Tagged Questions

Fundamentals of electricity, electronics, components, or theory

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0
votes
1answer
72 views

Arduino + transistor to switch PC fan on/off

I have: an Arduino UNO a 12V PC fan with 1.68W rating (140ma). 2n3904 transistor 12V 500ma power supply to connect to Vin. What I would like to do is to simply use a digital output pin on the ...
0
votes
2answers
99 views

LEDs, Voltage and Resistors

I noticed that a Christmas Light uses 20 LEDs in series parallel, operated by 2 AA batteries (3V) without a resistor. I thought you always need a resistor? Would it be possible to run them on 5V ...
0
votes
1answer
61 views

Photo transistor in parallel

I'm a beginner and trying to figure out how this circuit works (its a simple circuit that glows an LED when dark) : https://www.youtube.com/watch?v=eIGWWKThprI&list=UUhtY6O8Ahw2cz05PS2GhUbg#t=65 ...
0
votes
1answer
39 views

Electronics by Example [closed]

I am interested in learning more about electronics. I know some basics about resistors, capacitors, transistors, and diodes. I would like to learn more about things such as operational amplifiers, ...
-1
votes
2answers
103 views

How do I solder to these pads?

Quick question. I'm trying solder some wires onto the 5 pads (top right of board) in the image. What's the best way to achieve this? I cant get the solder to stick to the board and I have no flux. I ...
8
votes
4answers
1k 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 ...
1
vote
3answers
86 views

How and why is a magnetic field transmitted with alternating current?

I apologize for the basic question (or if it is incorrect in its assumptions,) but how does one account for magnetism in alternating current? If I generate alternating current to a motor, why do my ...
2
votes
1answer
117 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?
5
votes
1answer
265 views

Mounting AC-DC converter on PCB

I need to figure out how to physically mount the following AC-DC converter to a PCB to be used as part of a regulated power supply. The pin height is min 3.0 mm. Should I mount it as a through-hole ...
0
votes
1answer
48 views

Should I assign currents to voltage sources in my circuit analysis

Mortals! I apologize if my question may seem, foolish, but I have a need of understanding a process in analyzing circuits. You see, when we are looking at resistors (non-sense, my lightning never ...
17
votes
9answers
3k views

Why are electrons not pushed out from the conductor at an open circuit under the influence of a power source?

Frequently, electric current is compared with water flow. For example, if I make a hole in a water tank, water will flow till the tank pressure and the atmospheric not become equal or the tank becomes ...
0
votes
6answers
116 views

Closing two circuits from one button press, with a delay?

From one button press, I want to momentarily close two circuits with a small (< 1s) tuneable delay in between. What term should I google for to find a schematic? (For clarity, I want to press the ...
0
votes
3answers
62 views

Working of RC Phase shift Oscillator?

Figure show a RC phase shift oscillator using Op-Amp with gain 5(Vo/Vi). My assumption : Circuit is generating a sine wave with a peak to peak voltage of 10v. Consider positive maximum point (+5V) ...
-1
votes
1answer
76 views

Components Purposes. Just need a verification

I just need to know if there is anything I need to add or remove. And also What is the purpose of a switch transistor(Q1)? I need a simplified explanation. Thanks in advance
-3
votes
2answers
125 views

Why does AC Current exists? [closed]

I need to know why does AC Current exists? And why not only DC current exists? Most devices needs DC current. I know that DC current is much dangerous then AC current. because of it is alternating ...
16
votes
3answers
2k views

What operation could cause the inductor or the capacitor to explode?

In really early days of electronic school, the teacher used to say something about not unplug power too quickly at an inductor or capacitor and we were used to slowly turn the voltage generator from a ...
1
vote
2answers
107 views

What are quartz crystal oscillators?

I'm a beginner in electronics and I found two quartz crystal oscillators, each one has two pins. Their numbers are: sjc4.000a ee4.000 Is it possible to know the ...
0
votes
2answers
149 views

How can two steel balls with same amount of charge be at different voltages?

Maybe this is the most fundamental question, but still it eludes me. Is it possible for two balls each containing 1 Coulomb of charge be at different voltage levels, say 1V and 2V relative to a ...
1
vote
1answer
72 views

Electrical Engineering Math, showing time independence? how?

I have a cheat sheet provided by the teacher about the calculation of the Coherence Time, however I get lost along the way. There are 2 paths of a signal at: Path 1: \$\phi_1(t) = ...
2
votes
3answers
201 views

What is Doppler Spread

What is the plain English explanation of the Doppler Spread? Looking at different sources I come across complicated definitions which I struggle to understand. Example for such one: Doppler ...
2
votes
2answers
72 views

What makes DSSS a more robust transmission technique compared to FHSS?

In many textbooks it is stated that DSSS is more robust than FHSS. Especially in terms of interference and delay spread? What is the exact reason. Lets say we multiply a given bit 1 with a larger bit ...
0
votes
1answer
66 views

Plain English explanation of the Space-time Code Block by Alamouti

I checked about the Space-time code block online, but all of the explanations are either short or too simple, or too mathematical and complex Could anyone here provide an explanation of what ...
0
votes
2answers
45 views

How are the Intersymbol Interference and Symbol Time (duration) related to each other?

In a lecture slide I noticed that OFDM(Orthogonal frequency-division multiplexing) mitigates the problem of Intersymbol Intereference over wireless systems because the symbol time is increased, in ...
0
votes
1answer
42 views

Generating a desired pulse train in Xilinx ISE software

Need some help with VHDL and FPGA since I am new to it. I have a Virtex-4 FPGA and I wish to generate a binary pulse train of 16 pulses from FPGA using VHDL programming. My desired pulse train will ...
2
votes
2answers
84 views

What phenomena does “Coherence Bandwidth”?

Could anyone please provide a simple explanation of what Coherence Bandwidth means, and how is that related to Delay Spread. I read some articles but they don't help me to form the relation between ...
1
vote
2answers
96 views

Explain Rayleigh Fading in plain English

For a couple of days I am trying to understand the Rayleigh Fading model, but I am failing to. I look at various articles and tutorials online, everything goes fine up to a points, but then a lot of ...
1
vote
2answers
423 views

Connecting a potentiometer

I know how to connect potentiometer, but to be honest I don't know why. I would really like to understand what I'm doing. From what I have read the input voltage and the ground should be connected ...
0
votes
0answers
60 views

Inducing Eddy current in wet clothes

Is it possible to induce eddy current in wet clothes and dry them using the resistance heat generated? I don't want to connect any wires to the clothes.
-2
votes
3answers
283 views

When should you use a transformer instead of a resistor? [closed]

I feel like this was something that was never taught by my instructor in physics. Is there a certain rule determine when a resistor should be used over a transformer, when stepping down voltage?
1
vote
1answer
135 views

Why would we need to ground an AC source?

I'm new to this field hence this weird question. Why would we need to ground an AC source? Why wouldn't it be enough to have just one pole to get an AC current going? I understand why it wouldn't work ...
0
votes
2answers
136 views

How to understand the “basics” of electricity? [closed]

I want to be a self-taught computer engineer ... massive goal, but it's what I want eventually. I check out textbooks and online resources, but I feel like I need a prerequisite somewhat -- I still ...
1
vote
3answers
147 views

Powering multiple relays

I'm trying to control five * 5v relays from a micro-controller. However I'm having issues powering more than two at a time Some notes The power source is a 800ma 10V ac adapter. 7805cv voltage ...
3
votes
1answer
56 views

Capacitor charging: do electrons migrate from the source to the dielectric?

Encyclopedia of Electronic Components - Vol1, pg:98 by Charles Platt Electrons from the power source will migrate on­ to the plate attached to the negative side of the source, and will tend to ...
2
votes
2answers
262 views

Why there isn't current in R3?

simulate this circuit – Schematic created using CircuitLab Why there isn't current in R3? Does it depends on the resistance of R3?
1
vote
1answer
107 views

How R equivalent can be found?

simulate this circuit – Schematic created using CircuitLab How R equivalent can be found (without using star delta connection)? the answer said 3/5R
2
votes
3answers
434 views

How can the SI unit of resistivity [Ωm] be interpreted?

The way I interpret the resistance \$R\$ of a resistor, which has dimensions \$ [\frac{\mathrm{V}}{\mathrm{A}}] \$ is: how many volts must be applied across the resistor to achieve 1 ampere of ...
1
vote
1answer
116 views

Do I need trivial resistor or not if V/I = zero or almost zero

As the title says, do I need trivial resistor or not if V/I = zero or almost zero? For instance: Assume I'm using 3V buzzer and 2V LED in series with an Arduino 5V pin. $$R = \frac{(3 + 2 - ...
0
votes
1answer
127 views

Replacing BJTs with power MOSFET

I have 2 x 2N2222 BJTs powering 2 relays of 200mA each. I am using 2 output pins with 500ohm resistors to power the transistors. After powering it the circuit not working well, while replacing the ...
2
votes
1answer
265 views

BJT base resistor

I read this post: Which resistor for NPN transistor base? But I still cannot understand the base resistor calculation. I need the transistor to be a switch to 5V 200mA relay. The base will get its ...
-2
votes
2answers
155 views

Learning electronic circuit design [closed]

Is there a good website or book to learn electronic circuit design from the beginning. I would like to learn more about basic electronic elements and how to use transistors appropriately in my circuit ...
31
votes
10answers
3k views

What is a Charge?

I'm a high school student. I love computers and electronics. Few weeks ago, I thought to build my own electronic gadget but, unfortunately I had not much knowledge in electronics. So, I decided to ...
0
votes
1answer
71 views

How do I wire up this relay?

I'm making this circuit: I've bought an Omron G5LA-1 non-latching SPDT relay. It looks like this (from the datasheet): I'm struggling to figure out how I wire this up though. I believe I need to ...
9
votes
3answers
2k views

Basic operation of a bipolar junction transistor

I've tried really hard to understand the basic operational principle of a transistor. I've referred to many books and been to forums but have never got a convincing answer. Here are the things I want ...
3
votes
4answers
431 views

Does free electrons from the conductor itself flow or electrons inside the battery flow?

Hello I am new to electronics. I read electricity works this way - some atoms have more electrons than protons. These free electrons flow through a conductor such as a copper wire. However, to induce ...
0
votes
3answers
116 views

Basic question about voltage

The voltage on capacitor is given by $$V_c=\dfrac{1}{C} \int i(t)dt$$ and the current is $$i(t)=0.4 \sin(2t-\frac{\pi}{4})u(t)$$ when u(t) is unit step function. May you show how to integrate the ...
0
votes
1answer
78 views

SSR function con control panel

I'm new in electronics and would like to build an electric brewery with an electronic control panel. I found on www.instructables.com one control panel and is described as in following image. Could ...
2
votes
1answer
199 views

How does a first-timer set up a correctly-grounded workbench / work-station?

I'm new here, and new to electronics in general. (for the most part … my [awesome] father had me building some simple robot-kits with him when I was a kiddo, but I'm getting into it “4srs” for the ...
2
votes
2answers
165 views

How does a NOT gate bypass the output?

I have found the basic tutorials on gates and the way they work. However, I'm not understanding conceptually how a NOT gate, when activated, bypasses the output. Circuit as follows: simulate ...
0
votes
2answers
75 views

Simple Capacitor Wattage Ratings

I am constructing a simple circuit to convert AC power from the wall to a 10V DC power across a load. I am fairly new at this though, so I have a question about how much power a capacitor can handle. ...
0
votes
1answer
162 views

How to connect 3-digit display and suppress leading zeroes?

I searched a little and it told me to use with more than one display, connect (Ripple Blanking Output) from most significant 7447 to the of the next 7447. Which number would be most significant? ...