Questions tagged [resistors]

A resistor obeys Ohm's law (V=IR); the current through it is equal to the voltage across it divided by the resistance (equivalently \$I=\frac{V}{R}\$)

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153 votes
6 answers
106k views

Why exactly can't a single resistor be used for many parallel LEDs?

Why can't you use a single resistor for a number of LEDs in parallel instead of one each?
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34 votes
5 answers
444k views

how to reduce DC voltage using resistors?

How would one go about using a 12 V DC power source to power something which needs 4.5 V DC using resistors? Is there a way to determine how much adding a resistor would drop the voltage?
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21 votes
4 answers
47k views

What does a resistor do?

OK, very basic question here. I read lots of books, searched quite a bit, and every description I read seemed to talk about the flow of electrons and right away go too deep in theory for me to grasp ...
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  • 543
106 votes
3 answers
99k views

How do I calculate the required value for a pull-up resistor?

There are many tutorials that use a pull-up or pull-down resistor in conjunction with a switch to avoid a floating ground, e.g. http://www.arduino.cc/en/Tutorial/button Many of these projects use ...
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92 votes
11 answers
163k views

Is there a correct resistance value for I2C pull-up resistors?

The datasheet of the 24LC256 EEPROM states that: The SDA bus requires a pull-up resistor to VCC (typical 10 kΩ for 100 kHz, 2 kΩ for 400 kHz and 1 MHz). I thought that any resistor with a kΩ value ...
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  • 1,402
110 votes
9 answers
110k views

Why does a resistor need to be on the anode of an LED?

Please be kind, I am an electronics nub. This is in reference to getting an LED to emit photons. From what I read (Getting Started in Electronics - Forrest Mims III and Make: Electronics) electrons ...
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  • 1,203
31 votes
6 answers
261k views

Reducing voltage with resistors

I have been looking around for an easy way to convert 12V to 5V. I have seen some people saying that a simple resistor is all that is needed. $$ Volts = Ohms \cdot Amps $$ $$ Amps = \frac{Volts}{...
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61 votes
5 answers
97k views

How to choose value of resistor in voltage divider?

I understand that the output voltage is determined by the ratio between the two resistor values, and that if the both resistors are same then output voltage will be exactly same for all; but what's ...
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  • 1,619
53 votes
2 answers
68k views

Calculating the pulldown resistance for a given MOSFET's gate

I searched and read many similar questions, but did not find a specific answer for how to calculate the correct value for a pulldown resistor for a MOSFET's floating gate. It seems like everyone ...
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41 votes
3 answers
104k views

Question about MOSFET gate resistor

I have N-MOSFET gate connected to a 4043 logic. Id is about 100mA. Both the 4043 and MOSFET have +5V. I plan to use a 2N7000. How large a gate resistor do I need between the 4043 and MOSFET. The ...
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  • 413
3 votes
5 answers
50k views

Calculating resistor value and power rating to drive an LED

I have seen many resistances with difference wattage i.e 1/4W, 1/2 W, 1 W, 2 W ,3W etc. If I have 3 W load which is a large 3W LED in my case, what resistance should I use? The LED I am using needs 3....
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42 votes
8 answers
66k views

What is a pull up and pull down?

Can some one explain this terminology please I think I understand it but not completely sure. I think pull down is where you place a resistor between +V and the other component and pull up is where ...
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  • 8,358
55 votes
7 answers
63k views

What is the usage of Zero Ohm & MiliOhm Resistor?

I am new to PCB design and I noticed that some schematics use 0Ω or 100mΩ resistors. What is their purpose and why do we need to use them in our PCB design? Normally if we wish to probe how much ...
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  • 1,381
13 votes
2 answers
3k views

How does the current limiting resistor for an LED affect current and voltage drops?

I'm having a bit of trouble understanding currrent limiting resistors in simple LED circuits. I know that I can determine the optimal resistor like so: \$\displaystyle R=\frac{V_{s}-V_{f}}{I_{f}}\$ ...
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  • 255
6 votes
3 answers
11k views

Structure of a usb 2.0 connector [duplicate]

What is the role of the outer metal connector? (the one with two square holes) Does it have a potential? Is it insulated from the 4 pins? Are the 4 pins insulated from each other?
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50 votes
9 answers
40k views

Is a current-limiting resistor required for LEDs if the forward voltage and supply voltage are equal?

For blue LEDs with a forward voltage of 3.3 V and supply voltage of 3.3 V, is a series resistor still needed to limit current? Ohm's Law in this case says 0 Ω, but is this correct in practice? ...
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  • 1,566
13 votes
7 answers
15k views

6 LEDs in parallel with a single resistor to simplify soldering

I'm trying to wire up 6 RGB LEDs in parallel, all controlled from a single source (well, three sources, one for each colour). The LEDs came supplied with resistors to limit the current of 270 Ohm for ...
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  • 377
19 votes
1 answer
2k views

Does anyone remember this article about the Euclidean Algorithm?

In the 70's I had a stack of old Amateur Radio magazines (50s-60s), and for a long time I saved an article about using the Euclidian Algorithm to combine a number of resistors to achieve a specific ...
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  • 301
12 votes
6 answers
37k views

Need help calculating resistance for transistor base

I have 3 12VDC/40A automotive relays (datasheet) that I want to use with my Arduino. Based on the tutorial I am following (link) I need transistor, resistor, and diode. I am not an electrical engineer ...
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  • 443
16 votes
3 answers
4k views

How do you determine the effective resistance of a finite grid of resistors?

Disclaimer: I am a geophysicist with limited electrical engineering background. I am not sure if this problem is incredibly easy, incredibly complex, or completely nonsensical. My goal: Determine the ...
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29 votes
5 answers
41k views

What is a "100R" resistor?

Sometimes I see references to "R" resistors. For example: Obviously the 100 refers to 100 Ohms. What does 100R mean?
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-5 votes
5 answers
27k views

How to find the resistor value using the color codes?

The title says it.
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  • 469
3 votes
1 answer
629 views

Identifying a resistor with a weird band combination

I am currently in the process of trying to repair a power supply that has had one of its DC rails fail. A resistor in the PSU has exploded and I am trying to find what value it is. Band 1: White Band ...
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  • 31
8 votes
4 answers
21k views

Detect car +12V using Arduino

I am looking to detect 12+V from a car wire using an Arduino. I have found the following schematic: I know how crazy automotive voltage can get so I just want to make sure the schematic I found ...
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  • 645
1 vote
3 answers
2k views

Understanding this AC coupled circuit

I'm having a little trouble understanding this circuit and could use some help. So far I understand that this is an AC coupled circuit, and the capacitor is a blocking capacitor. I also know that ...
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  • 195
0 votes
2 answers
4k views

Why is the voltage of a capacitor equal to the voltage of a battery connected it?

I am confused by this question. If we connect a resistor in series to capacitor then the voltage will drop across the resistor and now voltage across the capacitor is less than the source, then why ...
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55 votes
6 answers
131k views

Do I really need resistors when controlling LEDs with Arduino?

I'm just trying out Arduino Uno for the first time with 2 blinking LEDs on a breadboard. All the tutorials on the Internet seem to use a resistor. I do know the function of resistors, but does it ...
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  • 871
19 votes
6 answers
26k views

Pull Down Resistors

In my quest to understand electrical engineering, I have stumbled across this tutorial: http://www.ladyada.net/learn/arduino/lesson5.html I have understood the diagrams until I got to switches. I am ...
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8 votes
2 answers
2k views

What is the use for non-inverting input resistance in a negative feedback opamp?

Here in the Figure R5=50K. This resistor value is not in the equations to obtain output voltage, and in many tutorials non-inverting input is directly grounded without a resistor. What might be the ...
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  • 11.4k
38 votes
2 answers
84k views

Purpose of the diode and capacitor in this motor circuit

I'm hooking up a small DC motor to an arduino using an NPN transistor using the following diagrams I found online: The circuit works, and I'm successfully able to make the motor run. Now, I'm ...
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  • 757
19 votes
5 answers
67k views

accounting for LED resistance

I'm doing a simple lab (I'm a hobby EE) to reinforce my ohm's law math and learn a little about how to do proper measurements with a multimeter. I have simple circuit with a 2.2k ohm resistor ...
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  • 205
7 votes
1 answer
4k views

Basic rules to calculate the equivalent resistance of a resistor circuit

I have a certain circuit only containing resistors of different values. There is one 'input' and one 'output' for the current. How do I calculate the equivalent resistance of the circuit? Are there ...
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3 votes
4 answers
5k views

Does the resistor have to be before or after the component [duplicate]

I am an electronics beginner and I created a small little circuit, just a battery a resistor and a led, then to ground. This is the circuit: simulate this circuit – Schematic created using ...
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2 votes
3 answers
799 views

Help understanding how op amps work

I've just been introduced to op-amps and am having a little trouble understanding exactly how they work. Take this circuit, for example. Suppose that there's a 1V source here. Without the op amp ...
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0 votes
5 answers
380 views

Why does an LED always need a resistor? [duplicate]

At school I was told "Never use a LED without a resistor (before or after the LED)!". Why is that? If I have a 2V LED why can't I simply use a 2V power supply? Why should I choose a 3V (for example)...
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  • 541
97 votes
29 answers
102k views

What's the best way to store and categorise resistors/capacitors/ICs/etc?

I did a big cleanup of my collection of parts today and I now have a big pile of parts on my desk (the majority of which is resistors). My previous method of finding the resistor value I wanted was to ...
36 votes
9 answers
25k views

Organizing electronic parts? [closed]

I've got one of these cabinets, which I intend to use for storing electronic components: It has 24 drawers (each 175 x 69 x 37mm). Every drawer can be subdivided into up to six compartments by ...
40 votes
8 answers
72k views

Why put a resistor in series with signal line?

A lot of times in circuits I see a resistor placed in series in a signal line and sometimes even in series with an MCU's VDD line. Is the intention of this to smooth out noise in the line? How is this ...
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  • 3,675
26 votes
1 answer
1k views

Why are the E-series numbers different from the powers of 10?

The E-series numbers are the common values used in resistors. For example, the E6 values are: 1.0 1.5 2.2 3.3 4.7 6.8 As you can see, each is about \$10^\frac16\$ apart. But I wonder why they aren'...
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  • 361
30 votes
7 answers
31k views

How do I calculate the power rating for zero-ohm resistors?

Based on my earlier question, since there supposed to be zero voltage (V=IR) drop across a 0 Ω resistor, how do we select the power rating of such a component? For example, let's say I were to ...
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  • 1,381
20 votes
5 answers
38k views

5 Band resistors and correct orientation

few days ago i bought few (about 500) resistors and i noticed that they have 5 color bands instead of 4. My question is how do i count them (which color is the tollerence) and how should i put them? ...
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3 votes
2 answers
9k views

What does "5k1" in the given schematic mean? [duplicate]

What does the "5k1" stands for it is a normal 5k Ohm resistor? (Marked with "A" in the picture) The chip is an MAX13020 LIN-transceiver.
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  • 628
3 votes
1 answer
4k views

Resistor value labeling, what does the second number refer to? [duplicate]

Possible Duplicate: µ in the Middle of a Capacitor Rating What does 3V3 or 1V8 mean I have been looking over some schematics for an industrial Laser. Some resistors which have low values, ...
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2 votes
1 answer
2k views

What does 0.025R or 30R mean here?

On a schematic I have, some resistors read as R16, 0.025R, 3W. Some read as R60, 33R. I guessed that R16 or R60 are the labels, and 3W is the power. But what does 0.025R or 30R mean? Google search did ...
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  • 177
36 votes
5 answers
38k views

What makes a pull-up/down resistor strong or weak?

A "strong" pull (up/down) resistor would be one of a relatively low value, while a "weak" one would be of a relatively high value. For example, a pull-down resistor would be used to keep an I/O pin ...
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  • 27.9k
38 votes
6 answers
13k views

Why do resistors still use color coding?

I always wondered why color coding is still used on resistors in 2014. Here is Wikipedia's word on the original reason why : Colorbands were commonly used (especially on resistors) because they ...
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  • 543
36 votes
8 answers
9k views

Are two (or N) resistors in series more precise than one big resistor?

Let's say I have one 2 kΩ resistor with 5% tolerance. If I replace it with two 1 kΩ resistors with 5% tolerance, will resulting tolerance go up, down, or remain unchanged? I'm bad with ...
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  • 675
18 votes
5 answers
14k views

Op-Amp Input Resistor?

I'm reading through the datasheet for the TL064, which contains this figure on page 16: This is of course an instrumentation amplifier that apparently uses an inverting amplifier's output instead of ...
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  • 1,367
12 votes
2 answers
12k views

Getting higher power output by using more resistors

Is there anyway I can connect resistors to allow them to take more power such as using 4 1/4 watt resistors to get a 1 watt resistors. Or do i just have to use 1 1 Watt resistor.
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  • 8,358
4 votes
1 answer
10k views

Calculationg base-resistor between microcontroller and transistor

I'm curious, when connecting my 2N2222 transistor's base to a PWM output pin on my Arduino, I know the Arduino can deliver a maximum of 40mA current. The 2N2222 only requires around 5 to 10 mA on it's ...
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