MICROCONTROLLER BASED TELECOM SWITCH

SPONSORED BY: ARJ ASIA

External Guide: Mr. Jitendra Date

Internal Guide: Mr. M.B. Tirmare

By: Neha Purandare

Janhavi Shah

Sonali Shelke

PROBLEM: A "telephone solicitation" is a telephone call that acts as an advertisement. Even if you have an unlisted, non-listed, or non-published telephone number, you may still receive unsolicited telephone calls with automated or prerecorded messages. In some cases unlisted or non-listed numbers can be obtained from a directory assistance operator. They, along with non-published numbers, may be sold to other organizations or people with whom you have done business. Some sales organizations call all numbers in numerical order for a neighborhood or area.

SOLUTION:

In the field of telecommunications, a telephone exchange (US: telephone switch) is a piece of equipment that connects phone calls. It is what makes your phone calls "work" in the sense of making connections and relaying the speech information. Here we are  using our telecom switch to connect only the right call and block the unwanted ones.

BLOCK DIAGRAM

EXPLANATION OF BLOCK DIAGRAM

DTMF Encoder:

The DTMF encoder resembles the telephone set. It uses DTMF encoder integrated circuit, Chip UM 91214B . This IC produces DTMF signals.

DTMF Decoder:

It consists of MT8870D chip which is a direct DTMF detector. Its output is a 4- bit BCD code; each 4 bit code corresponding to a DTMF tone pair. Whenever a valid tone pair is detected at the input, the StD pin goes high indicating that the tone pair has been latched.

• Microcontroller:

PIC18F452 accepts the 4 bit BCD code from MT8870D and checks if the DTMF tone pair stands for numbers between 0 to 9. If it does, it is considered a valid no. and the user is allowed to receive the call; else it is routed to voice chip and rejected.

ISD2560 Voice chip:

If the call is unsolicited one, the P/R bar pin of this chip is pulled to Vcc and a message rejecting the call is played back to the caller. The message is pre-recorded on the chip by manual switching of P/R bar and CE bar pins.

Features of PIC18F452

• 16-bit wide instructions, 8-bit wide data path

• Linear program memory addressing to 32 Kbytes

• Linear data memory addressing to 1.5 Kbytes

• 100,000 erase/write cycle Enhanced FLASH program memory typical

• 1,000,000 erase/write cycle Data EEPROM memory.

• Low power, high speed FLASH/EEPROM technology.

• Wide operating voltage range (2.0V to 5.5V)

• Watchdog Timer (WDT) with its own On-Chip RC oscillator for reliable operation.

• Programmable code protection

Features of MT8870D

• DTMF Receiver• Low power consumption• Internal gain setting amplifier• Adjustable guard time• Central office quality• Power-down mode• Inhibit mode

FEATURES OF ISD2560

• Easy to use, voice

record/playback solution.• Single chip with 60 sec duration• Manual switch or uC compatible.• Auto power-down (push-button)

mode• Can handle multiple messages• On-chip clock source• Single +5 volt power supply

FLOWCHART

START

ACCEPT INPUT TONES FROM MT8870D

IS StD=1?

A

N

Y

A

IS TONE BET 0 TO 9?

Y

N

MAKE RD0 = 1

MAKE RD1 = 1

STOP

SOFTWARE

• Development Environment:

The MPLAB C18 Code Development Systems are complete ANSI ‘C’ compilers for Microchip’s PIC18CXXX family of microcontrollers. This compiler provide powerful integration capabilities and ease of use not found with other compilers.

• Programmer: PICSTART Plus Entry Level Development Programmer

The PICSTART Plus development programmer is an easy-

to-use, low cost, prototype programmer. It connects to the PC via a COM (RS-232) port. MPLAB

Integrated Development Environment software makes using the programmer simple and efficient. The PICSTART Plus development programmer supports all PICmicro devices with up to 40 pins.