Telephone Operated Display System

Dual tone multiple frequency or DTMF is a method for instructing a telephone switching system of the telephone number to be dialed or to issue command switching system or related telephony equipments.The DTMF system uses eight different frequency signal transmitted in pairs to represent sixteen different numbers, symbols and letters. The frequency used where choosen to prevent any harmonics from being incorrectly detected by the receiver as same as other DTMF frequencies.Using the concept of DTMF frequencies, telephone can be used for controlling motors,controlling the door, home automation, etc. thereby multitasking the existing telephone. We also see many displays in banks, hospitals, etc which is used to calling persons. These displays are comparitively expensive. In this project we develop a circuit for telephone operated display system, by incorprating a display and a telephone.When we need to call a person amongst many standing outside the cabin, just lift the telephone handset of the cradle and press the respective number. The number of the person called will be displayed and a bell will sound to inform the person that it is his turn. This circuit is very useful for doctors to call the patients waiting outside. It is also used in banks to call the customers. It is also used in quiz competitions for calling the participants. This device is also useful for hearing and visually impaired persons.Some of the existing systems similar to telephone operated calling system are there now a days. Some of them are remote token display and sound system, remote token display system using microcontroller, nurse call system.The proposed system is the telephone operated display system.this system converts the DTMF signal to its binary equivalent. This circuit consist of a DTMF receiver ic which converts a dtmf input signal in to its binary equivalent. This signal is decoded and displayed as its decimal equivalent through decimal display unit. It also provides a sound alerting signal which informs a people that the number is displayed.

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