# Questions tagged [basic]

Fundamentals of electricity, electronics, components, or theory

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### Is there a need to ground an isolated electrical circuit? [duplicate]

It seems to me that every time there happens an electric shock through the contact with the ground, it happens because there is a difference of potentials between the contact point and the ground (for ...
725 views

### Problem with equivalent resistance

I have a problem determining equivalent resistance of this circuit. The previous assignment had the battery between C and 3R1 resistor, and i knew how to calculate the equivalent resistance. I ...
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2k views

### What is a multimeter at its core?

We know that, thanks to Ohm's Law: If you have an ammeter, you can put it in series with a resistor of known (usually large) value and now you have a voltmeter (after rescaling ofc). If you have a ...
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35 views

### Setting up equations for current, voltage and power analysis of linear electrical net

The directions of currents are throwing me off a bit. I think I should use mesh analysis here, but I'm not sure about the exact equation. For example, in the topmost mesh, should I write -120v + 20i1 =...
113 views

### Driving a LED with a potentiometer in parallel, electronic basics

Today, in class, we were to analyze this circuit: simulate this circuit – Schematic created using CircuitLab And calculate $\alpha \in [0, 1]$ associated with R2 a potentiometer. I'm confused ...
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1 vote
47 views

### Why there is a resistor connected between terminal and the ground? [duplicate]

Why a resistor is connected between non inverting terminal and ground?
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642 views

### Can an opamp have a negative gain?

I have a school excercise which I don't fully understand. The excercise is that you build an opamp circuit with a negative gain, -40 and a bandwidth of 100KHz. The gain-bandwidth product is 1000 000. ...
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48 views

### How to input range of current values in LT Spice

Firstly, I'm a beginner at LT Spice. I wanted to learn how could you input a range of values for current. For example, let's say, I want my waveform to oscillate from 10uA to 10mA in the circuit below ...
89 views

### Are Arduino inputs equivalent to voltage measurement?

I read somewhere that Arduino input pins basically (more or less) just measure the voltage at their pins with respect to ground (and then, based on that, create an analogue value or a digital HIGH or ...
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35 views

### What happens if we give a negative trigger pulse before a monostable multivibrator reaches it's stable state

Monostable Multivibrator using Op Amp, from this link, Obviously there is a certain amount of time that the capacitor takes to charge again from -Vcc*β to VD (0.7v) and therefore during this period a ...
604 views

### Voltage drop over open circuit

I am still learning the basics of electronics and this confused me: I have a simple LED circuit like this (5V voltage source): The LED has a specified voltage drop of 3V, and is rated for currents of ...
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31 views

### Newbie: A 4-wire stepper motor whose colors don't correspond to those from driver. How to wire?

I have a 4-wire stepper motor (https://www.researchgate.net/figure/NEMA17-Stepper-motor-data-sheet_fig9_313427253). I know by testing that the A,A' circuit is [green, red] and the B,B' circuit is [...
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99 views

### Simple e-stop circuit

I have a motor controller that has an electronic stop function where if I put 5v on a pin the motor runs. Once that 5v gets interrupted (goes to ground) the motor stops immediately. On my device I ...
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72 views

### How do electronics (like transformers) convert high voltage, low current to low voltage, high current, and vice versa?

I am fairly new to tinkering with electronics/electronic-adjacent ideas and I have been wondering: how do electronics get the desired voltage/current to operate properly? I understand in AC power, ...
215 views

### Measuring latency on photodiode

Attempting to measure latency on a photodiode. This is the circuit I've put together: Source TS7805 to give my 5V (from a 12V rail) 1.2kHz square wave into first T1 D1 is a BPW41 scope on source and ...
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545 views

### My textbook claims that base kW = base kVA, but doesn't this equality break down when power factor isn't zero?

I am new to per unit quantities, and have tried various combinations of search terms on Google over the span of a week and a half but I'm finding myself still stuck. In the SI edition of Power Systems ...
227 views

### Self inductance vs loop area of inductance. How to combine them/which to pick in which case?

When it comes to inductance in circuits, it is a rule of thumb to minimize the loop area. This implies a return path (i.e. two wires). There is also self inductance of a single wire. I am not sure how ...
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1 vote
107 views

### Why is there a voltage when following a larger resistor versus a smaller one?

I'm given two otherwise identical circuits with +3V input on the top and -3V input on the bottom. There are two resistors between these voltages and an ideal diode between those resistors alongside a ...
73 views

### simulation (in Falstad's app) of thyristor using transistors fails

I am trying to simulate thyristor behavior with transistors PNP and NPN but it fails (is it a bug of app?). When lower switch is open(and was never closed) and upper closed then current flows through &...
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1 vote
56 views

### How does the flux density act on the conductor in the slot of a rotor?

Following picture shows north pole, airgap, rotor. The conductors are placed in the slots. It seems almost all the flux density is passing through the low reluctance rotor metal part. Not much flux is ...
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41 views

### How does the speed stay fixed when the resistance of conductor is 0?

My textbook has the following example of hypothetical linear motor. A current carrying conductor is placed in a magnetic field. The conductor is attached to a variable load(pulley+weight). How it ...
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96 views

### Is my interpretation of voltage, amperes and ohms correct? [closed]

This is probably a very common question, but I feel most metaphors are somewhat simplified and therefore lack accuracy and I think that makes me unable to fully understand them, but I've looked at it ...
41 views

### Why is dynamic power in this simulation with rectangular input voltage wrong?

The following circuit models the output of an inverter (voltage magnitude is 1V). simulate this circuit – Schematic created using CircuitLab The dynamic power should be independent of R1 and ...
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105 views

### Physical circuit not drawing as much current as my calculations show

I've created the circuit below and have calculated the following values: R' (equivalent resistance of entire circuit) = 1 / ((1/470) + (1/470) + (1/470)) = 157 ohms I1 = VBattery / R1' = 6V / 157 ...
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1 vote
65 views

### What is the current induced in a wire connected to an ideal transformer using Faraday's law?

Imagine an ideal transformer interfacing an ideal current source with a ramp function $i_1(t)=a t$ connected to the primary winding and a resistor $R$ connected to the second winding. We want to ...
1 vote
181 views

### Controlling 0-5V from 0-3.3V PWM pin and 5V power

What I have is I think a standard problem in home electronics but I can't wrap my head around it. I'd like to control an IKEA light chain from an ESP32 board. The chain is basically a set of LED ...
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113 views

### Why does this circuit flash the two LEDs even without a 555 timer?

Can you please help understanding how this circuit is flashing the two LEDs? I know about transistors, capacitors, and resistors functionality, but can't get how this works without a 555 timer.
91 views

### Parallel resistors connected only on one side?

In this diagram, with four different resistors, in the lower circuit, we know that the voltage across all resistors is the same, and the currents are different. With the formula 1/Rn = 1/R1 + 1/R2 + ...
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89 views

### What difference does it make if we touch an electrical appliance with wet hands? [duplicate]

This perhaps looks like 8th grade question. I have two different scenarios: I am handling an electrical appliance with dry hands. I am handling an electrical appliance with wet hands. It is often ...
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66 views

### Coil generator in practice

I am trying to create something like gyroball. Which features LED lights, so the faster the spinning, the more light LEDs emit. This seems like a simple scenario of a coil generator. As an experiment, ...
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73 views

### Clarification: the role of resistance in producing heat / light (e.g. incandescent lightbulb)

I'm reading Code: The Hidden Language of Computer Software to get a better understanding of what makes a computer work. Early on there is some elementary explanation of what electricity is, and how we ...
46 views

### Calculating current -- Thevenin?

Can someone please remind me how to solve this very basic calculation? I've got a Wye configuration of resistors and am giving DC values 1V, 2V, and 4V to points A, B, and C respectively. I want to ...
1 vote
93 views

### PNP- NPN light flasher

I understand that R1 and R2 make a voltage divider. initially Q1 is not conductive, so is Q2? initially C1 acts as short circuit, so flashes the light L1 for a moment? Please correct me if wrong. ...
112 views

### Big confusion about the very fundamentals of circuit analysis

First, let's call IR3 the current flowing from A to B, IR4 the current flowing from B to C, IR5 the current flowing from C to (-V2). What's the proof that IR3>0, IR4>0 and IR5>0? I know this ...
1 vote
181 views

### Help understanding a simple amplifier circuit using a single transistor

I'm reading Electronics for Dummies. So far it's great for a complete beginner, however, I've come to a chapter about transistors and either I've missed something or there's a sudden jump in ...
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65 views

### Can I syphon power from a USB-C smartphone and still charge the phone?

I'm designing a device (simple 5V LED) that will be powered by a smartphone (via the USB C socket). I am struggling with allowing the phone to be charged at the same time via the same connection. Is ...
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50 views

### non-ideal op amp closed-loop gain derivation

How do I derive an expression for v_o / v_s? This answer fills some gaps but it doesn't tell me how they came up with the expression for V^- (corresponding to -v_d in my notation). ETA: here's what I'...
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409 views

### Output composite video (PAL) signal from FPGA DAC, totally lost in the analog domain

I'd like to start generating (and perhaps also capturing) composite video (PAL) signals from a digital source, eg. FPGA. However, while my digital logic/programming skills are covered, I'm lacking a ...
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259 views

### Simulation not working well in Proteus 8.12

I'm not understanding Proteus or something I'm doing wrong, and it's really basic, I put a 9v Battery, a Red Led, simple circuit and a 10k resistance, so the led shouldn't turn on right? Well, is ...
273 views

### Does a floating load on a transformer have no voltage difference with ground?

I think I know the answer, but I'm unsure. I'm studying for my FE, and in the practice exam is the following question: An ideal transformer connects a 120-V, 60-Hz voltage source to a load. One ...
60 views

### Basic RL curcuit problem

So I had an exam in basic electronics, which I passed but lost a lot of points on one seemingly easy task. "Through the coil is passing a current equal to $i_L=200\sin(10^5 t + 210°)$. If R=5 ...
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60 views

### Am I overthinking this simple power supply connection?

I want to connect a 12V fan and a motorcontroller to this generic ac to 12v dc power supply. The motorcontroller is pulling around 25 amps, and the fan about 1. I'm just wondering, should i add a ...
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245 views

### How to find current through inductor when connected in series with an ideal diode?

Please help me with this simple circuit, which is creating lots of confusion due to different results from theoretical calculation and SPICE simulation. Ques: In this circuit switch is closed for time ...
144 views

### Resistors in series to increase maximum Voltage

Do the values of resistors matter when I want to use them in series to increase the maximum voltage they can handle? So can I just use a 1 megohm resistor for example that's rated for 200 V and then ...
139 views

### Controlling a motorized ball valve and appliance with a float switch(es)

I am trying to create some redundancies for a small commercial ice maker to prevent there from ever being a flood in my garage. The ice melts from the ice bin (which holds around 80lbs of ice) ...
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358 views

### Undervoltage lockout

I would like to do a simple undervolatge lockout. I thought a BJT as a switch like this: In normal conditions I would have 30V (and -30 and the othre rail) and 25 mA to 50 mA. These power rails will ...
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83 views

### Power Supply stopped working after soldering

I am new to electronic circuits. I built a basic led circuit on a breadboard to test everything out.It worked as in pictures,but the connections were not stable because the holes were very large.I ...
1k views

### How to get negative voltage?

There's a bunch of posts about this, but they're all for very specific scenarios. I'm a newbit, and some components, like op amps, require both a positive, and negative voltage. But how do you get ...