Everything You Need to Know About Variable Resistor

As you may know, Resistors are omnipresent in electronic equipment and are common elements of electrical networks and electronic circuits. Variable resistors are resistors with variable resistance values. Changing the values of currents and voltages in various electrical circuits is occasionally necessary. For example, changing the volume of sound and brightness on television, the volume of sound and tone on a radio, and regulating the speed of a fan are all everyday tasks. Variable resistors can be used to make such modifications. The variable resistor function will get discussed in this article.

What Is A Variable Resistor?

Variable resistors are electromechanical transducers that work by sliding a contact (wiper) across a resistive element. The electric resistance value of a variable resistor can be modified as current across the circuit drops when the resistance in the variable resistor rises, and vice versa. They can also be used to regulate the voltage across circuit devices. As a result, these resistors are helpful in applications that require current or voltage regulation.

A potentiometer is a three-terminal variable resistor used as a potential divider. It’s termed a rheostat when only two terminals are employed. Variable resistors that are controlled electrically rather than mechanically are available. Digital potentiometers refer to these resistors.

Variable Resistor Characteristics

The relationship between the mechanical location of the moving terminal and the resistance ratio is an essential characteristic of a variable resistor. The taper is marked on the resistor. There are usually two types of taper marked: linear and logarithmic taper. The resistance ratio will be directly proportional to the mechanical position, indicating that the relationship between the two is linear. This will appear as a straight line with a constant slope on a graph.

The logarithmic taper is the other form of taper. When represented in a graph, the relationship between mechanical position and resistance ratio is logarithmic. Audio control is the most common application for resistors with this taper type.

Another critical feature of a variable resistor is knowing before selecting a resistor for a particular application. The resistor’s resolution is what it’s called. The resolution is the smallest value of resistance through which a variable resistor varies. A variable resistor with a resolution of 0.005 ohms indicates that the resistance can change by as little as 0.005 ohms. A variable resistor’s high resolution is a desirable feature.

Types of Variable Resistors

Potentiometer

The most common variable resistor is the potentiometer. It works as a resistive divider and is commonly used to generate a voltage signal based on the potentiometer’s location. This signal can be utilized for various purposes, including amplifier gain control (audio volume), distance or angle measurement, circuit tuning, etc. Trimmer potentiometers, often known as trimpots, tune or calibrate a circuit or application using variable resistors. Small potentiometers on the circuit board that can be modified with a screwdriver are common.

Rheostat

Rheostats are constructed similarly to potentiometers; however, they are utilized as a variable resistance rather than a potential divider. Instead of the three terminals that potentiometers have, they only have two. One connection is made at the resistive element’s end, while the other is made at the variable resistor’s wiper. Rheostats were once employed in series with a load, such as a light bulb, as a power control device. Rheostats are no longer often used for power control since they are inefficient. Rheostats have been replaced by more efficient switching electronics for power control. Note that preset variable resistors wired as rheostats are utilized in circuits to achieve tuning or calibration.

Digital Resistor

A digital variable resistor is a type of variable resistor in which the resistance is changed by electronic impulses rather than a mechanical movement. They can modify resistance in discrete stages and are frequently controlled by digital protocols such as I2C or simple up/down signals.

Photoresistors

A frequent type of variable resistor is photoresistors, also known as light-dependent resistors (LDRs). The photoelectric effect causes their resistance to alter the intensity of incoming light; in circumstances where the intensity of the light changes, photoresistors may be preferable.

Force Sensitive Resistor

As the name suggests, a force-sensitive resistor’s resistance varies with the applied force level. They’re commonly employed in robotic applications, such as inside a robot’s grippers.

Thermistors

A thermistor’s resistance changes as the temperature rises; negative temperature coefficient (NTC) and positive temperature coefficient (PTC) thermistors are the two types of thermistors. PTC thermistors have a directly proportional resistance to temperature, but NTC thermistors have a resistance that is inversely proportional to temperature. Thermistors are favored in various industrial applications where temperature variation sensing is crucial.

Humistors

The resistance of the Humistors changes in response to changes in humidity, as the name implies. Many internets of things (IOT) devices employ Humistors to detect environmental changes.

Variable Resistor Function

A variable resistor has a resistance channel that is provided by a track. Both ends of the track are linked to the device’s two terminals. The third terminal is attached to a wiper that controls the track’s movement. The resistance can be increased or decreased by moving the wiper through the track.

The track is usually made of a ceramic-metal mix, but it can also be made of carbon. Carbon Film Type Variable Resistors are commonly employed because a resistive substance is required. Radio receiver circuits, audio amplifier circuits, and television receivers all use them. For low-resistance applications, the resistance track could be a coil of wire. Both rotary and straight versions of the tune are available. A switch may be included in some rotary tracks. The variable resistor switch will feature an operating shaft that can be readily moved in the axial direction, with one of its ends moving from the switch’s body.

There are two uses for the rotary track resistor. One option is to alter the resistance. The switch mechanism makes electric contacts and non-contacts by turning the switch on and off. For equipment control, switch mechanism variable resistors with an annular cross-section are utilized.

Additionally, components are added to this variable resistor to make it compatible with complex electrical circuits. A focused pack is an example of a high-voltage variable resistor. This gadget can generate both a variable focus voltage and a screen voltage. It is also connected to a variable resistance circuit and a fixed resistance circuit to alter the applied voltage. Both the fixed and variable resistors are connected in series to achieve this.

Before we get into the specifics of the variable resistor function, it’s important to note that variable resistors come in various shapes and sizes, each of which performs differently. The location of a potentiometer, for example, is used to generate a voltage signal. This signal can be utilized for various purposes, including amplifier gain control (Volume control), distance or angle measurement, circuit tuning, etc. In circuits, rheostats are used to tune or calibrate items like a lamp’s brightness or the rate at which a capacitor is charged.

The most typical variable resistor use fine-tunes a voltage divider or a variable resistor sensor, such as a photoresistor, thermistor, or other variable resistor sensors. You create a voltage divider with a standard resistor and a variable resistor. Suppose you wish to utilize the voltage drop across the bottom resistor as a reference voltage. In that case, you’ll need to use a potentiometer to dial in the exact value you want to use as a reference.

Using a sensor-type variable resistor can build up a voltage divider. When the voltage drop across the sensor reaches a specific point, a second circuit, frequently an op-amp comparator, is enabled to do something else.

Variable Resistors Application

Variable resistors are used in a variety of everyday applications. Variable resistors, some of which we use daily, are all around us. Here are some instances of practical applications.

The Radio

Variable resistors can be found in your car’s radio or boombox, at home, or on your shoulder. There’s a variable resistor working beneath those volume knobs that you can’t see. The radio controls how many volts are outputted to your speakers because it is the control center for your sound system. The more volts you feed your speakers, the louder they become, and the fewer volts you provide them, the quieter they become.

The Light Dimmer

A light dimmer is another example of how variable resistors are used. In most homes, light dimmers can be found. A light dimmer’s purpose is to adjust the brightness of the lamps connected to the circuit. The dimmer accomplishes this by regulating the number of volts and, more precisely, the wattage delivered to the lamps. The bulbs will become brighter when more volts are permitted to enter them, and vice versa.

Fan Speed Controller

We’re all familiar with the revolving knob that controls the fan speed. The rotating knob is a potentiometer, adjusting the resistance as it rotates.

Lightning bulb

Resistors are used in the electronics circuits of CFL, LED, and other illumination lights.

Street lighting (LDR)

LDR is used in the automatic street lighting system (light-dependent resistors). A photoresistor is a variable resistance device whose resistance varies depending on the amount of light. The resistance of lamps is adjusted during daylight to switch off the lights. The resistance fluctuates as the sun sets, and this variation in resistance is used to switch on the lights.

Frequently Asked Questions (FAQs) About Variable Resistors

What Is A Variable Resistor Do?

A variable resistor gives the user more control over the resistance since it allows for variance or changing the resistor to fit the user’s resistance needs. As a user, changing the resistance is quite simple.

What’s the difference between a potentiometer and a variable resistor?

The resistance of the track in the potentiometer remains constant as the wiper moves, and only the potential on the wiper varies. The resistance of the track seems to change as the wiper travels and short circuits more or less of the track resistance in a variable resistor.

What Is the Advantage of a Variable Resistor?

Variable resistors offer the advantage of giving you more control over the voltage. You can also change the voltage that flows across a circuit.

What Is the Symbol of a Variable Resistor?

A variable resistor, also known as an adjustable resistor, has two terminals, one of which is a sliding or movable contact, sometimes referred to as a wiper. As shown below, a rectangular box with an arrow across is the IEC symbol for a variable resistor.

Is LDR A Variable Resistor?

An LDR is a component with a (variable) resistance that varies depending on the amount of light it receives. They can now be employed in light sensor circuits due to this.

Do Variable Resistors Have Polarity?

The polarity of a circuit does not affect resistors. As a result, there’s no need to be concerned about putting them backward. A resistor allows the current to flow in both directions equally.

Why Is A Variable Resistor Needed in A Circuit?

Simply put, a variable resistor’s electrical resistance can get changed. When working with electrical circuitry, these devices control voltage or currents. They work with the voltage and currents that are present in the circuit.

Variable Resistor Advantages and Disadvantages

Variable resistors offer the advantage of giving you more control over the voltage. You can also change the voltage that flows across a circuit.

Variable resistors have the disadvantage of needing them in specific places, which means you’ll need extra parts if you wish to divide the circuit into distinct sections. Variable resistors also don’t work in environments with a lot of vibration.

Conclusion

The resistor is the most common electronic component and one of the essential parts of an electric circuit. These resistors come in a wide range of sizes and can be utilized in various applications. According to the sort of resistance value they provide, resistors are divided into two categories: fixed and variable resistors. So there you have it: a thorough explanation of the variable resistor function and its characteristics.

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