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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Voltage measurement

With the 100ohm resistor sitting between my 12V power supply and my device it doesn't spin (it's a hard disk). I also tried to measure the voltage drop with a multimeter to no avail. It always shows ...
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1answer
62 views

Does the Y-Δ transform suffice for every resistor network?

Suppose I have a (finite of course!) network of resistors only. Is it always possible to calculate the equivalent resistance between any two points using only parallel, series, Y-Δ and Δ-Y (wye-delta ...
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4answers
73 views

Moving two elements from series to parallel

I got a small pizza oven with two elements (top and bottom), they are rated 115V 600W and they are connected in series, as we have 230V in Europe. Everything works fine, but I would like to control ...
3
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1answer
170 views

Achieving (near) exact voltage divider ratio

Often, I'll have a need to create a voltage divider that has a specific resistance ratio, to obtain whatever voltage I need on the output. For example, for a specific project I'm working on (creating ...
0
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3answers
76 views

Will connecting two batteries in parallel increase current drawn in simple led circuit?

I have a resistor diode circuit that I'm powering with a 9V battery. The circuit diagram below is a simplified version of it. The real one has 4 LEDs, 8 resistors. I want to deliver 30mA to the ...
2
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2answers
119 views

How to adjust linear voltage regulator equivalent?

I'm attempting to build a linear voltage supply. (I'm not touching the mains yet.) My first thought was to use an adjustable linear voltage regulator. Unfortunately, I found that linear voltage ...
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1answer
75 views

Led driver circuit 3.3v & 5v

Not long time ago, as i couldn't find a proper Mosfet to drive a high wattage led strip ( 5050,5630), i asked how to create a circuit that allows me to turn on properly the mosfets i already own. ...
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2answers
31 views

Circuit with switch - express the current for different times

Consider the circuit below consisting out of a capacitor C and two identical resistors R. For \$t<0\$ the switch is open and the capacitor is uncharged. At \$t=0\$ switch is shut and the circuit ...
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1answer
31 views

capacitor and resistor combination

I'm currently working on some simple circuits to learn about circuitry, and being a Physics major I have a pretty good grasp of the mathematics and concepts, but I'm a little confused about ...
2
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2answers
75 views

Using multiple current sense resistors in parallel to handle a high current measurement with cheaper resistors

I am measuring the current going to a motor using current sense resistors; however, in order to get a resistor that can handle the proper power, the price goes up way too much. My question is, can I ...
2
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3answers
390 views

Current flow through resistor and insufficient source

In a simple circuit consists of a source and resistor, according to Ohm's law, if 10V is applied to a 10 ohm resistor, the current flow through the circuit will be 1A. But what if the source in this ...
1
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1answer
53 views

What should be the size/package of Bob Smith Termination resistor?

We have run into a layout issue where the size/package of the 75R resistor used for Bob Smith termination on unused Ethernet pins is in question. The current package of this resistor is 1206 and we ...
1
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2answers
105 views

Resistor network explanation and calculations

First question - What is this resistor network doing? Answered that it's linearizing the thermistor but this isn't what I was looking for. I'm looking for an explanation that describes the ...
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1answer
34 views

Determine supply voltage for led from current limiting resistor

Everyone knows how to calculate the resistance of a current limiting resistor for a LED but is it possible to go the other way? (aka determine the supply voltage from the resistor's value) I ask ...
1
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2answers
56 views

Load Resistor for high amp low voltage testing

I want to simulate a signal of 15V / 30A through a device. I will use it to ensure that a series of prototypes are capable of switching at this current. $$ P = 15 \times 30 = 450W $$ $$ R = ...
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2answers
45 views

Resistor values for a passive audio mixer?

I'm trying to come up with a schematic for building a passive audio mixer for an aviation headset, but I'm having some questions about resistor values. Figuring out the general circuit is easy ...
0
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2answers
109 views

Is resistor on LED's necessary after voltage drop?

Let's say we have perfect 5V DC 0.1A power supply. Obviously for one LED we would need a resistor (I'm well aware of Ohm's law), BUT what if we connect bunch of LED's in series. And the current drain ...
0
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1answer
49 views

Driving MOSFET with 555 timer [duplicate]

I am building a plasma speaker using a 555 timer to generate the audio tone. I am driving a mosfet with the output of the 555 timer, which in turn powers a flyback transformer to generate a plasma ...
1
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4answers
165 views

How to test analog component before mounting?

I have been in a small factory today, they produced 4 kind of PCBs that all are simple analog boards, each month they produce 1000 of them. The problem is that till now, after mounting them almost 10% ...
0
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1answer
83 views

How do I amplify an input signal to match the peak of another signal

I would like to build building a Voltage Controlled Oscillator (VCO) for audio applications beginning with a relaxation oscillator build from op amps. Adding a potentiometer to the feedback loop ...
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0answers
25 views

Limit large currents in a small space?

I've built a variable voltage bench-top power supply from an old printer adapter. I cut off the output wires, and soldered in connections to a buck converter module and a potentiometer. The limit of ...
2
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1answer
35 views

Metal Film Resistor: Coating Reliability

I am using this Power Metal Film Resistor - which as per the datasheet, is coated with a "red, non-flammable lacquer which provides electrical, mechanical and climatic protection". Now, on my PCB, I ...
4
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3answers
445 views

What happens when a power metal film resistor is exposed to higher power?

What is the worst thing that could happen if a power metal film resistor rated for 2W is exposed to 15W due to a short in the circuit? I have seen smoke being emitted but switched off the power supply ...
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1answer
16 views

Avalanche diode circuit analysis of the current load

I have no idea how to work out this past exam question. I'm kinda sure is that the diode is an Avalanche diode, but I'm not even sure how Zener diodes or this work. All I think I know is that with a ...
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1answer
45 views

Maximum Power Transfer with complex source impedance

I have a question about maximum power transfer involving an AC circuit, where there is a Thevenin circuit with a complex impedance. If it's asking for the load to be purely resistive, how can I know ...
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25 views

Why cant I find a Force Sensing Resistor part definition in Eagle?

Below I have a schematic that I have used a generic resistor symbol with a label of "'FSR" to identify Force Sensing Resistors. I am used to using a different symbol. Is there a better symbol in ...
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1answer
60 views

How do I work out the time when given current in a RC circuit?

So this exam question looked straight forward, but I can't get the right answer. I'm trying to find the time, from when the switch is close,that the current will equal 2mA. I've used a few formulas ...
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67 views

Calculating resistance for driving motors off Arduino

I'm planning on driving two motors off an Arduino. Here are the two motors I'm using, requiring 3VDC and 350mA. It was recommended I use this H-Bridge to control the two of them, capable of driving ...
0
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1answer
61 views

How to use series resistors when connecting sensors to microcontrollers via SPI

N00b here; I have a sensor that I intend to connect to an Atmega 328P (AKA Arduino) running at 5V. I already understand why I need to use a pullup resistor on the active low chip select pin, but the ...
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2k views

Where did these Ohms come from?

I am new to electronics and am tyring to figure out something that is a bit disturbing to me. I am trying to figure out the amount of resistance I need to put in series before an LED, and the equation ...
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2answers
99 views

Help with an OpAmp

I need to show that V= 5*V1 - V2 Can anyone give me a hint so that i can proceed with the resolution? Thanks!
0
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1answer
71 views

Why isn't there a voltage drop across the Main Wires?

As far as I know the power to my home is directly coming through a Step-Down transformer, so why isn't there a voltage drop and how are all the houses hooked up to the same transformer getting the ...
8
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3answers
595 views

Choose the better values (in terms of range) for resistors in this non-inverting op-amp circuit

These days I'm looking at operational amplifiers; from what I've seen, implementing them in a circuit is quite simple, at least when they are connected as "non-inverting". Determining the ...
0
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0answers
51 views

Interfacing Constant Current to a Microcontroller

With reference to the circuit below, How can I control the SET from a Microcontroller? It really needs a variable resistor attached. I've looked at digital POT's although it would need to be ...
0
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1answer
51 views

Rechargeable Gameboy Color modification

I've been doing a little research online on how to make my Gameboy Color rechargeable, and I came across an instructable this guy made on how to make your GBC rechargeable using standard rechargeable ...
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6answers
801 views

Easy way to figure out a LED's Vf in order to pick an appropriate resistor

I was wondering what the easiest way to figure out a LED's forward voltage is, using measurement tools. I know we can assume red LEDs to be around 1.8V - 2.2V, and that we have similar information ...
0
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2answers
85 views

calculate resistor value for transistor base

Below is a circuit where S1 is the output of a 555 IC timer (S1 switch for simplicity). I need to invert the output which I have done so in another project using the circuit below. Starting with ...
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2answers
65 views

How can I lower voltage coming in to a kiln?

I have a small firing kiln. It heats up to quickly for my ceramic pieces. I was wondering if I could reduce the voltage coming into it so it could heat up slower ? And if I could how could I go about ...
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2answers
88 views

How do you arrange four 4-ohm resistors to have a total resistance of 4-ohm?

I have some understanding of circuits and I have solved most of the problems in my homework, but I've come across then one seen in the title and can't solve it for some reason. If someone could please ...
0
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1answer
63 views

Voltage help with resistor

Im using a 3.7V 18650 Li-ion battery (Ultrafire) and the circuit calls for a 27 ohm resistor. But one battery tested at 4V and the other 3.7V. Is the resistor too low now? Which rating should my ...
2
votes
3answers
109 views

Power dissipated in 0 Ohm resistor [duplicate]

I have seen many zero ohm resistors which says that maximum resistance is say 50 mOhm. But, the maximum current rating will be only 1 amps. 0603 package. Power rating they mention as 1/8 watt. Can ...
2
votes
4answers
308 views

Measuring a huge resistance on low voltage

I was thinking on this theoretical experiment for a while, but nothing useful came into my mind. We have a "resistor" (rather a material like plastic) with a resistance expected to be very high, say ...
12
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2answers
940 views

Unusual old resistor symbols identification

Image from: here. This image is the schematic of an old Tesla 521A valve amplifier radio. On the following resistors in the schematic there are weird markings: R4, R5, R6, R24, R25, R26 I am ...
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2answers
120 views

When to use a 1/4 Watt resistor vs 1/2 Watt resistor

I have never understood the difference between 1/4 & 1/2 watt resistors, and in all of my EE lab courses I have always just used 1/4 Watt resistors. When does one use 1/2 Watt resistors and what ...
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1answer
22 views

Power Metal Oxide Resistor - Maximum pulse voltage

I am looking for a suitable series resistor (220k) for a 230VAC optocoupler input. The device must meet requirements from EN60664-1. I am still trying to understand the final requirements, but from ...
0
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1answer
40 views

Proteus VSM: digital vs analog resistor and LED

I'm a newbie to electricity and electronics in general. I've been reading about the principles and have a basic understanding of them. I'm also diving into creating my first basic circuits with ...
0
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2answers
100 views

smd resistor and regular through hole resistor

My question is fairly simple. I am building an SMD LED board and i am limited in space. So originally i was planning on going with through hole resistors, but have it being i'm very limited on space ...
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3answers
81 views

pull down resistor in PIR circuit

I have an motion sensor circuit. The circuit calls for a voltage of 2-15 dc volts. On the PIR data sheet the source pins calls for a pull down resistor of 47K at 5 volts. My question is if I use 8 ...
0
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1answer
55 views

SPI Communication during Programming

I am using the ATtiny861a and have made it so that the SPI connects to a Radio and an external memory source VIA two different chip select pins but sharing the same MISO/MOSI/CLK line. Correct me if ...
2
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2answers
63 views

How to find the power delivered to the load?

I'm trying to solve a homework problem to find the power delivered to the 10Ω load. So far I found the total resistance, which is 12Ω. And I think I have the right formula to work out the power, ...