Relatively new, looking for some basic answers.

[Dahboo]

Hey guys,

I'm a bit of a n00b (Okay, more than just a bit) when it comes to electronics as far as circuitry. I've been involved with computers on a hobby level since I began teaching myself at age 8, but now I'm interested in getting involved in circuitry.

I have been searching the internet for a good explanation on transistors, and more specifically, how they amplify signals or current. I have been able to find many great explanations that explain how to do it using transistors (ie. how to wire a circuit that does it), but I have yet to find an explanation that covers what is actually occuring. I am not able to read a schematic very well as of yet, and I'm still picking up the basic concepts, so I ask that you use easy-to-understand language with me. My first question:

Question #1
How does a transistor amplify current?
My understanding of a transistor so far is this: In an audio amplifier for example, a low power signal from a microphone is sent to the base pin of the Transistor, varying the conductivity, and allowing the Transistor to duplicate the same variances of the low power signal onto the much higher signal flowing from the emitter to the collecter.

If that is incorrect, please correct me, as I am eager to learn! Now, the problem I have is that my current understanding of transitor amplification only allows for a small signal influencing a larger, more powerful one. How, then, does the Darlington Pair work? Is a transistor able to increase the power of a single signal without the need for a second, more powerful signal?

Question #2 (More of a theoretical question)
In a Crystal Radio, no power is needed because the radio power requirements are low enough that it can draw power from the signal. Is there any way to use the same concept of drawing power from a signal, or many signals, and then amplify it to the point where it could power other devices? If so, how would one amplify the power? Transistors?

Thanks alot in advance, everyone! ;D

 

[ante1]

Hi Mike,

Welcome to this forum.

At this place: http://www.ibiblio.org/obp/electricCircuits/
You can download six really good books that give you a start in the electronics field from scratch.

Q#2. If you live near a powerful radiostation / transmitter you might get energy enough to run a very small low power gizmo but it

 

[Dahboo]

Excellent!

Thanks for the information and answer, I'll check it out!

 

[EnigmaOne]

To the issue of powering devices "for free"--because that's really what's being said, here--it can and has been done in the past.

My, now dearly departed, high school electronics teacher (don't ask me how long ago that was) said that he personally knew a man he served in the Navy with, who happened to live out in the South West desert area of the USA (I'm remembering that he told us that it was in the Nevada Desert, but it's been so long ago now).

Seems this guy dug two trenches directly under the power lines that ran across his (very sizable) property. He joined the trenches with a connecting trench, and placed a very long loop of insulated cable into the hide away and covered the whole thing up.
He connected this newly constructed secondary winding, of what amounts to a large transformer, to his house wiring and got the power to run his deep well pump, lighting and appliances for free--for what we were told was something in excess of 15 years.

The utility folks eventually came 'round investigating the source of fluctuating power losses, that had previously defied explanation, but had been narrowed-down to the span of high tension wires crossing his property. He was discovered, given amnesty (because there were, at that time, no laws against what he did), given a free utility transformer and drop, and a job with the company--finding people who were cheating the utility provider (exactly what he had been doing). He had his utility charges deducted from his pay check.

Now...the "event"--as related to us--took place sometime back in the mid-to-late-1940's; and could be nothing more than a good story to tell a bunch of high school kids in freshman-year electronics class...and every ex-Navy guy I've ever known could tell some whoppers.
BUT, I did and do know enough about this teacher to believe that if there is such a thing as being honest to a fault, this man was exactly that. It would be a departure from his "norm" to tell us a lie like that, but I'll leave that one up to you to believe or disbelieve.

In that scenario, it is technically possible (given certain power line configurations), but illegal in just about every jurisdiction I can think of.

Being close to a high power radio transmitter antenna?

Well...
#1 - I'd have some health concerns about living in that kind of environment for an appreciable length of time.
#2 - You could probably parasitically capture enough power to do something useful with if you converted the received signal to DC and stored it in the usual way.
#3 - It's probably also illegal, although I'd love to see a radio station try to prosecute somebody for doing just that.

Anyway...that's just me, chiming in on the subject.

 

[Edude03]

Same Idea as above i build small stuff and i rite software oh and i mostly us linux for programming. how can i interface the 2??

 

[ante1]

Hi Enigma,

I think it is a good story and fully possible too. Why wouldn

 

[steven2]

the trusty transistor, like the led are the results of reverse engineering from crashed alien space craft in 1947, the same year the transister was invented

 

[trigger]

A nice story.,..... it is practical but need big coils for induce enough power to drive home appliances........

 

[MP1]

Nice story. But when he put the cable in a trench and covered it up with dirt (earth), he was putting "Earth Ground" around the cable, which technically was the same as shielding your cable from interference. I can accept that this might not have been a real efficient shield, but to get enough power to run a well pump, lights and appliances? I have to be the skeptic on this one.

MP

 

[ante1]

I think that in the dessert the dry sand or dry earth for that matter will not be much of a shield. As I said a BIG coil should work and the more current the power line carries the more power is induced in the BIG coil! ;D

 

[Kevin Weddle]

A transistor can be thought of as a current amplifier. Because there is multiplication involved, the change in current is greater. That is really what the transistor is about.

 

[Alun]

Believe it or not, if I hold one leg of a super bright white LED and connect other to the radiator in my room it glows very dimly, my body is acting as an antenna and the radiator is acting as a ground. But I don't believe this story as the LED will glow dimly @ <50

 

[EnigmaOne]

I think that in the dessert the dry sand or dry earth for that matter will not be much of a shield. As I said a BIG coil should work and the more current the power line carries the more power is induced in the BIG coil! ;D

In thinking back on this some more (yeah, more than 30 years now), and checking my recollections against those of a couple of other guys who were in the same class with me (my phone bill is going to be high this month); we've been able to piece-together a bit more of a picture of what was said:

The trenching was shallow, because pieces of wood (Maybe it was diagonally staked in place?) were used to hold the cable down to be covered-up. (I totally forgot about that part.)

Power lines that run through that general region now, are on the order of several mega-volt transmission lines, and carry current well in excess of 1000 Amps. I have to think that they certainly weren't light-duty, low-current lines back in the purported era of the story, as told to us. In view of this, I'd wager that the shielding effects of dry ground would only be evident at something below a meter.

The teacher held up his thumb as a size indicator of the cable supposedly used. The significance of this hit me only last night...he had to be talking about something like MMC250 or MMC500 cable, for which I2R-losses wouldn't be a huge factor. (The copper, alone, would be worth some serious money today!)

This guy's property was--evidently--measured in terms of miles, making one helluva secondary winding. One guy remembered a diagram on the blackboard, about this story, that showed a single-direction dimension line in units of "miles" but can't remember how many. (I'd be impressed if he could.)

One guy thinks that the coupled power was DC-stored, and the other guy remembers that the power was used directly. I remember some statement about there being an issue with the voltage induced in the coil.

So...

...I still don't know what to think about it; although I still believe it to be theoretically possible, if not somewhat improbable.

I guess I should start writing some letters to the companies that may have been involved in something like this, if it ever happened.

 

[Kevin Weddle]

Storing DC without the reoccuring charge of the input is not a good method. You are relying on the current from the capacitor solely and the energy stored is not that great. energy=.5CVsquared.

 

[Dahboo]

A transistor can be thought of as a current amplifier. Because there is multiplication involved, the change in current is greater. That is really what the transistor is about.

But does it require a stronger current being applied in order to step up the power of the existing current, or can it only use one power source, and multiply it? If so, can you explain how?

 

[ante1]

Yea, it would be interesting to know! ???

 

[Kevin Weddle]

The transistor uses a low base current to generate a higher current flow from collector to emitter. That's all. It does this because of how it is constructed. I think it is because of the voltage that exists betweeen the collector and emitter. Whenever you get conduction from the base to emitter, it allows for a barreling effect. The electrons that flow between the base and emitter causes a breakdown of the semiconductor. You see the transistor wants to conduct from collector to emitter when you have voltage from collector to emitter. All it needs is a little base current to cause an avalanch effect.

 

[ante1]

Kevin,

The question was:

But does it require a stronger current being applied in order to step up the power of the existing current, or can it only use one power source, and multiply it? If so, can you explain how?
Can you please answer it!