OHM TECHNOLOGIEES

EPABX DEMONSTRATOR TRAINER SYSTEM

MODEL: EPABX 01

OBJECTIVE:

Ω TO STUDY THE WORKING PRINICIPLE OF EPABX

Ω TO STUDY THE DTMF CIRCUIT

Ω TO STUDY THE CROSS POINT SWITCHING

Ω TO CONTROL AND OPERATE THE EPABX TRAINER KIT

Ω TO LEARN THE PRINCIPLE, MAINTENANCE, TROUBLESHOOTING, AND REPAIR OF A TELEPHONE SWITCHING SYSTEM

MATERIALS REQUIRED:

Ω OHM EPABX DEMONSTRATOR TRAINER SYSTEM

Ω TELEPHONE INSTRUMENTS

Ω C.R.O.

Ω D.M.M.

Ω MAIN SUBSCRIBER’S TELEPHONE LINE

INTRODUCTION:

THEORY:

The EPABX is an acronym of Electronic Private Automatic Branch Exchange. An EPABX has three main components (1) the analog system and analog to digital converter which is basically the various line cards and (2) the cross connection matrix which connects one call to another and (3) the control of the whole EPABX.The EPABX stand for Electronic Private Automatic Branch Exchange. Which means it is an electronic exchange which is privately owned and automatic. It is also known as PBX and PABX.The first part (1) deals with the analog system i.e. your voice coming on two wires and the associated signaling. It converts the signaling as well the voice into digital and handovers

to the matrix. The matrix checks for which port (the no. you dial is just a port of it) is the call meant for and digitally connects the respective port to the calling port. The call is established and held as long as you keep the receiver off hook. The third part maintains the normal functioning of the EPABX including power supply, configuration, troubleshooting and generation of various reports.

In this EPABX trainer kit, we demonstrate the 4 line telephone systems with full signaling and switching functions similar to those of the central office systems. Dial tone, busy tone, and ring tone are provided during call progress. Ringing is generated at the receiving end of the phone being called. Switching employs integrated circuit (IC) matrix switches on four buses. Thus, this system is expandable to 8 lines (4 pairs) if more hardware is added. This system is switching on the Dual Tone Multi Frequency (DTMF) dialing signal and does not work with pulse dialing signal founded in some older phones.

High level design The telephone systems we built consist of the phone line interface circuits and the MCU on the STK500 development board. Each phone line interface circuit has the following hardware.

• Ringer

• Hook switch relay

• Tone frequency generator

• DTMF receiver

• IC switch

The four phones share a common ringer; for all the other components, each phone has its own individual. This is primarily due to the wattage rating of the ICs, we use. The MCU on the STK500 is the central brain of the systems, whose embedded software provides the control functions to each of the phone line interface circuits connected to it. PORT-A is used as the address bus, which, via decoding logic, provides the enabling signal to appropriate functional units. PORT-C is used as the data bus that read and/or write data to those units. PORT-D is reserved for UART. Initially, it is used for debugging during systems start-up. It can be modified to provide the central monitoring function for the entire systems.

All communication to the functional units via the PORT is asynchronous and level enable. Hardware Design The main circuit for this project is “Phone Line Circuit”. The Phone Line Circuit(s) are connected to Micro Controller, Decoder, Ring Generator and Telephone. Micro Controller sends or receives data via Share Data Bus by PORT-C and sends address to the decoder by PORT-A. The decoder receives the address, decodes the address and sends the control signal (Control Enable and Control Latch) to each Phone Line Circuit as shown in overall system diagram. The Phone Line Circuit(s) communicate with MCU by sending or receiving data via Shared Data Bus. MCU uses time sharing protocol to control each Phone Line Circuit by sending the address of the Phone Line Circuit to the decoder and sending control data to Phone Line Circuit via Data Bus.

Each Phone Line Circuit is connected to one telephone line. In this project, there are 4 Shared Audio Bus so we can expand the switching up to 8 lines.

The Phone Line Circuit supplies DC voltage to telephone. It receives signal from telephone, check the number by DTMF receiver and send the number to MCU when requested. Tri-State buffers are used to multiplex data from DTMF receiver and Off-hook detection relay of each Phone Line Circuit to Shared Data Bus. Tri-State buffer passes through the data when it receives Control Enable signal from Decoder. Because we use time sharing method the control signals sent from MCU to each Phone Line Circuit will be latched when the Phone Line Circuit receives Control Latch signal from Decoder. There are 3 sets of control signals from MCU to the Phone Line Circuit: 1. Tone Selection, select tone presented to telephone when off-hook (Dial Tone, Busy Tone, and Ring Tone), 2.

Audio Switch Control, control audio switch to connected phone line together for speaking, and 3. Ring Control, control relay switch ring signal to telephone line. The Audio Bus is used to link each phone line together when there is calling. Coil and capacitors are used to separate analog signal from DC Supply voltage. There is one off-hook detection 2-contact relay in each Phone Line Circuit. When telephone off hook the relay will close and pull the off-hook detection output down to GND and switch the audio channel from ringing mode to audio mode.

DTMF CIRCUIT:

Explanation of EventsA) Tone bursts detected, tone duration invalid, outputs notupdated.B) Tone #n detected, tone duration valid, tone decodedand latched in outputs.C) End of tone #n detected, tone absent duration valid,outputs remain latched until next valid tone.D) Outputs switched to high impedance state.E) Tone #n + 1 detected, tone duration valid, tone decodedand latched in outputs (currently high impedance).F) Acceptable dropout of tone #n + 1, tone absent durationinvalid, outputs remain latched.G) End of tone #n + 1 detected, tone absent duration valid,outputs remain latched until next valid tone.Explanation of SymbolsVIN DTMF composite input signal.ESt Early Steering Output. Indicates detectionof valid tone frequencies.St/GT Steering input/guard time output. Drivesexternal RC timing circuit.

Q1-Q4 4-bit decoded tone output.StD Delayed Steering Output. Indicates thatValid frequencies have been present/absentfor the required guard time, thus constitutinga valid signal.TOE Tone Output Enable (input). A low levelShifts Q1-Q4 to its high impedance state.tREC Maximum DTMF signal duration notdetected as valid.tREC Minimum DTMF signal duration requiredfor valid recognition.tID Minimum time between valid DTMF signals.tDO Maximum allowable drop-out during validDTMF signal.tDP Time to detect the presence of validDTMF signals.tDA Time to detect the absence of validDTMF signals.tGTP Guard time, tone present.tGTA Guard time, tone absent.

TRUTH TABLE:

CROSS POINT SWITCHING:

CROSS POINT SWITCHING:

Figure 1 shows the reference design for a 16 × 16 cross point switchArchitecture. This cross point switch is divided into three major categories:Switch matrix, configuration, and address decoder.

Fig: 16 X 16 Cross point Switch Architecture Reference Design

Fig:16 X 16 Cross point Switch Reference Design Hierarchy

Switch Matrix

The switch matrix only has input, output, and multiplexer select pins. You

can connect all 16 inputs to the multiplexer of each output, allowing youto independently connect any output to any input and any input to any orall outputs. Figure 3 shows the basic circuit of each output cell.

Fig: Switch Matrix Circuit Output Cell

You can always add features to the output cell (e.g., addingAnother tri-sate buffer or register at the output of theMultiplexer).

Address DecodersYou can use an address decoder to decode the output address so that onlyone output cell is enabled for configuration. Table 2 shows the output ofthe decoder and the enabled output cells for a 16 X 16 cross point switch.

4 Altera Corporations

The name of the address decoder reference design file isdecoder.v. The QuartusII software synthesizes the decoder,Allowing you to use the product-term logic in the MAX 3000ADevice or in the look-up table (LUT) in the MAX II device toCombine the decoding with other functions.ConfigurationConfiguration is the main feature in a cross point switch. As shown inFigure 1 on page 2, the configuration module consists of a double rowregister architecture, which allows reconfiguration of input to outputconnections during operation. Activation of the new configuration occurswith a single configuration pulse.The switch matrix circuit is controlled by data in two sets of 16, 4-bitregisters — the LOAD REGISTERS and CONFIGURATION REGISTERS.You can use the four bits of each register to store the input address thatidentifies the input that you can connect to a particular output. Table 3shows the connection of an input to a particular output when you select adifferent input address.

You can select one of the 16, 4-bit registers in the first set of LOADREGISTERS by placing a 4-bit word on the output address bus You can place data that is written into the loadregister on the input address bus. The load register contains the 4-bitaddress of the input that connects to that output. The load register stores

input data at the low-to-high transition of the load input pin with thechip-select (cs) signal set to high. The contents of the load registers arethen transferred to the second set of CONFIGURATION REGISTERS at thelow-to-high transition of the cnfg input signal with the cs signal set tohigh. This transition sets the state of the entire switch matrix to the chosenconfiguration.Reset mode is also supported in this 16 X 16 crosspoint switch. When youassert the reset (res) signal (with cs set to high), the entire crosspointswitch is in its initial state where all outputs are connected to input0.

LOGIC DIAGRAM:

PROCEDURE:

USER FEATURES

The extension numbers are

• 3, 4, 5, 6

Making an intercom call

• Lift the hand set

• Dial the desired Intercom Number

Making an Outside call

• Lift the handset

• Dial 0

• Get P&T dial tone

• Dial the desired number

Holding a call

• While connected in speech with a trunk call

• Dial Flash

• Other end receives hold on music

Retrieving a held call

• While getting feature tone,

• Dial Flash

Making a screened transfer

• While connected to an outside line,

• Dial Flash

• Dial the desired extension number

• Wait to be answered and announce the call

• Hang up to complete the call transfer

Making a unscreened transfer

• While connected to the outside line,

• Dial Flash

• Dial the desired extension number

• Hang up to complete call transfer

Last trunk number redials

• Lift the handset

• Dial 8

• The last number dialed in trunk will be dialed out

Abbreviated Number Dialing To dial frequently called numbers stored in memory

• Number Dialing: #01/#02

Auto Call Back

• When the dialed Extension/Trunk which was busy is freed, both of you will get the

ring

• Lift the handset

• Dial the desired Extension Number/Trunk Number, get busy tone

• Dial 7 2

• You will get feature tone and then hang up

Alarm Setup

This feature allows you to remind the time

• Dial 116+HHMM

HHMM – Time after which the alarm should ringAlarm Cancellation To cancel the alarm

• Dial 116+0000

Barge inIt is the feature used to have speech with the extension which is busy with another.

• Lift the handset

• Dial 786+Ext.No

• Get speech connected with the busy extension

Call Pickup

• You can pick up the call meant for others ringing in other extension

• Lift the handset

• Dial 2

Conference

• The system allows you to make 3-party conference

• Lift the handset

• Call the extension number(first party) Dial flash

• Dial the internal extension number(second party)

• When the second party answers, Dial Flash

• Get feature tone. Dial 7 and speech gets connected with both of them

Caller ID

• ID Display for intercom calls

1111+Ext no (calling)

• ID Display for incoming call transfer:

P&T No+11+Ext no (transferred)

• ID Display for outgoing call transferred:

P&T No+00+Ext no (transferring)

• ID Display for intercom calls transferred:

Ext no in hold + 111+ Ext no (transferring)Do not Disturb

Feature that avoids the extension call from disturbing you

• Lift the handset

• Dial 7 1 6 and your extension number

• You will hear music tone and hang up

Feature cancellation

• To cancel the features auto callback and do not disturb

• Lift the handset

• Dial 7 9

• Get music tone and hang up

Hotline

Feature that fetches the trunk automatically when you lift your handset

• Dial 111+1-7 secs

1-7 – delayed secsHotline cancellation

• Dial 111+0 for hotline feature cancellation

• Flash +0 for current hotline exit

P&T waiting call Pick Up

• To use the waiting call pickup feature in P&T line [BSNL] through EPABX while in

speech with trunk,

• Dial Flash 8+Number

SYSTEM OPERATION SETTINGSSupervisory features can be programmed from any Intercom port.The supervisory code is 98679.This code must be dialed for each setting

System Default Setting

• Dial 9 8 6 7 9 0

• Get music tone

Default Setting Ext class of service - level 5 Trunk type - pulse Round robin time - 20 secs Executive ringing - Disable Ringing sequence - 3,3,3,3 Abbreviated dialing - Disable Caller ID - Disable Do not Disturb - Disable Hotline - Disable

Extension class of service

• Dial 9 8 6 7 9 1+Ext no+ Level

• Get music tone

• Ext.Number – 3, 4, 5, 6

• Level

0 – Not connected 1- Intercom only 2- Local with 98 & without 95 only 3- Local with 98 & 95 & without STD 4- Local with 98 & 95 & STD

5- Local with 98 & 95 & STD &ISD 6- Local without 98 & 95 & STD &ISD

If extension 3 is given not connected, it will be changed to intercom only when the system is switched ON.Trunk Type Selection

• Dial 9 8 6 7 9 2 + Type

• Get music tone

• Type

1-Pulse 2-ToneRound Robin Time Programming

• Dial 9 8 6 7 9 3 + Time in secs [2 digits]

• Get music tone

• Time

00 - Simultaneous ringing06-99 - Round robin ringing

Executive Extension Programming

• Dial 9 8 6 7 9 4 + Ext no + option

• Get music tone

Option -> 0-Disable 1-EnableRinging Sequence Programming

• Dial 9 8 6 7 9 5 + E1 E2 E3 E4,

• Get music tone

• E1,E2,E3,E4 – Extension numbers 3/4/5/6

• For fixed Landing, give the same Ext.No in all position

Caller ID This is used to display the id of the calling number, both extension and P&T

• To enable caller ID function

9 8 6 7 9 6 + 0/10 - Disable1 - Enable

To store frequently called numbers using Specific codes To enable or Disable Abbcos

• Dial 9 8 6 7 9 7 + Ext No + 0/1

0 – Disable1 – Enable

• Number Storage:

9 8 6 7 9 - #01 – P&T no #9 8 6 7 9 - #02 – P&T no #P&T numbers stored should be less than 16 Digits

FAULT SWITHES:

HOOK UP RINGER:

Disable the incoming volume tone and all other ringer function for the extension terminal no.3

HOOK UP DIALER:

Disable the dialing tone and outgoing facility to the extension no.3, [to activate the fault make the fault switch in fault position and reset the unit, this fault switch has no effect once the call has been connected.]

POWER FAULT:

Total EPABX feature is activated, [i.e EPABX is dead] only the extension terminal no.3 is act as a individual telephonic instrument.

CROSS POINT SWITCHING POINT:

This fault will disable all the switching transfer function of the EPABX such as call transfer, intercom calls etc..

DTMF FAULT:

This fault will disable the dialing facility and will deactivate the main DTMF telephonic unit.

CONTROLLER FAULT:

This fault is similar to DTFM and CROSS POINT SWITCHNING fault, this fault will make the total EPABX unit inactive.