It's a measure of how much an conductor opposes current flowing through it. It can also refer to a part of a circuit, which has a non-negligible resistance value.
1
vote
1answer
2k views
How to calculate current and voltage draw of a single resistor circuit?
If I have a single 270 ohm resistor connected in a circuit to a 3.3V 50mA power supply, how can I measure the voltage and current for the resistor? I'm familiar with Ohm's law V=IR, where V is the ...
1
vote
2answers
252 views
How does audio get transmitted from my iPod to speakers?
I need some help understanding a simple concept. I understand that my iPod/any other audio device sends electrical signals to my speakers/headphones.
From my research so far, an analog signal is ...
0
votes
1answer
118 views
what is the resistance of hydrogen?
If I were to connect a bettery to the two sides of a container that contain only hydrogen gas, and its not dense (it's pressure is one atmosphere), what would it's resistance over the length of the ...
6
votes
1answer
499 views
Requirement to display 3 mm LED by 220 V AC supply
I want to power a single 3 mm LED by a 220V AC source. For this I think I need one LED, one resistor and one capacitor. I don't know the needed resistor value and circuit diagram. The circuit also ...
5
votes
3answers
382 views
Calculating Rout of a bjt while using correct RL
I'm studying the notes of my professor of electronics, and I'm noticing an inconsistency of \$R_{L}\:\$ compared to what I've seen around in books and on the web. Here's what is considered ...
1
vote
1answer
74 views
How do different kinds of motors behave electrically under operation?
This is sort of a follow-up to this topic: Overclocking my toothbrush
I have since measured some numbers with my DMM. Remember this is a tiny brushed DC motor in a $5 toothbrush that I am driving ...
1
vote
3answers
313 views
Electronically switched decade resistance box design
I'd like to design a decade resistance box that uses a microcontroller to control the resistance.
Would it be possible to switch between different valued resistors using transistors? (or another ...
1
vote
1answer
181 views
Designing a water boiler?
I know this is very basic, sorry. But what material do I need to have enough resistance to boil water with the 120V household outlet?
Thank you
4
votes
2answers
225 views
Understanding electric power
While in a mood to purchase a Peltier strip, I visited the amazon page which stated the specs of a Peltier thermoelectric cooler, one stated 12 V and 92 W and other one stated 12 V and some 77 W.
As ...
0
votes
1answer
265 views
MOSFET sub-threshold operation
I have a question related to the sub-threshold operation of MOSFETS.
Let's say I have the following setup:
How can I calculate the sub-threshold current ( Id when Vgs < Vgs(th) ) at
Vgs = 0.5V ...
1
vote
3answers
677 views
How do electrical body fat detector work?
I would like to build me own electrical body fact calculator from a microcontroller (the Arduino), but I would like to know how does it work. I have a 5V analog reader, So I guess I sould calculate ...
0
votes
1answer
219 views
Strain gauges burned out in half bridge
I've been using a full wheatstone bridge (4 strain gauges) to read stress on a steel bar, through a circuit mounted on an arduino breadboard. This seemed alright. I later used two strain gauges of ...
2
votes
3answers
587 views
How usable can results of measuring MOSFET resistance with a multimeter be?
When the resistance of a MOSFET at a certain gate voltage and current is needed, the correct value is ordinarily obtained by reading the datasheet for specified values.
Since a MOSFET is supposed to ...
2
votes
3answers
496 views
Measure the resistance of some DC Motors
I did the following to measure the resistance of some DC motors I have and I'm wondering if I did it properly and if my conclusions are sound :
I had 4 motors (same model) already connected to a ...
5
votes
8answers
1k views
How does the electricity “know” the ratio of the resistance in a voltage divider?
I'm having a hard time conceptualizing what/how things are working in a voltage divider setup. I've read a couple other questions/explanations where the answerer has said to "not think about it in ...
1
vote
1answer
434 views
Wattage calculation for resistors in series
I need the formula for calculating resistor wattage when the resistors are in series. For example, say I have 3 1/4 watt 10 ohm resistors in series. What is the potential power dissipation for the ...
3
votes
1answer
448 views
Zero Cross Detection Circuit for line voltage [duplicate]
Possible Duplicate:
How can I detect a power outage with a microcontroller?
I'm doing some research with the goal of eventually creating a light dimmer controllable from a micro controller. ...
2
votes
2answers
217 views
In general, why do capacitors have a higher tolerance than resistors?
In general, why do capacitors have a higher tolerance than resistors? Capacitors have a tolerance of around 10%-40% while resistors have smaller tolerances generally. Why is that?
1
vote
2answers
2k views
Connecting LEDs to a 9V battery
1) I have 6 4.5V 20mA LEDs and have connected them to a common 9V battery. Doing this I made 3 parallel circuits with 2 LEDs in each.
Now, I see that most pages that describe LED circuitry say that ...
0
votes
2answers
253 views
Rotation sense of a potentiometer
I've been making an audio amplifier, it works well so far after getting the correct components. I'm using a 10K potentiometer with switch for the volume but I've got a problem. The potentiometer ...
3
votes
3answers
162 views
wirewound adjustable resistor. Something I missed?
I am by no means an expert on electronics, but I thought that I had a fairly good grasp of the basics. That is, until 10 minutes ago.
1 picture ~ 1000 words, so here is what I have:
The yellow wire ...
2
votes
1answer
237 views
Safe resistance for speaker jack
What would you consider to be a safe resistance for a speaker jack on a computer? I want to make a speaker unit for my laptop (which has awful built in speakers), but I'm afraid I'll end up drawing ...
4
votes
1answer
274 views
What is the physical meaning of resistance and power ratings of a loudspeaker?
What exactly does it mean when it is specified that internal impedance (or resistance?) of a loudspeaker is 16 \$\Omega\$? Is that ohmic resistance of the copper of its internal winding? Or is it ...
5
votes
2answers
236 views
What would the current be if I plug an LED into a perfect circuit
If I had an LED that had a forward voltage of 2.2 volts with a forward current of 20mA and I somehow created a battery that was exactly 2.2 volts and I put that LED, and only that LED, on that ...
1
vote
2answers
425 views
Way to discharge solenoid without (heated) resistors?
Here is a simple simulation of a schematic for my solenoid:
Once the switch is closed, the solenoid will be activated with ~80mA charge. When it is open (where the screenshot is at) it will ...
9
votes
2answers
1k views
Resistance Vs Impedance?
What is the difference between the Resistance and Impedance?
When we will say it is an Impedance and when we will say it as an
Resistance?
Can you explain it with diagram (If possible) and real time ...
1
vote
1answer
486 views
Shunt resistance VS Rogowski Coil in current measurement , which one is better?
Shunt resistance VS Rogowski Coil in current measurement , which one is better ?
Just for reference I want to create small circuit that measure the power , so which one I go for ?
UPDATE 1 :
I'm ...
1
vote
1answer
1k views
Operation of infinite switch
Many electric stovetops are operated by an infinite switch, which pulses the current on and off for intervals determined by the dial setting. The actual control is effected via a bi-metal switch that ...
0
votes
1answer
358 views
difference between output resistance, ro, and finite output resistance Ro?
What is the difference between the concept/meaning of output resistance, ro, and finite output resistance Ro in context of a circuit with MOSFETS (ie. a MOS current mirror)?
thanks
4
votes
1answer
106 views
Transistor terminal impedence?
Can some one explain the concept of transistor terminal impedance? What is it, and why is it important?
Any links to useful notes/resources will also be greatly appreciated.
3
votes
2answers
1k views
Do transformers use Aluminium windings?
Looking at wikipedia on resistivity I see that, other than gold, aluminium is a close second to Copper.
Do any transformers use aluminium windings ? I'm guessing they would be less expensive to come ...
7
votes
4answers
541 views
How to know that I am grounded with an anti-static wrist strap?
The resistance of my Belkin anti-static wrist strap shows 0.983, but how do I know that I am grounded by attaching it to computer power supply alone? See the picture below.
How do I know if that ...
4
votes
4answers
585 views
What should I expect the low end of my multimeters resistance measurement range to be?
I have an old Fluke 79-III and I'm trying to check the resistance of some resistors which should be 0.22 Ohms. Unfortunately, they are all reading 0.6 Ohms and so I'm wondering how accurate I should ...
3
votes
1answer
172 views
Can Z (impedance) have an φ of -105°?
Given a simple circuit with one voltage generator and one other circuit element, if these values are given:
U = 200 ∠ -45° V
I = 5 ∠ 60° A
(both values are phasors - I just don't know how to ...
10
votes
2answers
2k views
Correct formula for LED current-limiting resistor?
I'm trying to work out what value resistor to use in a LED circuit. The equation I'd use to do this is:
$$ R = \frac{V_{cc} - V_f}{I_f} $$
Seems logical, and makes complete sense. The answers to the ...
2
votes
1answer
267 views
Stripboard resistance
I am building an ozone measuring device and am getting inconsistent and sometimes non-existent results from the sensor. the sensor is mounted separately on a piece of stripboard on the lid of the box ...
1
vote
1answer
143 views
Mismatched Pull Up Resistors
Is it OK to have pull up or pull down resistors which aren't all the same value (if you're running low on components for example)? I can't think of a reason it should affect simple logic circuits.
...
1
vote
2answers
303 views
Hardware to Detect EMG or Skin Resistance
I have been given assignment to design a device that can detect emg signal of Skin Resistance change while moving
fingers.
actually i need to track finger movements using some hardware containing ...
4
votes
4answers
7k views
How do I calculate the resistor value for a simple LED circuit?
I have a simple circuit:
The max rating (current) of the LED is 30mA.
How can I work out what the resistance of the resistor needs to be? By using ohm's law I found it to be \$3V/0.03A = 100 ...
3
votes
3answers
563 views
What is the typical on-resistance of an MCU output?
In my case I am using PIC24F and dsPIC33F microcontrollers, but where is the on-state resistance of an IO port for a PIC stated in the datasheet? I cannot find it anywhere. And how does this apply for ...
2
votes
2answers
303 views
Potentiometer values don't add up
I'm working on a project that involves swapping out a couple of pots of a circuit board for a couple of digital potentiomters. I'm trying to make sure that I'm using the right resistance values, so ...
6
votes
3answers
249 views
Can I use an inductive load in an ATX-to-bench supply project?
I'm doing my second ATX-to-bench supply conversion, and this time, I've decided to follow the "book" and place the correct minimum loads on all the rails instead of merely the 5V rail. This involves ...
3
votes
2answers
223 views
Lengthen a AC to microUSB phone charger cord?
Can I effectively take a 3 ft standard cell phone charger (AC to microUSB, 750 mA at 5V) and lengthen the cord to 6 ft by splicing the cord or am I going to lose something in the mix? Do I need to ...
3
votes
2answers
4k views
5V to 3V, calculate resistor value (or use diode?)
I want to connect this dv motor to the 5V output of an Arduino board. Of course I need to get the 5V down to 3V in order for the motor to function correctly. I've read that I could use a diode with ...
4
votes
1answer
446 views
How to test internal resistance on small lithium polymer cell?
I'm coming from a computer science background, and will be writing some software to automate battery testing. I have background in math, but little to none in physics or electronics. Please consider ...
9
votes
7answers
2k views
How to measure gigaohm resistors?
I've got an issue that appears to be caused by damaged resistors that are either open circuited or of too low a value due to contamination. The problem is that they're gigaohm resistors, so to a ...
12
votes
4answers
537 views
Simple Circuit Question
I've been playing around with an Arduino for a while now, and while I know just enough about simple circuits to get little projects up and running, I still don't know enough to figure out what's going ...
3
votes
1answer
291 views
Can Resistance of wires be ignored?
I'm trying to calculate the internal resistance of my rechargeable batteries and haven't got a single battery holder so using I am having to using Banana plugs and Crocodile clips for holding my ...
5
votes
4answers
308 views
is the resistance in ten meters of copper wire too high to use in a circuit powered by AA batteries?
I have a wireless security system at home, and the wireless node is too far from the receiver. I was thinking that I could splice about 10 extra meters of wire into the existing line to move the node ...
4
votes
4answers
1k views
Precise Resistance Measurement Techniques
This question is inspired by some basic questions on resistors I've read here lately.
What's the most accurate/precise technique for measuring the value of a resistor you can think of? What level of ...
