Tagged Questions

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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0
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2answers
22 views

What are the mechanisms at work in a pull-up or pull-down resistor circuits with a push-buttons and a GPIO?

I have a question regarding the GPIO (from a Arduino board for example). How does it work exactly when you use it as an input pin? What are the mechanisms at work when you use it in a pull-up and ...
2
votes
4answers
150 views

Find the resistor's value

I have bought some resistors and I am trying to find their value. The thing is that in class they taught us that you use the gold strip to find which is the right side at first and then you check the ...
0
votes
1answer
56 views

How to solve this circuit using mesh analysis?

simulate this circuit – Schematic created using CircuitLab How would I solve ...
1
vote
3answers
130 views

May I power atmega32a-pu microcontroller from AA batteries?

I need to provide +-4.5V to the microcontroller. That would be fine by having 4x rechargable batteries, but how is it with current? On each AA battery is written min.2550mAh. I am not sure but I think ...
2
votes
4answers
417 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 go too right away deep in theory for me to grasp ...
8
votes
3answers
1k views

LED strips: 46% resistive losses?

I recently bought these LED strips. They are supposed to run on 12V/72W and have 300 x the SMD 5050 LEDs on it. Schematic: simulate this circuit – Schematic created using CircuitLab The ...
0
votes
0answers
36 views

24V dc motor problem [on hold]

I am a owner of an logitech g27 wheel and having some trouble with it. The problem is that the motors getting very hot to the point where you can't even touch them (since i'm out of warranty i took ...
0
votes
0answers
30 views

PNP collector voltage drop under fan load?

Im trying to build a circuit to drive a fan. Im following an example that i found online. R5 is a 10k thermistor R6 represents the fan to drive (starting resistance 70k). Its a 12v pc fan but it will ...
1
vote
3answers
129 views

What is the drawback of a high-value resistor for positive comparator feedback / hysteresis?

I'm building a simple circuit which has an LM211 comparator at its heart. The positive input is connected to a 10k-10k resistor divider across the supplies, stabilized by a 1uF capacitor. Hysteresis ...
0
votes
2answers
94 views

What is the need for a pull-down resistor in this schematic?

here at the second page: http://www.skyeinstruments.info/index_htm_files/W200P%20Windvane.pdf there is an external 470k resistor in parallel with the measuring device. it seems like the manufacturer ...
0
votes
1answer
68 views

Inductor held with hands

I have a fairly simple problem, but as I am a newbie in electrical circuits I was hoping someone might help me understand the principles of things. I have a circuit with an inductor of L = 0,102H a ...
0
votes
1answer
66 views

Why isn't this LM2917 circuit working to turn off a transistor?

It was suggested to me that I should post a new question (original question here: Minimal Hall effect sensor circuit to keep something off after certain RPM achieved). The below schematic is for ...
-6
votes
2answers
79 views

What should be the value for the resistor for this circuit?

Sorry for this silly question but I am not from an electronics background. I am trying to build a very basic circuit with npn transistor to detect a certain water level. I am assuming the resistance ...
0
votes
2answers
75 views

How to find the expression for Vout?

I have that circuit and I need the equation of Vo, I've been told that I can solve it by the Kirchhoff method but I'm not sure. Is there a way that the expression looks like Vo=K(V2-V1) ?
0
votes
3answers
104 views

Is there a non recursive formula for mixed resistors?

In equivalent resistors in multiple parallel resistors, like this simulate this circuit – Schematic created using CircuitLab I need a formula for the equivalent resistor for the whole ...
0
votes
2answers
93 views

Calculate mosfet gate resistor?

I got this schematic : In the image you see; I'm driving two infrared leds at 40 Ma each one with a FDN327N Mosfet. Attached at D8 there is one of Teensy 3.1 digital output that has HIGH voltage ...
8
votes
4answers
996 views

555 timer: how to set values to take an hour

I'm new (and novice) in electronics. I came to seek your knowledge to see if someone can help me with a very basic circuit. It is a 555 chip, which should light a LED (for about 1/2 second) every ...
0
votes
1answer
78 views

Calculation of base current resistor resistance for a transistor operating in switch mode? [duplicate]

I have a 9V DC motor and I want to control its speed with an Arduino board with help of a power transistor TIP120. In one of the web-tutorials the writer explains how to calculate the resistor ...
0
votes
1answer
95 views

9v battery to parallel 3v LEDs - burnout

I'm having an issue in a simple (n00b) LED circuite - ended up burning out a couple of LEDs due to some mistake I'm making, but can't figure out what the error is. I've got a 9v battery, trying to ...
0
votes
1answer
37 views

MAx peak to peak of ES without clipping?

This is an exam problem in which my instructor gave the answers but no work. Any one has an idea of how to solve it;FOM(figure of merit)= 25/125, RL=15 ohms, Rx=250 ohms, r1,r2,vee,vcc, are not given. ...
1
vote
4answers
467 views

Turn a transistor on when any one of nine LEDs is on using an LM3914

I'm wanting to turn a transistor on when any LED from LED2 through LED10 are on with an LM3914 in dot mode. Basically, I want the transistor to be normally off until at least LED2 begins to light ...
0
votes
1answer
73 views

Make three respective LEDs blink with an LM3914 in dot mode

I'm trying to figure out how to make in the below schematic, LEDs D2, D3, and D4 blink respectively while the LM3914 is in dot mode when their on state occurs. Basically this would act like a warning ...
0
votes
3answers
99 views

Resistors in series or one after?

I want to use a Voltage divider and i need to divide 5v to ~3.3 so I ordered 10K resistors on eBay, but the voltage divider needs a 20K and a 10K, can i use 2 10K's parralel as a 20K
1
vote
1answer
35 views

Power resistors equivalent thermal model: Interpretation of datasheet & 0°C terminal of power source

This is borderline electronics, but I think many more of us here have done this kind of studies. I'm heating an aluminium plate with an Aluminium clad power resistor by mounting it on it and applying ...
-1
votes
1answer
90 views

What are the failure modes of resistors, inductors, capacitors, diodes, transistors in conditions of overvoltage or overcurrent? [closed]

What are the failure modes of resistors, inductors, capacitors, diodes, transistors in conditions of overvoltage or overcurrent? Example: ...
0
votes
1answer
66 views

Resistance calculation for transistor base

I read this question's answer on calculating the base resistor value for a 2N3904 transistor. I'm in a similar situation however I'm using a TIP3055 to switch a \$V_{CE}\$ of 12V and a \$I_{CE}\$ of ...
0
votes
1answer
61 views

Multiple shunt resistor INA226

For a project I'm trying to build a measurement tool for USB where I can measure U, I and P using the INA226 from Texas Instruments. The shunt resistors all have a different value to measure a ...
1
vote
6answers
425 views

Need to build a circuit resembling fluid flow through porous media

I am trying to use electronics analogy to build a model that describes fluid flow in a porous media. For example I consider voltage, current and resistance to be equivalents of pressure, flow rate and ...
2
votes
2answers
67 views

A simple RL circuit, getting transfer function, matching with results

I'm doing little lab exercise with an RL circuit. I need to check if I did this analysis right, because the numbers I got and the numbers that should theoretically be there are so far off, I figured ...
1
vote
1answer
90 views

What happens when the voltage drop does not equal voltage rise in a closed series circuit?

New to electronics. Can't get my head around so many basic things but the application of KVL is bugging me the most. I want to know what happens when Kirchoff's voltage law is broken. If for example, ...
1
vote
2answers
62 views

Problem with a circuit of an controlled variable voltage source

I have this circuit, it should regulate the output voltage between 15V and 0V. But the output I get when I simulate it is between 2V and 3V, and when I implemented, I burned zener diode 1N4734A. ...
2
votes
1answer
72 views

Can I extrapolate the rated overload spec of a wirewound resistor to a joule rating?

I'm considering using a Vishay FVT series resistor for precharging some capacitors. Capacitance: 3300uF Voltage: 730V Resistance: 500 ohms Resistor continuous wattage: 25W This series, like many ...
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votes
2answers
138 views

Can I use DC resistor in 220 V AC circuit?

Can I use DC resistors as AC resistor? If yes, is there any problem interfacing with it? Please recommend AC resistors for working with 220 V AC 50 Hz.
1
vote
1answer
39 views

How to wire multiple 2 volt flickering LEDs to work on 12V auto system

I have tried to use the site to find an answer to this, but it seems everyone that has asked questions have different variables than I am dealing with, and I can't ever seem to grasp electrical ...
1
vote
2answers
270 views

How to measure current practically in a circuit

I have to measure this circuit, I have done the theoretical calculations using Kirchhoff's 2nd law, but I'm having troubles in measuring the current in each part of the circuit: I have to measure ...
0
votes
1answer
88 views

Toggle transistors with an shiftregister to light up an LED

First of all I'm quit new to electrical engineering. I had it 3 years in class but I didn't do well. So here is what I plan. I got some shift-registers (74HC595) Which I'll set with an arduino mega ...
2
votes
0answers
152 views

Integrated LED + Resistor + Transistor

Most designers when are controlling an LED have to make the same old circuit of Vcc -> Resistor -> LED -> Transistor (you need the transistor in case your ...
2
votes
3answers
177 views

Rule of thumb for LED Ballast Resistor

As well all know, using an LED without some sort of current control is a bad idea. One of the most basic types is a simple Ballast Resistor, paired with Ohm's Law. Based on Vin, Vf, and the desired ...
0
votes
1answer
51 views

Drain Li-Ion battery by connecting USB +5V and GND

I have a sportswatch which can be connected to a PC via USB for downloading the training information, upgrading the firmware, etc. I have used those features for a year on weekly basis, but since ...
0
votes
1answer
45 views

Why is voltage properly siphoned off in this circuit?

This comes from the Raspberry Pi "fart detector" project. It says to place a 47k Ohm resistor connected to ground in order to siphon off a certain amount of voltage so that the voltage read from the ...
0
votes
1answer
49 views

Heat dissipation

I have a computer power supply and I'm wanting to make it a variable voltage power supply but I have to have a load on it which requires some resistance. I have connected a 10 ohm 10 watt at 10% ...
1
vote
1answer
101 views

LED's too dim. Wrong resistor?

I'm a halloween tinkerer, and I have these UV/Blacklight flashlights that I use in my decor, but they eat batteries like crazy. They start going dim within an hour or so. So, since I already have ...
0
votes
0answers
138 views

Calculating the resistor's power consumption of 1 ohm in watts

I ran into a old-midterm exam question that calculate the one-ohm resistor's power consumption in the following diagram in watts? I need some solution or hints. I try to solve it but I think the ...
0
votes
1answer
98 views

What's the thermal time constant/capacitance of a 1/4W resistor?

I can't find it anywhere, what is the thermal time constant or thermal capacitance of a standard discrete 1/2W resistor? A table with other resistors of different power ratings would be nice, too.
0
votes
2answers
48 views

Why does a headphone attenuator need separate resistance for each side instead of a shared resistor for both?

I have a Shure headphone attenuator and opening it up it looks like there are separate pins on the pot for the left and right speakers (the pot has 5 pins, which I believe are left in/out, right ...
3
votes
4answers
635 views

DC Motor + 9 V battery + 270 ohm resistor = Nothing (Motor won't turn)

I'm trying to wire up a DC motor to a 9-volt battery with a resistor in between, and the motor just won't turn. It works if I connect the motor directly to the battery, but not with the resistor in ...
0
votes
1answer
73 views

Touch dimmer with low voltage transformers, needs incandescent to work? Updated!

I've looked extensively about this topic, and can't find any answers. Hopefully someone on here can help. I live in Texas and have 120V power in my house. I'm using a lamp touch dimmer to dim two ...
1
vote
1answer
102 views

What does lumped element mean?

Can anyone explain me the meaning of lumped element and lumped circuit abstraction in detail. What does lumping or discretizing matter mean?
0
votes
1answer
73 views

Calculating total resistance for this circuit?

I'm very lost in my ECE class right now and I was hoping someone could help me out and explain what they're doing. I was asked to calculate the total resistance. After getting that, I was asked to ...
-1
votes
1answer
64 views

AC source in parallel with resistor problem [closed]

For an AC source of for example +-12 V, can a connected resistor at any instant, have 24 V across it? Because my textbook has a problem in it involving such a source and says (hint: consider the ...