Introduction

The electric doorbell is a simple circuit that triggers a sound on the completion of circuit by pressing the button. It is this simplicity that makes doorbell such a marvel. The simple devices in the doorbell put the scientific principle of electromagnetism into action in a useful way. In order to understand the operations of an electric bell, you should first need to understand what is an electromagnet. Well, to put it in simple words, an electromagnet is basically a type of magnet in which the magnetic field is produced with the help of an electric current. When any electrical influences electromagnet it works as a standard magnet (generating magnetic fields). When the power generation to an electromagnet stops, the production of the magnetic field also stops.

So, in an electric bell, an electromagnet forms an important part along with Armature, Spring, Armature rod, Hammer and a Gong.

The image below shows the internal mechanism of an electric bell.

An electric source, for example, a battery can be used to power the electromagnet used in an electric bell. The electric circuit is completed by installing a push switch which you can press to generate sound in an electric bell. The switch also acts as the circuit breaker.

So once the setup is completed, when the switch is pressed, the circuit loop is complete which causes the current to flow through the circuit. The arm which strikes the gong is connected to spring at one end and an iron ball at the other end. This is called a hammer or a striker. The arm is attached to an iron strip which is attracted to the electromagnet when the circuit is complete and the current flowing through it.

Why does this happen? It’s mainly because the magnetic field created by the electromagnet attracts the iron strip towards it when the circuit is complete. This is the moment when you hear the ringing sound since the hammer keeps hitting the gong. Meanwhile, at its rest position, the hammer is held away from the gong on account of the spring attached to its arm. This is an anchored arm.

Process of the working of an electric bell

Now that you have an understanding of the important parts in an electric bell, the step-by-step process of the working of the electric bell is described below:

• The switch is pressed and current flows through the circuit.
• The electromagnet is powered and generates a magnetic field that attracts the iron strip towards it.
• The striker strikes the gong (bell).
• When the striking arm strikes the gong, the contact is broken and current stops flowing through the circuit.
• This causes the electromagnet to lose its magnetic field.
• The connected spring arm returns the striker to its original rest position.
• The contact is restored and current flows through the circuit (provided the main switch is still pressed).
• The process is repeated from the beginning.
• Simulation of model is done in matlab/simulink with outputs of position of plunger,pulses given and velocity of plunger moment during on and off.
• 
• Pulse generator has time period of 4 sec and 50 percent on period hence the switch is closed for 2 seconds and then released.
• A battery is connected to a solenoid whose plunger moves upon applicaion of potential(voltage)
• From the graph we an understand that he plunger intial position was at 2 mm and when the pulse is passed or swith is on the plunger is ar 0 mm and rings the bell and when the switch is off the plunger moves to 5 mm
• And also we can observe the velocity of plunger at that instantaneous point of time from the last plot

  2. Use a thermistor to sense the temperature of a heater & turn on or turn off the fan as per below conditions:

  Temperature source: 20 °C from 0 to 10 seconds, 27 °C from 10 to 30 seconds, 23 °C from 30 to 50 seconds

  Fan conditions: ON if the temperature above 25 °C, OFF otherwise

  COMPONENTS USED

• Heat Generating Device: System based heat generating unit is implemented to generate and vary the heat as per required for analyzing the speed of fan wrt tochange in temperature.

• Positive dc Supply : This block represents an idealpositive supply rail. Value of this parameter is set to
  12V wrt to Electrical Reference Block.

• Thermistor: This block represents an NTC thermistor having B-parameter equation where temperature is governed by equation. m*c*dT/dt = Q where Q is the net heat flow into port A, m is the mass and c is the lumped specific heat capacity. The resistance is established from equation R(T) = R0*exp(B*(1/T1/T0)).

• Resistor: The voltage-current (V-I) relationship for a linear resistor is in general represented as V=I*R, where R is the constant resistance in ohms. The positive and negative terminals of the resistor aredenoted by the + and - signs respectively.

• Solver Configuration: This represents solver settings to be used for simulation. Various parameters involved in it are tolerance value, solver type and algebra to be used, iterations etc

• PS- Simulink Converter: This block is converts the input Physical Signal to a unitless Simulink output signal.The unit expression in 'Output signal unit parameter must match with the unit of the Physical Signal and determines the conversion.

• Switch:With Fan conditions: ON if the temperature above 25 °C, OFF otherwise
• Signal builder waveform is as shown it is converted fron centigrade to kelvin by adding 273.15 to centigrade value.
• 
• The simulink model of the fan controlled according to temperature is shown
• The output waveform shows that from 0-10 seconds the fan is off and from 10-30 seconds it is on(i.e above 25 degree centigrade) and again it is off from 30 -50 seconds