CALLBELL WITH WELCOME DISPLAY Submitted b y SHAIK KHADEER 09QQ1A0434 SYED AMEER SOHEL 09QQ1A0437

INTRODUCTION 1. The Project “CALL BELL WITH WELCOME DISPLAY” derives its name from its operation. The circuit produces a buzzing sound and display’s a message “WELCOME”, whenever the switch is pressed. 2. This is a simple circuit and can be used at our homes, to greet our visitors with a flashing message right at the door/gate, with the press of a switch. 3. The circuit is built around two IC 555 timers, which acts as monostable multivibrators, each.

The circuit can be divided into two parts: i. The controller: The controller, provides triggers for the two IC’s, from whose outputs the buzzer and the Display are connected. ii. The Display: The display circuit is used to display the output “WELCOME”.

“WELCOME”, and are connected to the positive supply, as a result of grounding the corresponding pin, the circuit glows producing the message. 8.The monostable multivibrator remains in the on state for 5sec, then it returns to off state without any apply of triggering. At this point, the transistor switch is turned off, and the ground connections to the display circuit is disconnected, so the display is turned off.

COMPONENT DESCRIPTION Light-emitting diode : 1. A light-emitting diode (LED) is semiconductor light source.LEDs is used as indicator lamps in many devices and is increasingly used for other lighting. 2.The LED consists of a chip of semiconducting material doped with impurities to create a p-n junction. 3.As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. 4.Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron.

meets a hole, it falls into a lower energy level, and releases energy in the form of a photon. 4. LEDs emit more light per watt than incandescent light bulbs. Their efficiency is not affected by shape and size, unlike fluorescent light bulbs or tubes. 555 Timer IC: The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation, and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flip- flop element. Derivatives provide up to four timing circuits in one package.

Buzzer: 1.A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or piezoelectric. Typical uses of buzzers and beepers include alarm devices, timers and confirmation of user input such as a mouse click or keystroke. 2. An piezoelectric element may be driven by an oscillating electronic circuit or other audio signal source, driven with a piezoelectric audio amplifier. Sounds commonly used to indicate that a button has been pressed are a click, a ring or a beep. Alphanumeric Display LEDs 1. An LED display is a flat panel display, which uses light- emitting diodes as illuminating element.

They are typically used outdoors in store signs and billboards, in destination signs on public transport vehicles or even as part of transparent glass area. 2. A sixteen-segment display, sometimes called a "Union Jack" display or a "British Flag" display ], is a type of display based on 16 segments that can be turned on or off according to the graphic pattern to be produced. Common anode The alphanumeric displays use a "common-anode" connection. That means all the anodes--the positive connections,

have one point at which you can connect them all to the power supply's positive (+) output. You do not have seven positive pins, one per segment. Common Cathode The alphanumeric displays use a "common-cathode" connection. That means all the cathodes--the negative connections, have one point at which you can connect them all to the power supply's negative output. You do not have seventeen negative pins, one per segment

Operation: The circuit is built around two 555 ICs, and seven common-anode alphanumeric displays and a few discrete components. The circuit can be divided into two sections: Controller and Display. Controller: The controller section is built around IC1 and IC2, which are wired as Monostable multivibrators having time periods of 5secs each, we can change the time periods by changing the values of resistors and capacitors accordingly. Display: The display section is built using seven alphanumeric LED displays, which are wired to produce output message as

“WELCOME”, when powered. The display circuit is powered by a transistor which is connected to the output of IC2. Working: 1.The working of the circuit is simple, power on the circuit, the power indication LED will glow, indicating the presence of power. Press the call bell switch, which triggers both the timer ICs simultaneously. 2.IC1 produces a high output at pin 3 for about 5sec, transistor T2 conducts and the piezobuzzer sounds about 5sec, indicating that some body is at the door. At same time IC2 too provides high output at pin3 for about 5secs. Transistor T1 conducts to enable the alphanumeric displays. 3.The whole circuit is powered by a 9v battery, there is an on- off

switch provided to switch on and switch off the circuit whenever required. 4. In this experiment, the two transistors T1 & T2 acts as a switch, whenever, there is some base voltage, enough to drive the transistors, they conduct and create a path to ground for both alphanumeric displays, and piezo buzzer respectively. Applications: 1.This project can be used as a call bell for houses. This can be mounted outside of the house, in a well contained container or box, to prevent it from dust, rain... Etc. The switch can be projected upwards, and the buzzer and power switch can be placed somewhere inside the house.

This type of circuit can bring a type of happiness to the visitors, as the circuit displays a “WELCOME” message at their entry. Future Scope: 1.The circuit can be modified to work with a micro- controller, to display different types of greetings, when used with an lcd display or a panel of LED displays. 2.This simple circuit gives an idea about how timer ICs can be used in different applications, using this idea, we can built/develop a lot of different circuits which are more useful and also attractive, like a counter with flashing LEDs, digital clocks, in message displaying on panels and billboards … etc.