When do you use a resistor in a circuit

As an even more special case of that equation, if you have two parallel resistors of equal value the total resistance is half of their value. A shorthand way of saying two resistors are in parallel is by using the parallel operator:.

For example, if R 1 is in parallel with R 2 , the conceptual equation could be written as R 1 R 2. Much cleaner, and hides all those nasty fractions! As a special introduction to calculating total resistances, electronics teachers just love to subject their students to finding that of crazy, convoluted resistor networks.

A tame resistor network question might be something like: "what's the resistance from terminals A to B in this circuit? To solve such a problem, start at the back-end of the circuit and simplify towards the two terminals.

In this case R 7 , R 8 and R 9 are all in series and can be added together. Making our circuit:. Now the four right-most resistors can be simplified even further. R 4 , R 5 and our conglomeration of R 6 - R 9 are all in series and can be added. Then those series resistors are all in parallel with R 3. And that's just three series resistors between the A and B terminals. Add 'em on up! Resistors exist in just about every electronic circuit ever. Here are a few examples of circuits, which heavily depend on our resistor friends.

Resistors are key in making sure LEDs don't blow up when power is applied. By connecting a resistor in series with an LED, current flowing through the two components can be limited to a safe value. When sizing out a current-limiting resistor, look for two characteristic values of the LED: the typical forward voltage , and the maximum forward current. The typical forward voltage is the voltage which is required to make an LED light up, and it varies usually somewhere between 1.

The maximum forward current is usually around 20mA for basic LEDs; continuous current through the LED should always be equal to or less than that current rating. Once you've gotten ahold of those two values, you can size up a current-limiting resistor with this equation:. V S is the source voltage -- usually a battery or power supply voltage. For example, assume you have a 9V battery to power an LED. If your LED is red, it might have a forward voltage around 1. A voltage divider is a resistor circuit which turns a large voltage into a smaller one.

Using just two resistors in series, an output voltage can be created that's a fraction of the input voltage. Two resistors, R 1 and R 2 , are connected in series and a voltage source V in is connected across them. The voltage from V out to GND can be calculated as:. For example, if R 1 was 1. Voltage dividers are very handy for reading resistive sensors, like photocells , flex sensors , and force-sensitive resistors. One half of the voltage divider is the sensor, and the part is a static resistor.

The output voltage between the two components is connected to an analog-to-digital converter on a microcontroller MCU to read the sensor's value. Here a resistor R 1 and a photocell create a voltage divider to create a variable voltage output. A pull-up resistor is used when you need to bias a microcontroller's input pin to a known state. One end of the resistor is connected to the MCU's pin, and the other end is connected to a high voltage usually 5V or 3.

Without a pull-up resistor, inputs on the MCU could be left floating. There's no guarantee that a floating pin is either high 5V or low 0V. Pull-up resistors are often used when interfacing with a button or switch input. The pull-up resistor can bias the input-pin when the switch is open.

And it will protect the circuit from a short when the switch is closed. In the circuit above, when the switch is open the MCU's input pin is connected through the resistor to 5V. When the switch closes, the input pin is connected directly to GND. The value of a pull-up resistor doesn't usually need to be anything specific. But it should be high enough that not too much power is lost if 5V or so is applied across it.

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Resistors certainly aren't the only basic component we use in electronics, there's also:. See our Engineering Essentials page for a full list of cornerstone topics surrounding electrical engineering. Take me there! Need Help? Connect and share knowledge within a single location that is structured and easy to search. I have been trying to find answers on Google to this question but cannot seem to find any answers that actually pertain to what I am wanting to know. I would consider myself a beginner in the area of electronics having some experience but not understanding how everything comes together outside of the some of the basics.

What I am wondering is this; How can I tell if I need to use a resistor in a circuit? More specifically, When I am hooking sensors up to an Arduino, how can I determine if I need resistors in the circuit? Thanks in advance. From the specifications of the sensor, you know the maximum current the sensor should be allowed to draw. Suppose you need to put 5v across the sensor. You need to know the value of a resistor to put in series with the sensor to limit the current to that maximum value or less.

So solve Ohms law for resistance R of voltage E :. That gives you the values of a series resistor to limit the current to the maximum, assuming the sensor has no or very little internal resistance of its own.

Or let's look at an LED, where the spec sheet gives you both the maximum current and the internal voltage drop called "forward voltage". Red LEDs typically have 2v forward voltage and 15 milliamps max current but don't build for "typical" parts - build for the part you have.

We'll assume a 5v power supply:. If you calculate the voltage again, using Ohm's law across the or whatever you used Ohm resistor, you'll find a voltage drop of about 3v, and adding the LED's forward voltage of 2V, you'll get the power-supply voltage of 5v.

It's about the behavior of the component or module itself, and that needs a datasheet for the component and spec-sheet for the module. An LED has a forward voltage drop but otherwise looks like a nearly short circuit, so it requires a resistor to protect it from over-current. A module often provides some circuitry around the component to help the user integrate into their project.

Of course, how much help it provide is up to the designer. One module may offer nothing more then breadboard-compatible pins where another one - for the same device - may have power-conditioning or power supply components, 3.

Why does this component need a resistor and another one doesn't? In Timing Circuits: The timing components used in timer and oscillator circuits always incorporate a resistor and a capacitor.

Here the time taken to charge or discharge a capacitor constitutes the basic time pulse or trigger for the circuit. A resistor is effectively used to control this charging and discharging process and its value is varied to obtain different time intervals. Surge Protection: The initial switch ON of a power supply may at times inflict a dangerous voltage surge into an electronic circuit, damaging its critical components.

A resistor when introduced in series with the supply terminals of the circuit helps in checking the sudden rise in voltage and averting possible harm. These resistors are generally of low values so that the overall performance of the circuit is not affected.

The above basic examples must have provided you sufficient knowledge regarding the use of resistors in electronic circuits and helped you to understand what is the function of a resistor. For further information, feel free to add your comments comments need moderation and may take time to appear.

Q1: How many types of resistors are there based on the type of materials used? A: There are many kinds of resistors based on the type of material used to make the resistor: 1. Wirewound WW Resistors 2. Metal Film Resistors 3. A resistor controls the flow of the electrical current within a circuit. Resistors are made from materials like copper or carbon, which make it difficult for the electrical charges to flow through a circuit. The most common type of resistor is a carbon resistor, which is a general purpose resistor, best suited for lower-powered circuits.

Some other common resistor types include the film resistor and the wire-wound resistor. Resistors are essential to many electoral circuits, and they can be applied to a myriad of different applications. Protect against voltage spikes. Resistors also protect components against voltage spikes. Components that are sensitive to a high electrical current, like LED lights, will be damaged if there is not a resistor to control the flow of the electrical current.

In addition, fuses and circuit breakers can also be used to protect your electrical circuit against voltage spikes. Provide the proper voltage.