall wart” power
supply cord. Nominal connector dimensions are
5mm O.D. by 2.5mm I.D. This is a common con-
nector (Radio Shack #274-1568), should one be re-
quired for alternative power accommodations.
(Note particulars at the top of the previous page.)
TEL LINE This US-standard RJ11 jack connects the PBX to
the tip and ring of the central office telephone line.
Use any standard, 4-conductor “modular-to-
modular” telephone set mounting cord, such as
Radio Shack #279-347 (6-foot), #279-374 (12-foot)
or #279-356 (25-foot).
MODEMS
(1 –7)
These seven RJ11 jacks interconnect the PBX with
the various pieces of equipment which will share
the common central office telephone line. The
same “modular-to-modular” cables may be used as
listed above. NOTE: MODEM 7 is designated a
“Priority Channel.” See explanation below.
Each jack has an associated LED to indicate which
piece of equipment is connected to the central of-
fice line.
Connecting the PBX
As hinted in the foregoing description of rear-panel appoint-
ments, the “wall-wart” power supply is plugged into the
POWER (12 VAC) socket. The central office line is connected to
the TEL LINE jack, and modems, etc. are assigned to the seven
MODEM jacks. Nothing could be simpler, could it?
The use of a second PBX to accommodate additional equipment
is covered on Page 8.
“Priority Channel”
The MODEM 7 jack has been designated a “priority channel.”
Whenever the device plugged into this jack goes off-hook:
1) any existing outgoing or incoming connection is unceremoni-
ously “dumped,” 2) the central-office line is restored to an idle
condition with a two-second delay, and 3) MODEM 7 equipment
is connected directly to the line.

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If an incoming call is in progress when the MODEM 7 “priority”
device seizes the line, the priority device may not immediately
receive and recognize dial tone. Modern modems will not
blindly “dial away” into a dead connection, but will hang up
and try the call again. Results may well depend on the commu-
nication protocol of the equipment which originated the inter-
rupted call. Once communication has been broken by the called
modem being disconnected, the originating equipment may
immediately hang up and then attempt to re-establish commu-
nication. You may wish to edit the dialing routine of such gear,
adding a “wait” command to allow the priority device a chance
to seize the line.
MODEM 7, the “priority channel,” should be assigned to equip-
ment with a vital or sensitive function; a fire or water-level
alarm, for instance. Another candidate might be a remote con-
trol system with a paging provision which automatically sum-
mons a technician in an emergency.

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Section III
PBX OPERATION
Calls Outgoing From the PBX
In the idle state of the PBX, the first modem or other equip-
ment to go off-hook will seize the telco line and receive central
office dial tone. Once this connection is made, the equipment
has a direct, “metallic” connection with the central office line
which will be maintained without interruption until the modem
“hangs-up.” The PBX does not have a call-duration “timeout”
provision. The single exception to this rule is an off-hook by
“priority channel” equipment connected to the MODEM 7 jack.
Anything connected to this jack has immediate priority over any
outgoing or incoming call. (See Page 5.)
Calls Incoming to the PBX
Assuming an idle state, an incoming call will be answered by
the PBX on the very first ring. When the PBX goes off-hook, it
does not return a “second dial tone.” It will wait for a valid
touch-tone command for only 10 seconds before hanging up and
releasing the line. During this 10-second “window,” the PBX
will respond to the proper “security password,” followed by a
single-digit “device number” to ring the desired equipment.
The security password is: ∗-5- #(“star,” the number “5”and
the “number symbol” or “pound sign”). This should be fol-
lowed immediately by the number of the device to be rung. For
instance, ∗-5- #- 3would ring the device connected to the
MODEM 3 jack. If the PBX receives an incorrect security pass-
word, or no touch-tone command at all, it will hang up at the
end of the 10 second window.
When it receives the proper “access string,” the PBX applies
ringing voltage to the selected device. The ringing signal con-
forms to the standard established in the halcyon days of the
Bell System: 90 volts AC at 20Hz, one second on, two seconds
off. The PBX will disconnect if the selected device does not an-
swer within ten rings.

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Formatting Auto-Dial Commands
When equipment connected to the PBX is to be called-up and
interrogated automatically from a “home” location, the pro-
grammed dialing command must be formatted to insert the se-
curity password and device address.
Since the PBX has a fixed, 10-second window to receive this in-
formation, it is important to know how soon this window opens
after the last digit of the telephone number is entered. Within
the same exchange this could be almost instantaneous. Since
nearly all telephone exchanges now utilize digital switching
equipment, there is a very short connection delay even on a
coast-to-coast call. Nevertheless, it is worth placing a call to the
PBX from a conventional touch-tone telephone to confirm the
average connection time in seconds.
Most modems which offer programmed dialing are able to insert
additional access codes, area codes and pauses in the dialing
process. Though these usually precede the telephone number to
be dialed, there is no reason why they cannot be placed after the
number. You must consult the specific instructions supplied
with the auto-dialing modem, of course, but many modems ac-
cept commas in the dialing string to initiate one-second pauses
wherever they are inserted. If the connection delay is estab-
lished at one or two seconds, insert two or three commas be-
tween the telephone number and the additional digits. For in-
stance, dialing:
5- 5- 5- 1- 2- 1- 2- ,- ,- ,-∗-5-#- 3
would dial the PBX, pause three seconds while the connection
was completed and the PBX has answered, then forward the se-
curity password and ring device number 3.
The PBX returns “audible ringing” to the calling party as the
selected device is actually rung-up. This acknowledges receipt
of the proper security password and monitors progress of the
connection at the remote site.
Using Two or More PBX Units
One might ventue that a half-dozen dial-up devices could tax
the limit of a single telco line, even when the intermittent na-
ture of equipment usage is taken into account. There may be
instances, however, when additional equipment may safely be
accommodated by using two or more PBX units.