Denny Divayana(Alumni 2006)


Dosen Pembimbing :


Pembimbing 1 Drs. Jusuf Bintoro, MT

Pembimbing 2 Muhammad Yusro,SPd, M.T



This research aim to make display of telephone cost on a house which have some occupant, such as boarding house, with exploit microcontroller AT89S51. This research  conducted in Electronic’s labolatory of major  Technique electro, Faculty of  Technique, State of Jakarta University, at anomalous semester, year of academic 2005/2006 with labolatory experiment method.

This research use DTMF decoder, hook detector, ring detector and keypad as input, microcontroller as the processor, and also LCD and Chip Corder ISD as output. Keypad used as input for password and chosening menu, its connected on 3rd port microcontroller, hook detector as the detector condition of telephone’s hook for begin the input password and start the phone call that conect at 1.6th  microcontroller port , DTMF decoder give the input of pressed phone number on the port 1.0th – 1.3th, afterwards detected as lokal number or SLJJ number and counter the appropriate on rate. LCD will display information of date and time, select menu and display phone number and amount of telephone cost for each user. Chip corder ISD produce a sound message which used by user to guide them when operate the device.

The result show that  Cost Telephone Display With Common User System operate with correctly, indicated with LCD can display the data that require and count the cost telephone, also produce some sound message as guider from ISD.


Keyword: telephone, microcontroller, DTMF, LCD, ISD




Communication is a very important community needs . The development of technologies that facilitate communication continues to evolve to this day , especially long-distance communication . Phone is one such technology products .

Phone presence is needed , almost every home can be encountered especially in large cities . Not only at home but also in the private house where people do not have the family ties , for example boarding house . However, the use of the telephone in the house where people do not have a family relationship or a boarding house is not optimal , as in private homes .

Usually the phone is mounted in a boarding house used limited only to receive a call from outside , while to dial out , residents must go to the boarding house itself or the public telephone kiosks . This problem is due to the division of payments based phone itself . Since the number of phone users so that it would be unfair if the system used is evenly split the cost of the phone that will be paid . However, if the phone is mounted in the boarding house only to receive calls only, then placing the phone less than optimal and efficient , especially for residents of the boarding house , which had to be painstakingly searching for kiosks or phone to make a call .

The above problem can be anticipated if there is a system that can record phone usage per user , so someone will pay the phone bill in accordance with its use . The system will be built require a controller which handles all existing problems . This problem is the use of a recording pulse and phone number usage by grouping each user , so there is no injustice in the payment of telephone charges .

With the presence of the microcontroller is quite widespread use these days as AT89S51 microcontroller which has its advantages can be programmed and operated to process data like a computer , but have much smaller dimensions , efficient in the use of electric power and an affordable price . So with excellence was expected to answer all of these problems . For that sought to create a tool that can record each user’s telephone usage charges are based on microcontroller AT89S51 .





Microcontroller AT89S51 is MCS – 51 , ​​in addition to 89S51 there are several other types of MCS – 51 which has the characteristics and different abilities , including the microcontroller 8031 , 8051 , 8751 , 8052 , 89C51 , and 89SXX . The development of increasingly rapid AT89S51 microcontroller , besides due keefisienannya level that has flash memory that can be reprogrammed with a very easy and low power consumption , as well as the system in the charging process of the program by using the In- System Programming . The minimum system so the system can be used as a downloader . Here are the features that are owned microcontroller AT89S51 :

• Compatible with MCS – 51 microcontroller

• 4K bytes Downloadable Flash Memory

• Operating Voltage 4.0V to 5.5V

• Frequency range 0 Hz to 33 MHz

• 3 level program memory lock

• 128 x 8 – bit Internal RAM 32 Programmable I / O Lines

• 2 timers / counters 16 -bit and 6 pieces of Interrupt Sources

• Full Duplex Serial Channel

AT89S51 microcontroller has 40 pins fruit . The composition of microcontroller AT89S51 pin shown in the following figure .










Figure 1 . Diargam Pin Microcontroller AT89S51

Special function AT89S51


              Timer / Counter

Device Timer / Counter is an integrated hardware AT89S51 microcontroller , used to access specific registers are stored in the SFR . In microcontroller AT89S51 are 2 timers / counters Timer 0 and Timer 1 . Counting binary Timer 0 TL0 and accessed through registers TH0 , binary counter Timer 1 registers accessible through TL1 and TH1 .

Enumerators binary Timer / Counter AT89S51 is a 16 -bit binary counter rising (count up binary counter ) that counts up from 0000H to FFFFH , when the enumerator conditions changed from 0000H to FFFFH back there will be a signal overflow ( overflow ) .

To set the working timers / counters are used 2 additional registers that are shared by the Timer 0 and Timer 1 . Registers are additional TCON register ( bit addressable ) and TMOD ( not bit addressable ) .

In addition to the timer , Timer / Counter can serve as input for the interruption . Interrupts Timer 0 and Timer 1 is generated by TF0 and TF1 , appears overflow occurs when each timer ( except the timer 0 in mode 3 ) . When the timer interrupt occurs , the microcontroller would zero out the signs ( TF0 danTF1 ) .




AT89S51 has 5 pieces of interruptions , ie two external interrupts , two timer interrupts and the serial port interrupt . Each interrupt source can be enabled and disabled individually by setting the relevant bits in registers IE and set the priority level of each interrupt in the IP register .

Interruption is a program that interrupts the program being worked when the interrupt condition is met . And going back to the previous program while getting instruction RETI . Terms interruptions determined by the type of interruptions . If the timer interrupt is enabled, an interrupt will work when TF1 or TF0 logic high . If the external interrupt is enabled then the logic condition that occurs in P3.2 ( External Interrupt 0 ) and P3.3 ( External Interrupt 1 ) is a prerequisite for the occurrence of interruptions . Form of the condition which is a requirement set by the interrupt IT0 and IT1 in register TCON contained . And if the interrupt is enabled, the serial port is the current condition of RI and TI logic high ( when completed receiving or sending data) .



The word ” telephone” is derived from the Greek words ” tele ” , which means far , and ” phone” , which means sound . With our current understanding , telephony ( telephony ) covers conversion ( change ) of the sound signals into electrical signals that the audio frequency can then be transmitted via an electrical transmission system , and finally converted back into sound pressure signals at the receiving end . These phone systems can be divided into several categories , according to the variance ( mode ) is used , and currently most systems provide two-way communication according to any one of the following two ways .

Simplex system allows transmission in one direction only for a certain time , but also provide two-way communication alternately ( arternately ) . Duplex system allows transmission in both directions at once . It can simply be implemented by providing two separate circuits , one circuit for each direction , but it is not economical because of all the facilities to be made in duplicate . Duplex phone system means the simultaneous transmission through a couple wires together without the need for switching .

The development of the phone when the phone is in the process of switching ( switching ) many uses digital techniques are also used for purposes other than transmission . The use of digital techniques to bring efficiency will be felt both the transmission system and switchingnya system , in which signals are transmitted messenger or connected in digital form , digital switching systems in a way to build relationships reconstitute Pulse Code Modulation ( PCM ) and connecting the appropriate with calls and requests can also skip the other digital signals other than PCM signals .

To initiate a phone call , then an operator must pick up the handset from its normal position in terms of the so-called off – hook , off – hook conditions for a sign to be ready to accept a central telephone number to be called by the operator . After the appropriate receiver circuit connected to the channel , the central will send a dial tone to the operator who will then play the desired number , some tone frequencies in a frequency region is sent to a central voice when the button is pressed . The tones are generally called Dual Tone Multiple Frequency ( DTMF ) , because every time a button is pressed, the two tones will be sent simultaneously to the channel . Then the caller will receive a notification from the central state of dialed numbers , either with a dial tone , busy tone , busy tone or tone other special tools .




This study utilized AT89S51 microcontroller to build a system that combines the MT8870 DTMF receiver , detector Hook , telephone ring detector that gets input from the telephone line , and an LCD keypad as input and as output ISD2500 Chip Corder .

The system will be made is the provision of debit pulse for Rp . 50,000 , -/bulan for each user that will be paid by the users ( residents of the boarding house ) along with payment of rent boarding house . Like the mobile phone that uses postpaid card , debit so each user has a pulse that will continue to decrease every make calls .

Each user must enter the code before calling certain ( password ) to be called . Each user has its own code that will meloading ( take ) the data owned by the user , in the form of pulses remaining debit amount . If the user enters the wrong code so he could not call .

The keyboard is used to enter the code ( password ) that is requested by the system and select the menu. There are two menus , the menu for the user and the menu for home owners ( administrator ) . AT89S51 microcontroller will process the entire process of storing and comparing that code , store data pulse debit each user, timing , and reduce the debit pulse each user every time you make a call . DTMF receiver is used to translate the phone number is pressed on the phone and send it to the microcontroller for identification purposes suppressed if the number is local or long distance call, which will affect the cost of the call . As we can use the LCD display to show the remaining credit debit , destination phone number and length of talk time to be carried out by the Internal timer microcontroller , the system timer . As long as the system works in addition to the LCD that displays instructions and data , ISD2500 issued instructions that make it easier for a voice in the operation of the system .




The equipment used consisted of

1 . Multimeter to measure the voltage, current , test lines and cable connections on the PCB equipment / circuit .

2 . Personal Computer ( PC ) and cable ISP ( In – System Programming ) is used for charging the flash memory microcontroller AT89S51 .

3 . Telephones and telephone line , is used to provide input data to the DTMF receiver , hook detector , ring detector .

4 . Stop watch brands of Mobile Phone Nokia type 2100, used as the test of time in the program made




The study was conducted by a laboratory experiment . By observing karaktesitik phone line , that is when the phone is picked up and placed on the hook , and when the phone rings . And test circuit reciver hook DTMF detector , ring detector , LCD , ISD , as well as create a program that can build a system as described in the frame of mind .




The survey results revealed that the phone line will have a voltage of ± 50 Vdc when the phone is placed hook and a voltage of ± 8 Vdc while the hook is removed, and when removed there is a current of 20 mA is sufficient to turn on the LED in the optoisolator . And when the phone rings there is an AC voltage on the telephone line .

So with the above conditions , a series of hook and ring detector detector that uses optoisolator can detect changes in telephone line and converts it into a digital two conditions , namely low and high .

From the test results on the DTMF receiver is known that the output of Q1 – Q4 generates correct binary data for each digit is pressed , eg when pressing the number 3 then the resulting binary data is 0011 . Meanwhile Valid data generated on the Std pin logic high only when keystrokes and return to logic low , it functions to determine when the system ( microcontroller ) to read the data issued from Q1 – Q4 .

Testing the ISD and the LCD that serves as the output can be observed from the output in the form of a visual display and sound right as desired .




From the results of tests performed can be concluded that the sequence that serves as an input to provide the right data to the system , and the system can work properly with the correct outputs on the LCD and ISD . So in general it can be concluded that this tool can work well .




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