Week -2

1. AIM

1. Make a Simulink model of Doorbell using a solenoid block.
2. Use a thermistor to sense the temperature of a heater and turn the fan on or off as per the conditions.

2. OBJECTIVE

• To create a block model of doorbell using a solenoid block and try to simulate it.
• To understand what a thermistor is and to find the threshold value at which the fan will be turned on and off at any other condition.

3. METHOD

3.1 Simulation of Doorbell using a solenoid block.

• A doorbell is a signaling device having electric and mechanical components.
• The sound is produced when the electric current passes through the circuit.
• In this simulation, we try to produce the sound in the bell using a solenoid when the switch is closed.
• The basic functioning of the bell is, when the electric current flows through the electromagnet it produces an induced current that moves the plunger and the bell rings.
• As per the given condition, we need the bell to ring for 2 secs and then stop. So for this, we use a pulse generator so that we get the required signal in continuation.
• We adjust the inputs of the pulse generator such as amplitude, time period, pulse width, and phase delay such that it produces the necessary pulse.
• A solenoid is a device comprised of a coil of wire, the housing, and a moveable plunger (armature). When an electrical current is introduced, a magnetic field forms around the coil which moves the plunger. In short, converts electrical energy into mechanical work.
• The battery is used as the current source which is required to run the simulation.
• All the circuits need to be grounded to maintain the potential difference so that the current flows.
• To check the motion of the plunger we add a Transitional motion sensor and then we change the initial position of the plunger from 0 to 5cm.
• We add scope to check the motion.
• We add a solver so that the software understands what needs to be done.

we change the parameters of the solenoid to match our requirements.

we change the initial position of the plunger.

	We see a small delay in the plot. This delay is caused when the plunger is disconnecting from the bell but is still in contact with it.
Fig. Change in position of the plunger

3.2 Using a thermistor to sense the temperature in a Heater and turn the fan ON or OFF.

• A thermistor is a resistance thermometer or a resistor whose resistance is dependent on temperature.
• The conditions given to us are used for the input signal. We use a signal builder for this. The three temperatures are added according to the timings which are 20°C from 0 to 10 secs, 27°C from 10 to 30 secs, 23°C from 30 to 50 secs.
• Since the thermistor won't understand what the input is so we add a controlled temperature source.
• The output of the source is given as an input to the thermistor.
• The positive end of the source is connected to the positive of the thermistor and then the negative end of the source is grounded to create a potential difference.
• We add another resistor in series and connect a voltage sensor to it so that we can measure the value of the threshold. The sensor converts the electrical signals into a physical signal so that we can get a threshold value.
• A battery is also added so that we can run the circuit. It's also grounded to create a potential difference and we also add the solver.
• The condition to turn the fan ON is that of temperature above 25°C and for other lower values the fan must remain OFF.
• So we add a switch block that acts as an if-else loop and gives the threshold condition of the threshold voltage we got across the resistor. Where the output ON will be given at 0 and OFF will be given at 1.
• We add a display and scope to check when the fan turns ON during the 50 secs the simulation is run for.

The threshold value which we get across the resistor which determines the ON-OFF condition for the fan is added to the switch. The threshold value obtained through the voltage sensor is 0.01099.

The signal builder input is given as per the conditions. The three temperatures 20°C from 0 to 10 secs, 27°C from 10 to 30 secs, 23°C from 30 to 50 secs are converted to kelvin and added in the signal. The fan will turn ON only between 10 to 30 secs.	From the plot, we confirm that the circuit is working properly and we are getting the desired output. From 0-10 secs the fan is OFF, from 10-30 secs the fan is ON, and again from 30-50 secs the fan is OFF.

4. LEARNING OBJECTIVE

1. To understand how the solenoid works and then using that create a block model of the doorbell in Simulink.
2. To simulate how the fan turns on or off for the given conditions.
3. To learn the working of the thermistor and learn how it's used to control the fan according to the inputs.

5. CONCLUSION

In the first part, we simulate a doorbell using a solenoid. A solenoid is used to convert electrical energy into mechanical energy. So we create a block diagram according to it. A slight delay is observed in the plot which is a delay time the plunger takes when it moves away from the bell.

In the second part, the simulation turns the fan ON above 25 °C, so during 10 to 30 secs the fan is turned on since the temperature is 27 °C and for 0 to 10 secs and 30 to 50 secs the fan is turned OFF since the temperatures are 20 °C and 23 °C which is below 25 °C.