regarding circuits

[joe0311]

I'm just trying to learn about electricity/inventions for fun. Are circuits necessary for all machines to run? If not, what are other ways to deliver electricity to machines, and why do certain ones require circuits? What are some examples of ones that require them and ones that don't?

[Strange]

A circuit is just the connection between the components (which includes the power supply).

 

So all (electrical) machines require a circuit. For example, the connection from the battery to a motor is a circuit.

 

But perhaps you mean something more specific by "circuit"?

[joe0311]

Oh ok I see. I don't know hardly any terminology, but I've heard of capacitors and resistors, what makes something require those? I also asked a similar question on reddit and someone mentioned circuits are mandatory to do any sort of sequencing and I asked him what would make something require sequencing and he hasn't gotten back to me.

[Strange]

OK, so there are more complex circuits that may have capacitors, resistors, transistors or even microprocessors.

 

There are many reasons why these might be required from reducing noise (e.g. reducing unwanted radio interference) to controlling the light or the motor or making it more efficient or ...

Edited August 28, 2016 by Strange

[joe0311]

interesting, could anyone tell me some other examples of what these more complex components of circuits make possible?

[Strange]

Well, you compare a simple light switch with the more complex circuit of a dimmer that allows the brightness to be controlled.

 

Similarly, for some purposes it might be enough just to have a switch to turn a motor on or off. But the motor that drives an electric car has very complicated control circuitry with a microprocessor that runs very complex software to control the current through each phase of the motor. This is necessary to provide very precise control over the speed of the motor. (And also for efficiency and safety).

[Janus]

interesting, could anyone tell me some other examples of what these more complex components of circuits make possible?

Okay, here is a common emitter amplifier.

 

 

It contains resistors, capacitors and a transistor.

 

First I'll explain a bit about what the transistor does. It has three leads, a base, emitter and a collector. The basic operation is thus: if you connect a voltage across the emitter and collector, you can use current flowing between emitter and base to control the current between emitter and collector. A small emitter-base current can cause a much larger emitter-collector current. However, in order for this to work, there must be at least 0.7 "bias" voltage difference between emitter and base.

 

That's what resisters R1 and R2 are for. This is a "voltage divider", it divides the 30 volts so that there is ~2.2 volts at the base. C1 is the input filter. Capacitors have the ability to block DC current while letting AC( like the signal you would like to amplify)pass. Since any DC component coming in with the signal would throw the bias voltage off, we want to block it.

 

Re and RL perform two functions. One is to determine the amplification factor for the signal, and the other to to set the collector voltage. This needs to be chosen so that the amplified output signal won't drive this voltage too high or too low. If it gets too close to 30 volts or 0 volts, you get "clipping" or a distortion of the signal. C2 is the output filter, which prevents the DC component of the collector voltage from being passed on to the next stage (another amplifier, speaker etc.)

Sometimes a third capacitor will be included which is wired in parallel to Re, its job is to prevent the emitter voltage from varying with the input signal, by shorting the signal component of the emitter-base current to ground.

 

Capacitors also can be used in tuning circuits. Their ability to carry current is frequency dependent. If you've ever taken an old radio apart, you might have found something like this:

 

 

This is a variable capacitor and was part of the circuit that determined the frequency that you were tuned to.

[Sensei]

Oh ok I see. I don't know hardly any terminology, but I've heard of capacitors and resistors, what makes something require those?

Resistor is limiting current I.

I=U/R

Say we have voltage U=5 V, and resistor has R=100 ohm,

current I will be 5/100=0.05 Amperes. 50 mA (miliamps).

https://en.wikipedia.org/wiki/Ampere

Current multiplied by time, is Charge Q (unit Coulombs).

Q=I*t

https://en.wikipedia.org/wiki/Coulomb

 

Q divided by elementary charge e=1.602*10^-19 C, is quantity of electrons.

Q/e

https://en.wikipedia.org/wiki/Elementary_charge

If through circuit there is flowing 1 Ampere current, during 1 second period of time, it means there is 6.24*10^18 electrons flowing through it.

 

Electron flowing through some element, especially resistor, is losing part of its energy, and it's dissipated, and usually observed as heat.

Therefor large power resistors have heat sink or even fan.

Sometimes it's useful, when we need to heat liquid, like it's in heating element, in coffee/tea making devices.

https://en.wikipedia.org/wiki/Heating_element

Which is basically resistor with very large resistance.

1000 Watts power heating element with voltage U=230 V in the mains, has to have resistance around 53 Ohm.

I=4.35 A

U=230 V

P=4.35 A * 230 V = ~ 1000 W

R=230 V/4.35 A = ~53 Ohm.

Edited August 30, 2016 by Sensei

[joe0311]

Strange, Janus, and Sensei, thank you for your replies.

 

What is it about having a small current at the base of a transistor that can create a larger current at the collector?

 

Why is alternating current the signal you want to pass and direct current the signal you want to block?

 

What is the mechanism of capacitors that allow them to block DC current, or only allow current of a specific frequency to pass?

 

Is a variable capacitor what would be used to get a radio wave to go to the correct channel? And is this the component of the circuit that would allow you to change entities such as brightness, speed of motor, etc?

 

I really want to understand technology (various inventions) better, and I figure this type of stuff is a good place to start, so thanks for your help!

Edited August 31, 2016 by joe0311

[Sensei]

Capacitor in reality is gap in circuit,

gap made of air, gas, vacuum, insulator.

On the first electrode, electrons gather,

and can't travel anymore, as there is gap,

on the second electrode, electrons escape (electronical engineer would say "hole").

If too many electrons will gather and/or gap is small, electrons will fly through gap, and if it's made of insulator the most likely damage it, and capacitor won't work anymore correctly.

 

You should read about breakdown voltage of insulators

https://en.wikipedia.org/wiki/Breakdown_voltage

 

And is this the component of the circuit that would allow you to change the brightness?

 

For controlling brightness usually there is used variable resistor.

https://en.wikipedia.org/wiki/Potentiometer

 

Interesting element is also Varistor

https://en.wikipedia.org/wiki/Varistor

Edited August 31, 2016 by Sensei

[Strange]

What is it about having a small current at the base of a transistor that can create a larger current at the collector?

 

This is quite complicated. It is because the transistor consists of several layers of semiconductor material with different properties. Applying a voltage to the base effectively changes the resistance between the collector and emitter.

 

 

Why is alternating current the signal you want to pass and direct current the signal you want to block?

 

It depends on what you want to achieve. In this case, it may be because you are interesting in the alternating voltage because it represents the music you want to hear.

 

In some circuits you want the DC voltage but not the alternating voltage. For example to generate a voltage to charge a battery from the AC power.

[Janus]

Strange, Janus, and Sensei, thank you for your replies.

 

What is it about having a small current at the base of a transistor that can create a larger current at the collector?

 

A transistor consist of three layers of semiconductor material. Each layer has had a small impurity added in a process known as "doping".

Doping alters the electrical characteristics of the materials and produces two types, N and P. A NPN transistor consists of a as two N layers separated by a thin P layer. Because of the different properties of these materials, electrical current tends to flow more easily across the junction of two types (N and P) in one direction than it does in the other.

Applying a small voltage to the base (which is connected to the middle P layer) overcomes this barrier between emitter and base, But once this happens, because of the thinness of the P material, the current "sees" the junction between the base material and collector material, which attracts the majority of the current flow. ( think of it as the voltage between base opening a gate between emmiter and base materials. But once the gate is open, most of the current finds it easier to travel to the collector than out the base.)

 

 

 

 

Why is alternating current the signal you want to pass and direct current the signal you want to block?

 

 

In general, it is the variations in current that carry the information(like music) you want to pass on from stage to stage. to give you an example, let's consider a speaker. It produces sound by vibrations of the cone, the cone is vibrated by an electromagnet. variations in current to the electromagnet allows it to do this. Now let's say those variations were "riding" on a DC voltage (instead of varying around 0v they varied around some non-zero value.

There is a limit of how much the electromagnet can pull on the cone of the speaker before it has reached its maximum. If that non-zero value around which the signal varied is close to this, then the speaker will hit this limit and the sound it produces will be distorted. It is best if the signal varies around zero, so you can get maximum range from the speaker.

 

 

 

 

What is the mechanism of capacitors that allow them to block DC current, or only allow current of a specific frequency to pass?

 

 

 

As explained earlier, a capacitor consists of plates separated by a insulating material (called a dielectric). when you first apply a voltage to the leads, electrons start to "pile" up on one plate and leave the other. This continues until the voltage difference between the plates equals the applied voltage. while this is happening, current is flowing in the wires attached to the capacitor. If you now switch the polarity of the voltage to the capacitor, the electrons will start to flow through the wire from the "full" plate to the "empty" one. You will measure an current flow in the wires in the opposite direction.

So now consider what happens if you switch polarity before the capacitor reaches capacity? The flow of electron reverses before stopping. If you switch fast enough, like with a high enough frequency AC, you see a constant AC current in the wires even though no electrons cross the insulated gap between the plates.

Higher capacitance capacitors allow this to work with lower frequencies. Thus by choosing the right value of capacitor, you can select between frequencies above and below a certain point (to with a certain degree. There is no sharp cut off point dividing frequencies, it is more a drop off frequency decreases.

 

 

 

 

Is a variable capacitor what would be used to get a radio wave to go to the correct channel?

 

 

 

It takes more than just the capacitor for the whole tuning circuit, but yes the variable capacitor is what is used to select what channel you are listening to. ( basically by selecting which frequency of all the radio waves out there that your radio circuits will pass on.) And is this the component of the circuit that would allow you to change entities such as brightness, speed of motor, etc?

There are a few different methods to do this, but the all involve selectively choosing frequencies

Dimming lights or controlling the speed of motors traditionally have been done with rheostats or potentiometers (which are both names for variable resistors), But a more energy efficient method( which only works for AC) is to use an Silicon Controlled Rectifier (SCR)circuit.

 

 

 

 

I really want to understand technology (various inventions) better, and I figure this type of stuff is a good place to start, so thanks for your help!

 

 

 

 

You really need to start with the basics of current flow, then work your way up to resistors and Ohm's law, Voltage dividers, parallel circuits, etc. before delving into the more complex areas.

Edited August 31, 2016 by Janus

[joe0311]

Thanks again for your replies! Some of this is over my head, but I can tell you guys definitely know what you are talking about! Yeah I want to start with the basics so I can get a better understanding. Do you guys know any books that would be a good starting guide for someone who wants to understand how technology such as telephones, radio, circuit boards, television, computers, etc actually work? Ideally, I'm looking for a book that could tell me descriptive details like you guys did (not a book that's overly vague), but not in overly technical jargon and I'm not interested in doing a bunch of the math (since this isn't my major). So describing the mathematical laws is fine, but I don't really want a book that's heavy on equations to test students. Not overly wordy like most textbooks have a tendency to be (they have to 'challenge' the students); concise and to the point like you guys have been. It could be a good book, a good youtube channel, whatever. So basically something that would give someone a thorough understanding of how these things work, but keeping in mind that the reader never has to build any of it (I don't want to build them I just don't like using all these things every day and having no clue how they work!) Thanks again!

Edited September 1, 2016 by joe0311

[Sensei]

If you don't know, and don't want to know math, you really won't understand how these things work..

How to explain somebody who does not want to know math f.e. nonlinear electronic element? You probably don't even understand what it means..

Sensible book would show graph, with one parameter in X axis, and other parameter on Y axis. With equation allowing to get such function as on graph.

 

I would suggest getting breadboard,

https://en.wikipedia.org/wiki/Breadboard

760 pins unit cost me less than $2.

With multimeter. The cheapest one $7.

With range of various electronic elements to plug to breadboard.

And battery.

You should see on your own eyes what influence has plugging some element in circuit (in breadboard) on voltmeter, ammeter, wattmeter.

How resistance changes with various resistors, how it changes with variable resistor while moving potentiometer. etc etc.

 

Making LED light dimmer on breadboard would take less time than writing this post..

Edited September 1, 2016 by Sensei

[Sriman Dutta]

Example of complex circuit.......(I think) a dynamo connected to a resistance through a step-up transformer.

Moreover, for your information joe, electricity can only be transported through a circuit. Electricity is the major form of energy by which we can do almost all kinds of work by converting it to other forms of energy. (the law of conservation of energy)

 

But, wait a circuit is not so cool.....Resistance will dissipate a lot of energy.

Total energy dissipated it time t through a circuit of resistance R and current being I = I^2Rt

[wayne_m]

I understand this poster's request and situation completely.
I, too, like knowing how things work, without having to slog through mounds of math. I want to understand the concept, and often have no desire to build the object in question, so do not anticipate having the need to understand the math involved.

It may be that because I do understand the math behind most things, even if I'm not willing to go through all of the work of crunching the numbers, that I find these things fascinating.
I've explored a lot of different disciplines, and worked out a design for a chip that can combine electronics, physics, and chemistry to produce gasoline out of thin air and electricity. (Works better with liquid water and CO2 feedstock.) But it isn't something I would ever try to build: It would be quite expensive to produce, and assuming perfect energy efficiency, would only produce roughly a gallon of gasoline per week per square meter of solar power. (and grid electricity would cost me half-again as much as just buying it at the pump.) What with the time and materials, even "free" gasoline at that rate would take me a couple dozen years to recover my investment. Since there are so many factors where efficiency suffers, I could expect a gallon or two (at best!) per year per square meter of solar power. Not worth the time to build, but fun and educational to design. Granted, I did have to do some math, but not as much as I would have needed if I were actually trying to build one.
So I don't really need to know how to calculate a Henry is to know how a tank circuit works. All I really have to have are the concepts of capacitance and inductance. Maybe someday I would learn enough, and get curious enough to investigate the interactions that make a signal radiate more from the side of an antenna with the director near it, and/or away from the reflector element, but if all I want to know is how the old RCA in the attic works, I don't need any of that.

Keep asking questions, Joe. It's one of the best ways to learn.
I've found that the best way to learn anything, though, is to teach it to someone else. Teach it to your little sister. Or your cat. The point is that teaching a subject will show you the areas where you are weakest, and have the most to learn.

Edited September 23, 2016 by wayne_m

[Sriman Dutta]

I agree with you wayne_m. Teaching is the best way of learning.