Microcontroller Based Versatile STD-PCO Call Monitor Laxman Singh1, R.B.Dubey2 and Dr. S.k Sharma3 National Physical Laboratory, Dr.K.S. Krishnan Road, New Dehli-110 012 1 , 2, 3 Apeejay
College of Engineering, Sohna , Gurgoan , Haryana
E-mail of corresponding author:
[email protected]
Abstract Line interface: The line interface part is used A low cost microcontroller based STD-PCO call monitor has been designed & develop for the STD PCO booths .this STD PCO call monitor displays the no. dialed by the caller. It can be display the no. up to 20 digit it automatically detects the call maturity & displays the no. of calls on the basis of pre defined call rate of different STD no. it also display the amount in rupees. As soon as receiver is on hooked it continuously display the amount and time elapsed on the LCD display the circuit & the software have been described in this paper.
Key words: STD-PCO Monitor , microcontroller.
1. Introduction As telephone is still an expensive item in remote areas of India so PCO centers are setup. Initially these PCO operates used stopwatch, calculator and list of STD/ISD codes with pulse rate (provided by the telephone department) to fill time spend and amount that caller should pay. As this leads to a lot of disputes and problems between pc o user and operators so this problem has been solved by the micro controller/ microprocessor based std/pock monitors. To under stand how this STD/PCO monitors works and also one can increase its capabilities and utility this STD /PCO monitor has been design and developed. The details of the system has been discussed in the present paper .
2. Hardware Design Hardware of the STD/PCO monitor can broadly be divided into three parts that is line interface and control cum display.
to interface or connect the PCO monitor to the p and t line. It can be further divided into following subsection: (i) Hook sensing section: when the hand set is lifted from the hook or when handset is replaced on the hook , this information is send to the control section by the hook sensing section (ii) Ring sensing section: This section is used to any incoming call on the phone line and give this information to the control section. (iii)Tone sensing section: This section is used to sense the dial- tone appearing on the telephone line. Currently almost all telephone and exchanges supply two types of dialing that is pulse dialing and tone dialing. The tone dialing is also known as “fast dialing”. (iv) Line reversible sensing section: Normally the voltage on the telephone line +40 volts. When we lift the hand to dial a number, this voltage changes to + 12 volts. When the called property lifts the handset to answer the call, this voltage changes to -12 volts. This line reversal /changes sensed by the line reversal sensing subsection of line interface section. To start meter, this information is passed on to the control section of the PCO monitor. (v) 16 KHz signal sensing section: The line reversal sensing does not always provide correct information for the metering and this leads to problem between customer and PCO operator .so, instead of using a
line reversal method to start the method, a 16 KHz signal received from the exchange is used by the current PCO monitors to state the metering process. This 16 KHz is passed to the control section of the PCO monitor for metering purpose. When 16 KHz signal is received from the exchange, it is compared with the 16 KHz signal locally generated by the PCO monitor and when these pulse match the meter is increased by one. Main / control section: This is the brain of the PCO monitor. It receives various signals from different section from different section and based on those signals, sends out various signals to the different sections connected tom it. The main input to this section comes from the line interface section and output of this section goes to LCD display. This control section itself divided into the following subsections. (i) CPU section: This is real control section of the PCO monitor; this section keeps control over various functions of the PCO monitor. the signal received by line section DTMF section are giving to the CPU section to take proper action .once the input signals are received, this CPU section , based on the set of instructions stored in its memory, gives out different instructions to the display section, these instructions could be display some message. (ii) DTMF section: Tone sensing subsection of the line interface section sends to a tone signal received from the phone line, DTMF stands for “dual tone multi frequency” , which is also known as tone dialing or fast dialing because this method is used to dial the required number very fast, compare to using the pulse dialing method. The block
pulse is provide by the exchange to the PCO monitor when the called party lifts the handsets. This information diagram of the hardware circuit is shown in figure1.
3. Software Description The detail of the flow of the software is given in the figure2. At power on the microcontroller initializes all the required parameters and LCD display. There after it waits for the receiver of the phone to be off hooked. As soon as the receiver is off hooked it jumps to the DTMF routine and waits for the number to be dialed. After dialing of the numbers the microcontroller then waits for the maturity of the cell. As soon as this is matured it checks the city code and selects the pulse rate of that city. There after it goes on incrementing the pulses at the same time and also calculates the amount for those number of pulses and display the same on the LCD screen when the caller on the hooks the receiver the total amount is continuously displayed on the LCD screen and the increment on the pulses is stopped after pressing the reset button the microcontroller starts the program right from the beginning,
References: 1. A.J.Caristi, Electronic Telephone Projects, Howard W.Sams & Co. Inc. USA, 1989 2. F. Zapf, Telephone Controlled Switch, Elektor India, Vol. 2, pp 96-102, 1994
APPENDIX 1: LINE INTERFACE SECTION MAIN/CONTROL SECTION Figure 1: Block Diagram of the developed Circuit
APPENDIX 2: Figure 2: Flowchart of the developed software
