People who are quite used to reading resistor colour codes will generally be able to glance at the body and tell you within two seconds what the value of that resistor is, without the use of any conversion tables. Believe it or not, but you too will take this as second nature after some experience.
To prevent having to write or work with a large number of figures, certain conventions are applied to how resistor values are written once they reach various quantities.
As a couple of examples; a 4, Ohm resistor would be written as either 4. Just for completeness, values below 10 Ohms can also be written in this way; 3. There is no hard and fast rule governing which abbreviated method of writing them is used. Originally they were written with the decimal point in the middle, but when circuit diagrams started to appear on-mass, particularly in hobby magazines, it became apparent that due to the printing techniques and low-grade paper used, the decimal point was very often not being reproduced very faithfully.
This lead to misinterpretation of the printed values and constructors building circuits that didn't work. And the problem wasn't restricted to hobby magazines either, a lot of commercial circuits and technical manuals also suffered the same omissions.
Because of this, a lot of circuits started to be produced which had resistor values written using the letter in the middle method. Another character also used to represent resistance was the Omega sign itself - , but this has now largely been replaced by the capital letter "R". Because circuit diagrams were originally drawn out on paper by draftsmen using stencils containing the various electronic symbols and characters. With the advent of widely available CAD machines to generate circuit diagrams, and wordprocessors to type the written documentation, they suddenly realised that the Omega symbol was not a standard typographical character.
All of the colours must be converted to their assigned values in order to calculate the resistance, and the result is always produced in Ohms.
This is because column one will never contain black, and column three will never have a colour with an assigned value above 6, since basic resistor values range from 1 Ohm - brown, black, gold, to 10 Megohms - brown, black, blue. Using our 27K example, the resistance is calculated as follows;. Next, the multiplier band indicates how many zero's to write down after the first two digits, and here we need three of them - "". That's it! You now have the resistance value, in Ohms, of that resistor - 27, Ohms.
Since every 1, Ohms represents a Kilohm or "1K", the value in the example works out to be 27K. However, only values from 10 Ohms upwards can be represented with the "usual" colour range from black to white, since the minimum valid colour sequence is Brown, Black, Black - 10 Ohms.
The figure on the right shows how values below 10 Ohms are represented. Here, gold or silver are used for the multiplier band, only now this means the calculated resistance value must be DIVIDED by 10 or respectively. In our example a 5. If the multiplier band was silver, this value would be 0. However, it is very unlikely nowadays that you will find these types of resistors with a silver multiplier band.
This means the actual resistance could be as low as 25, Ohms, or as high as 28, Ohms. A gold tolerance band is possibly the most common you will find on standard carbon film resistors. But it is still part of the colour code standard, so it has been included with the rest of them.
As with the 4 band types, all of the colours must be converted to their assigned values to calculate the resistance, and again the result is always produced in Ohms. If we know the current running through a resistor, we can calculate the power as:. Resistors are paired together all the time in electronics, usually in either a series or parallel circuit.
When resistors are combined in series or parallel, they create a total resistance , which can be calculated using one of two equations. Knowing how resistor values combine comes in handy if you need to create a specific resistor value. N resistors in series. The total resistance is the sum of all series resistors. So, for example, if you just have to have a Finding the resistance of resistors in parallel isn't quite so easy.
The total resistance of N resistors in parallel is the inverse of the sum of all inverse resistances. This equation might make more sense than that last sentence:. N resistors in parallel. To find the total resistance, invert each resistance value, add them up, and then invert that. The inverse of resistance is actually called conductance , so put more succinctly: the conductance of parallel resistors is the sum of each of their conductances.
As a special case of this equation: if you have just two resistors in parallel, their total resistance can be calculated with this slightly-less-inverted equation:. 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. Active Oldest Votes. Hope this helps. Hutner Hutner 66 3 3 bronze badges. I have visually no clue how to distinguish them, only with my multi-meter.
Here is a good visual reference. Anyway, my comment is more about the orientation of the resistor. Just like OPs question.
In my case I had the 2 mentioned resistors next to each other, they looked identical, no extra separation between the multiplier ring and the tolerance ring. Add a comment. Robert Fay Robert Fay 1, 3 3 silver badges 12 12 bronze badges. Juan Juan 6 6 silver badges 18 18 bronze badges. I would have to desolder one side of the resister to measure it. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. While most semiconductor resistors are embedded well within integrated circuits and an end user does not "put them in" backwards or any other way, a designer could certainly 'drop them in' incorrectly during layout if they are opening up circuit libraries or possibly turning off design rule enforcement , and if bulk semiconductor resistors as opposed to thin film silicon resistors ever did appear as discrete devices it may indeed matter electrically in some way how they are inserted.
So while the question gives the impression we are inserting a carbon resistor into a circuit with the gold band on the left vs on the right, the actual thing which we call a resistor may be quite different in different situations. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Learn more. Can i put a resistor in backwards? Asked 5 years, 6 months ago.
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