• Reducing voltage
• Temperature control
• Acting as a fuse
• Timing, Waveshaping, Filtering
• Pull-up and Pull-Down resistors
• Biassing active elements
• Terminating transmission lines
• Heating

This article shall take an in-depth look at each of these different functions of a resistor in a circuit. 

What is a resistor?

The electrical and electronic world is filled with many different components, and devices, each have a set of unique abilities. One of those components is the Resistor. The resistor is one of the most common components which you will find in almost every circuit. It is a passive electronic component whose main purpose is to provide resistance and limit the flow of current. The resistance of a resistor is measured in Ohms (Ω). The amount of current that is allowed to flow is determined by a resistor’s resistance level. A higher resistance means less current can flow, and a lower resistance results in more current flow. 

The resistance of the resistor is determined by Ohm’s law which states that the current through the resistor is proportional to the voltage across its terminals.

Common resistor functions in a circuit

Resistors are widely known for being able to limit the flow of current. But, there is more to this unassuming component than meets the eye. A resistor has many other functions in electrical and electronic circuits. 

Resistor function #1 in a circuit: Limit flow of current

The first function of the resistor is its main purpose; limiting the flow of current. So, why is limiting the flow of current in a circuit important? All components have Power ratings which tell us the maximum levels of current and voltage they can handle. Exceeding these levels for extended periods of time will damage the component. So, the power to components needs to be limited to avoid damaging them. But, a power supply is fixed in its value. To combat this issue you can place a resistor which will be able to limit the current to components and protect them from damage. 

Limiting the flow of current also has other applications. As we just saw that by controlling the current to a component (using a resistor) we also gain the ability to control the power it receives. This power control can be used to control the speed of a motor, adjust the brightness of a light, alter musical tone pitch, control the amplitude of an amplifier, as a few examples. 

Resistor function #2 in a circuit: Reduce voltage

The next common function that a resistor has in a circuit is Reduce voltage. A resistor is going to have a voltage drop across it. The magnitude of the voltage drop is determined by ohm’s law which is equal to the current through the resistor, multiplied by the resistance of the resistor. The greater the resistance the greater the voltage drop. 

Now when two resistors are placed in series and connected to a supply voltage (as seen below), the configuration is known as a Voltage Divider. 

This configuration gives us the ability to reduce the supply voltage to a desired value. This value is determined by the resistances of the two resistors and is calculated using the formula below.

To achieve a desired output voltage, we first set the resistance for R2. Then we rearrange the formula to calculate the resistance of R1 which will give us our desired output voltage.

For example, say we required a 4V at our output (the supply voltage is 5V). We first select the resistance of R2 (1K). We then rearrange the equation to make R1 the subject (as we just saw above), and plug in the values. This gives us a value of 250. So to get a 4V output, you will require a resistor with a resistor of 250Ω for R1. However, a note has to be made. The value of 250Ω might not be available, so you will just have to select the next best value according to the Standard Resistor Value E Series

This ability of a resistor to reduce voltage in the voltage divider configuration can be utilised as a voltage regulator to step down a voltage. reduce the input voltage to a microcontroller or bias active elements (as we shall see later). 

Resistor function #3 in a circuit: Temperature control

When current flows through a wire, electrical energy is converted to heat energy. This phenomenon was discovered by an English physicist named James Prescott. He formulated that the heat generated per second by a conductor carrying current is proportional to the conductor’s electrical resistance and the current through the conductor squared. This formula and phenomenon is known as Joule’s Law. 

Q = I² x R x T (Joule’s Law)

Q = Heat

I = Current

R = Resistance

T = Time

As you can see from the formula, heat has a directly proportional relationship with resistance. This means that by varying the resistance of a resistor we can control temperature. 

Resistor function #4 in a circuit: Fuse

As we saw earlier, all components and devices have maximum power ratings which should not be exceeded. By properly designing our circuits we can ensure that these current and voltage levels are within safe operating conditions. However, even with proper designing, circuits can still be subjected to high currents which are known as Overcurrents. Overcurrent is a situation where the current rises to levels above the normal current levels of a circuit. 

Possible causes for over currents include;

• Short circuits
• Excessive loads
• Incorrect design
• Arc fault or,
• Ground fault

Fuses are electrical safety devices that protect circuits and components from overcurrent. It consists of a thin wire that melts when excessive current (above the nominal levels) flows through it. 

A resistor has the ability to operate as a fuse. This type of resistor is known as a fusible resistor. It melts just like a fuse when excessive current flows through it, protecting the circuit and components from damage. But, the benefit of a fusible resistor is that it acts as a normal resistor under normal operating conditions.

Resistor function #5 in a circuit: Filtering, Wave-shaping, Timing

Resistors can do awesome things by themselves, but when they combine their abilities with other components they can achieve even more. The two components that are best friends with the resistor are the Capacitor and Inductor. The resistor can be combined with these components to form RC (resistor and capacitor) and RL (resistor and inductor) circuits.

Each type of circuit has its own set of unique applications which include Filtering, Waveshaping and Timing.

Resistor function #6 in a circuit: Pull-up and Pull-down resistors

Microcontrollers are very important devices in Embedded Systems. They act as the brains of these systems in charge of controlling operations, flow of information and input and outputs. Microcontrollers are digital devices with pins that can be in either two states or logic levels;  ON (HIGH) or OFF (LOW) which is represented by binary; 1 and 0 respectively. These pins can be configured either as inputs or outputs. Buttons and switches can be connected to these pins when configured as an input. However, if we just connect a button to a microcontroller, the input would be left floating (which essentially means the pin could float between the two logic states) which is an unwanted scenario. 

Resistors are used to help tie or secure an input pin to a logic level so it is not left floating. A resistor can be connected to ground (0 or LOW). This type of configuration is known as a Pull-Down Resistor and helps secure a LOW logic state. Or, it can be connected to the supply voltage (1 or HIGH). In this configuration it is known as a Pull-Up Resistor and helps secure a HIGH logic state. 

Resistor function #7 in a circuit: Bias active elements

Active elements are devices with the capability of generating electrical energy. They take an input signal, and produce a larger signal at its output. Transistors are common active elements and an important component in the world of electronics. They have two specific roles; amplify electric current or block it. 

Transistor biassing is a crucial part when working with transistors which involves setting a transistor’s operating voltage or current conditions to the right levels so as to ensure input signals are amplified correctly. Resistors are used to help bias transistors. It can be done in two ways either by using a single feedback resistor or a voltage divider configuration.

Resistor function #8 in a circuit: Terminate transmission lines

We live in the age of information. We are constantly sending and receiving information on a daily basis. One way we send information is via transmission lines. Resistors are used in transmission lines to dissipate energy in the form of heat. But, why? They are used to absorb energy to prevent reflections within the cable. In an ideal transmission line (one without a resistor), when a piece of data reaches its destination it will still have energy and reflect back and forth interfering with other data. As we know now, resistors dissipate energy in the form of heat which comes in useful in this exact application. The resistor can absorb this energy so that the data does not reflect back and forth. 

Resistor function #9 in a circuit: Heating

Last but not least for resistor functions is Heating. It has been mentioned numerous times already, but it won’t hurt mentioning it again one last time; when electrical current passes through a resistor, energy is lost in the form of heat. This heat comes from electrical energy being converted to thermal energy. Most of the time this is unwanted. The less hot a resistor gets the better. But, there are applications where this heat can be put to good use. Fan heaters, toasters, are some of the most common devices that make use of resistors for heating purposes. Other applications that make use of this include Aeronautics, Automotive, Military and Smart clothing industries.

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It helps power electrical and electronic devices in our homes, businesses, schools, streets, airports, and the list goes on and on. 

You might be reading this article on your mobile phone, or laptop, whose battery was charged using the awesome powers of electricity. 

However, electricity is no laughing matter. 

It can be highly dangerous to electrical and electronic devices that use it, as well as ourselves. 

So when it comes to electricity, we need to have contingency plans in place to protect the devices, as well as ourselves from its raw power.

This contingency plan comes in the form of something known as a Fuse. 

But, what does a fuse do in a circuit?

The fuse plays a vital role in electrical and electronic circuits. It’s main purpose is to fail under overcurrent conditions thereby interrupting the flow of this overcurrent which could damage electrical or electronic components.

This article will dive into more detail of what a fuse does in a circuit, as well as different applications where you find a fuse, what overcurrent is and why we need protection against overcurrent.  

What is a fuse

The fuse is an electrical device that is designed to fail when subject to excessive currents that are not nominal in that particular circuit (I say particular circuit because every circuit is different having its own current limit).

The image below shows what the inside of the fuse looks like;

The fuse has many different versions of symbols that appear in circuit diagrams and schematics. Below are some of the most common; 

You can see in the first diagram,at the heart of the fuse is the Fuse wire. 

This fuse wire is the star of the show,whose job is to melt in the event of overcurrent conditions (which shall be discussed in the next section).  

The *fuse wire is a thin wire* made of conductive material which has a low melting point (this melting point however, is not in the range of the nominal currents that it would be subject to). 

What is over-current?

Every electrical and electronic device will have a Power rating. 

This rating indicates the maximum values of Voltage and Current that devices must operate under to work effectively.

I say under because going over these values will cause damage to the device, circuit, and components. 

Over-current, is an unwanted scenario when current levels rise above their nominal levels. 

If the overcurrent lasts for a long time, it will damage components and circuits within the device.

There are multiple causes for overcurrents which include;

• Short circuits
• Excessive load
• Incorrect design
• Arc fault 
• Ground fault

What does a fuse do in a circuit?

So, we know the dangers that electrical and electronic circuits are subject to which are Overcurrents and that a fuse is a device designed to fail under high currents.

It’s a match made in heaven! 

So, what does a fuse do in a circuit?

Put simply, the fuse has one job in a circuit, which is to fail when subject to excessive currents such as in the scenario of overcurrents. 

Examples are a great way to understand new concepts so let’s take a look at a simple circuit and what a fuse does to protect it. 

Below is a circuit that has a lamp powered by a battery along with a fuse for protection. 

Remember every device has an electrical rating. So, let’s assume the ratings for each of the components;

• Battery (12V)
• Lamp (12V , 1A)
• Fuse (12V, 1A)

Under normal conditions the battery provides a stable current of 1 Amp which powers the lamp. 

Since this current value is within the rating range of the fuse, there is no interruption to flow of current. 

Now, let’s imagine that an overcurrent scenario occurs causing a rise in current as pictured below.

As you can see the current value has risen to 2 Amps. But, the lamp is only rated to handle a current of 1 Amp. This rise in current will damage the lamp if it persists for some time. 

Lucky for the lamp, the fuse is also rated at 1 Amp. This means that the little fuse wire inside the fuse is going to melt thereby stopping the flow of current and protecting the lamp. 

This is essentially what a fuse does in every circuit. Protect its peers from destruction! 

Fuses are generally connected in series with electrical and electronic components that they are protecting. 

Why does the fuse wire melt in over-current scenarios 00 

Wires come in a variety of sizes which are capable of carrying a certain amount of current. 

Wire gauge is a measurement system which indicates the diameter of the wire. The information present in a wire gauge indicates how much current a particular wire can carry, its resistance and its weight.

Without going into too much detail, when there is a flow of current a certain amount of heat is generated. 

You might have felt this when using your smartphone for long periods of time, or touching your computer CPU. 

The wire gauge system helps us select the right wire which is capable of handling a certain amount of current.

For example, say we have a 20 Gauge electrical wire. 

This wire is capable of carrying a maximum current of 3A according to the American Wire Gauge (AWG) system. 

When subject to a current of 3A or less, the electrons (current) can freely move along as the wire is able to cope with these many electrons.

If we bump up the current to say 4A, there are now more electrons, but the surface area of the wire has not changed. 

This means that electrons are now going to start bumping into each causing a greater build of friction. As you might know, a greater build of friction leads to a greater build of heat which can melt the wire and its insulation causing damage. 

The fuse wire works in the same principle. 

The size of the wire is chosen to handle a certain amount of current (and therefore heat). 

If it is subject to a higher current, the heat generated is going to melt the fuse wire. 

Different types of fuses available for circuits

Electrical and electronic circuits can be classed into two main categories; Alternating Current (AC) and Direct Current (AC).

Alternating Current circuits deal with a current that reverses direction multiple times a second at regular intervals. 

Direct Current has currents that flow only in one direction. 

AC circuits deal with higher voltages compared to circuits that use DC. 

Due to this, fuses are broken down further into two categories;

• AC Fuses
• DC Fuses 

DC Fuses

The main problem when it comes to DC applications for fuses, is the ARC that is produced between the gap of the fuse when the fuse wire melts.

An arc can form between the gap within the fuse due to constant DC value. 

By increasing the distance between the electrodes, we can eliminate this arcing problem. DC fuses are designed to be bigger specifically to combat this issue.

AC Fuses

In AC circuits, arcing is not much of a problem as the amplitude of voltage changes up to 60 times every second (for frequencies of 50Hz or 60Hz). 

Therefore, the distance between the electrodes can be smaller compared to DC fuses. 

Different packaging of fuses used in specific circuits

As there are many different types of electrical and electronic circuits, as well as diverse applications, so too are they a wide variety of packaging of fuses to suit each application.

Note, these fuses have different packaging styles as well as voltage ratings appropriate for each application and sit under either the DC or AC fuse umbrella.

Cartridge fuses

If you need to protect high voltage electrical appliances such as motors, refrigerators, air-conditioners etc, a Cartridge fuse is your best option. 

These types are rated for voltages up to 600V (AC), and currents up to 600A. 

Cartridge fuses are further divided up into two options;

• General purpose (no time delay)
• Heavy duty (with time delay)

High voltage fuses

High voltage fuses were designed to work with voltages ranging from 1500V to 13kV!

You will find them in power systems protecting the likes of power transformers, distribution transformers, instrument transformers etc. 

Copper, silver or tin are the go to materials used for the fuse wire in high voltage fuses. 

Automotive fuses

You might have come across this type of fuse in your car.It is a plastic body with two metal teeth. Used commonly in automobiles for wiring and short circuit protection.

The voltage range for automobile fuses is around 12V – 42V. 

Surface mount fuses

Electronic circuits have shrunk in size over the years thanks to Surface Mount Devices (or SMD for short) technology. 

Things like smartphones can fit in the palm of your hand thanks to SMD components. 

SMD fuses are fuses used to protect SMD circuits in DC applications. Circuits like computers, cameras, smartphones and much more. 

Rewire-able fuses

Rewire-able fuses are most commonly used in low voltage systems in industries or or home electrical wiring. 

It gets its name because of the fact that it can be easily rewired.

Thermal fuses

Named aptly due to the fact that this type of fuse is temperature sensitive. 

The fuse wire is composed of an alloy that melts under high temperatures. They are also commonly known as Thermal Cutouts.

Re-settable fuses

Last but not least, is the Re-settable Fuse.

This fuse can be used multiple times without having to replace the fuse cartridge. 

They operate in the same manner as other fuses by opening in the case of an overcurrent, but unlike their counterparts, they can close the circuit again, resuming normal operation. 

Resettable fuses are great for applications where going in manually to replace a fuse might not be safe to do so.

Applications and circuits where fuses are used

We are surrounded by electrical and electronic devices. 

There are devices that make our lives easier with things like washing machines, dishwashers, air-conditioners, microwaves and much more.

Or, they help to entertain us and add some spice to our lives with devices like smartphones, computers, televisions, dvd players, etc. 

We now know the damage overcurrents can cause, and these devices are at risk of being damaged without the use of a fuse. 

Rather than naming every single device that uses a fuse (which will be many), I shall list the different systems and applications;

• Power systems
  • Motors
  • Transformers
• Power distribution 
  • Homes
  • Businesses
  • Schools
• Entertainment
  • Televisions 
  • DVD players
  • Gaming consoles
• Portable electronics
  • Smartphones
  • Digital cameras
• Computing
  • Laptops
  • Printers
  • Scanners
  • Hard Disk Drives
• Home Appliances
  • Toaster
  • Washing machine
  • Dishwasher 
  • Microwave
• Automotive
  • Cars
  • Motorbikes
  • Scooter

This isn’t an exhaustive list by any means. There are many more applications. Pretty much anything that uses electricity will benefit with a fuse in its circuit to protect it. 

Is it necessary to use a fuse in a circuit?

If the circuit has a chance of being subject to overcurrents, the simple answer is yes! 

Some electronic circuits might be able to go about their lives without the need of a fuse, but in general, it’s probably a good practice to design a circuit with a fuse. 

Does the fuse affect the overall resistance of a circuit?

No, the resistance of a fuse does not affect the overall resistance of a circuit. 

Fuses are made from metal alloys that have very low resistance and melting point. 

They are manufactured so that the cross sectional area of the fuse is able to carry the rated current of the circuit it will be used in and have a low resistance so it is a miniscule part of the overall circuit, which means a very low voltage drop. 

What is the difference between a fuse and a circuit breaker?

You might have heard both these terms before. But, what is the difference between a fuse and a circuit breaker?

The main difference is the reusability. 

A fuse can only be used once. When the fuse wire within the fuse has melted, the fuse cartridge needs to be removed and replaced with a new fuse.

Whereas, a circuit breaker can be reset multiple times if it has been tripped.

But, how does a circuit breaker achieve this? 

When current levels rise above the threshold limit within a circuit breaker, rather than a wire melting, a little electromagnet inside the circuit breaker pulls the contact points apart thus stopping the flow or current. 

Selecting the right fuse for your circuit

Choosing the right fuse for a circuit depends on the voltages and currents the circuit will be subject to. Then the appropriate fuse can be chosen. 

The general rule of thumb is to choose a current rating that is 150% – 200% higher than the maximum current value that the circuit will see.

First you would calculate the maximum current the circuit would be subject to. Then select a fuse with a rating 150% – 200% higher than that value. 

Say you have a washing machine running a load. The motor running is rated at 754W and a voltage of 115V. So the current is 754 / 115 = 6.5 A at full load. 

Going with the rule of thumb, you would select a fuse around 10A.

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Whether it be a calculator to solve equations, or a gaming console to take us away from reality. 

Every electronic device contains a circuit which contains vital components that contribute to the overall functionality of that device.

A Thermistor is a component which serves a specific purpose in many different circuits.

So, what does a thermistor do in a circuit?

The main purpose of a thermistor is to give a circuit the ability to sense changes in temperature. A thermistor is a component which has the ability to change its resistance as temperature changes.  

Closer look at a thermistor

Let’s take a closer at the thermistor which will help you better understand what it actually does in a circuit.

The thermistor is essentially a resistor which has the ability to change its resistance.

This change in resistance is caused by an external change in ambient temperature. Think of it as a thermometer whose temperature is related to its resistance.

What this means is that a change in ambient temperature will cause a change in resistance. 

The word thermistor is a combination of the words ‘thermal’ and ‘resistor’. 

They are constructed using metal oxides which can be encapsulated into a bead, disk, or cylindrical form.

Below is the common circuit symbol of a thermistor;

Working principle of a thermistor

If we opened up a thermistor we would find a semiconducting material.

A semiconducting material is chosen as they have a greater resistance than conducting materials, while having a lower resistance than insulating materials. 

Choosing the right materials is crucial as this directly affects the relationship between temperature and resistance (this can be viewed better by the graph curve of Resistance vs. Temperature)

They contain metal oxide semiconductors, binders and stabilizers pressed into wafers which are then cut into a particular form depending on their packaging they will be used in. 

So, a change in ambient temperature causes a change in resistance within the semiconductor material. The key is that the initial resistance of the thermistor is known.

There are two types of thermistors, each having different working principles. However, their purpose stays the same which is to alter their resistance to changes in temperature. 

The first is known as a Positive Temperature Coefficient (PTC) thermistor. 

The resistance of a PTC thermistor increases as temperature increases and decreases as temperature decreases. 

The relationship between resistance and temperature in a PTC thermistor is directly proportional.

Negative Temperature Coefficient (NTC) thermistors have reverse functionality. 

Their resistance decreases with an increase in temperature and increase with a decrease in temperature.

 The relationship between resistance and temperature in a NTC thermistor is inversely proportional. 

Main purpose of a thermistor in a circuit

Just like how we have five senses (sight, smell, hearing, touch and taste) that help us interpret and navigate the physical world, a thermistor gives a circuit the ability to sense the physical world as well. 

It does this by allowing it to sense changes in temperature by varying its resistance. 

Because of this the thermistor is used in many applications where temperature sensing is a crucial component of the system. 

Below are some common household devices that you will be familiar with that will use a thermistor as part of their circuit;

• Fire alarms 
• Ovens
• Refrigerators 
• Heaters

Other applications of a thermistor in a circuit

While their main purpose in a circuit is to sense temperature, the working principle of a thermistor enables it to be used for other applications too.

Inrush current limiting

In every electrical and electronic circuit you have a Steady-state current which is the nominal safe value of current seen by the circuit. 

However, there are times when the current exceeds this steady-state value which can damage components of the circuit. 

This current is known as Inrush current. 

Inrush current is the maximum draw of current and occurs when the circuit is switched ‘ON’. It can last for a few cycles of the input waveform. 

A thermistor can be used in a circuit to protect it from inrush currents. 

When the circuit is off and no current is flowing, the thermistor has a high resistance. When the circuit is switched ‘ON’ the thermistor opposes the inrush current due to its high resistance. 

As the flow of current warms the thermistor, its resistance drops thus allowing the current to flow at a much steadier rate. 

Over-current protection

Thermistors can be used in circuits to protect components from Overcurrents.

Similar to inrush currents, overcurrent is an excess in current not nominal to the steady-state value which can be caused by overloading the circuit, a short circuit, a ground fault, or an arc fault. 

A motor is a component that can be regularly subject to overcurrents. 

If the motor is overloaded or its rotation has locked, an overcurrent scenario can occur causing high currents to flow through the motor.

High currents cause high temperatures which can place a thermal stress on the internal coils and windings of the motor. 

PTC thermistors are used to reduce this thermal stress. 

The overcurrents cause the thermistor to heat up which then increases its resistance thereby reducing and limiting the high currents.  

Is a thermistor the same as a thermocouple?

A Thermocouple is a device whose main purpose is the same as a thermistor, which is to measure temperature. 

However, while they both measure temperature, they go about doing it two different ways. 

A thermistor does so by varying its resistance according to temperature. 

On the other hand, the thermocouple varies its output voltage based on the connection of two dissimilar metals. 

Is a thermistor better than a thermocouple?

If both do the same thing, which is better? 

Each of them have their own advantages in different scenarios and choosing between a thermistor and thermocouple in a circuit comes down to the needs of the application. 

Below is a table of some important characteristics of both the temperature sensing devices which will help you decide which is best suited for your application. 

In general, thermistors are chosen when ruggedness, reliability and stability are of importance. This makes them great for applications and environments where conditions are extreme and electronic noise is present.

The post What does a thermistor do in a circuit? appeared first on Electronic Guidebook.

It comes in many different forms which include Mechanical, Electromechanical, and Piezoelectric.

A switch is an electronic component that has the function of allowing and preventing current flow when used in a circuit. 

But, can a buzzer function as a switch in a circuit? A buzzer cannot function as a switch in a circuit. It’s primary function is to produce an audio signal in the form of ‘buzzing’ or ‘beeping’ when a voltage is applied to it. It does not have the ability to open and close a circuit the same way a switch does.

The main function of a buzzer and switch in a circuit

There are plenty of electronic components used daily in circuits. Individually, they have a certain function in the circuit that contributes to the overall functionality of the circuit. 

A switch and buzzer are no different with each having a key function to play in a circuit. 

Understanding what each does will help you understand why a buzzer cannot function as a switch in a circuit. 

What is the main function of a switch in a circuit?

Let us first take a look at the switch. 

Below, is a simple circuit with a load connected to a battery.

In this circuit the battery is continuously supplying the load with power. 

However, at a certain point the battery is going to run out of energy and therefore will no longer be able to supply power to the load. 

Having this sort of setup in the real world is not very applicable. 

You are rarely going to need to have the battery constantly powering a load. 

This is where the switch plays a crucial role. 

An electrical/electronic switch is a component that connects or disconnects the conducting path in an electrical/electronic circuit, either allowing current to flow, or preventing it from flowing.

If we modify the diagram earlier and add a switch, we get the circuit below. The switch can be in two states ; Closed and Open. 

In diagram A, the switch is Open, causing a break in the conducting path, thereby preventing current from flowing through the LED and powering it. 

Diagram B has the switch closed which creates a conducting path and therefore allows current to flow from the battery to the LED. 

So, you can see, the main function of the switch is to either allow or prevent current from flowing in a circuit. 

What is the main function of a buzzer in a circuit?

Having the ability to produce sound in electronics has many different applications. 

The buzzer is an electronic component that has the ability to produce sound when a voltage is applied to it. 

This can be utilised in many applications. 

One of the biggest applications where a buzzer plays a crucial role is a smoke alarm. When you are sleeping your sense of smell and sight are impaired. 

If a fire starts in your home while you are sleeping, you will have no way of knowing. A buzzer provides a way of letting you know a fire has started through sound. 

Other applications include alarm clocks, doorbells, electronic musical instruments, greeting cards, security systems and many more applications. 

There are three different types of buzzers available ; Mechanical, Electromechanical, and Piezoelectric.

So, a buzzer’s main function in a circuit is to provide an audio signal. 

Why a buzzer cannot be used as a switch in a circuit

Now that you know the function of a switch and buzzer in circuit, we can discuss why a buzzer cannot function as a switch in a circuit.

The main function of a switch is to close and open a circuit, thereby allowing and preventing current to flow respectively.

While the buzzer’s main function is to produce sound when a voltage is applied to it. It is primarily an output device that functions to provide an auditory signal which can be utilised in many different applications. 

The buzzer does not have the ability to function as a switch, as it mechanically has no way of connecting and disconnecting the conducting path of a circuit the way a switch does.

What instance would a buzzer function a switch in a circuit?

There is an instance where a buzzer can disconnect the conducting path in a circuit.

This scenario could arise if the buzzer is damaged and causes an open circuit.

An open circuit  occurs when two points in a circuit are physically disconnected thus representing a switch that is ‘open’.

If a buzzer is damaged, there is a possibility that there is a break in circuit within the buzzer thereby causing an open circuit. 

However, this is far from a buzzer functioning as a switch in a circuit. You wouldn’t want to damage your buzzer just to open a circuit to make it ‘function’ like a switch.

Connecting a switch would be the more logical and sensible approach.

What other functions can a buzzer have in a circuit?

While a buzzer cannot function as a switch in a circuit, it does have another function other than just producing sound.

The piezoelectric type of buzzer has the ability to produce a voltage at its terminals when pressure is applied to the disc responsible for producing sound.

This opens a new set of possibilities for the piezoelectric buzzer. 

It can be used in applications where a sudden force or constant pressure needs to be sensed and/or measured. The piezoelectric buzzer can be connected to a microcontroller analog input which can interpret the voltages from the buzzer. 

Applications could include motion detection, door knock sensor, force measurement, pressure measurement, and many more.

What is the most basic circuit of a buzzer and how does it function

While there are many circuit configurations available for the buzzer, the most basic is one with a battery, switch, and buzzer (similar to our circuit at the beginning).

When the switch is closed, the battery energises the coil within the buzzer causing a rapid back and forth movement of a contact inside the buzzer causing a loud buzzing sound.

Opening the switch causes the coil to be de-energised which in turn will stop the buzzer from producing sound. 

The piezoelectric buzzer requires a bit more than just voltage. It requires some sort of oscillator that is capable of producing a sinusoidal type wave. Just connecting it to a DC voltage will cause a click and no buzzing sound. 

A microcontroller can be used to drive a piezoelectric type buzzer.

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