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Geek Culture / I need help with electronic circuits

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jasonhtml
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Posted: 28th Jun 2005 11:48
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Hello, For a while now, i have been making electronic circuits on and off just as a small hobby. Well, in the last 2 months i have been designing my own circuits, some working, some not.

Here are my many problems...

1. About a month ago, i learned that the electrons flowed from the - terminal to the + terminal(i always thought it went from + to -). i thought that this might have been the problem why some of my circuits weren't working... But, if i connect the black wire(from - battery terminal) to the Collector and Base of a transistor, the LED connected to the Emitter doesn't turn on. But, isn't the current flow from the - terminal supposed to trigger the Base???

2. WHAT THE HECK IS GROUND!?(for example in a 555 timer ic chip) Reference to ground by many books and websites has made me angry because none explain EXACTLY what it is and how its used.

3. What does a transformer do? i've looked at many sources and they seem sorta vague. how i understand it is that they force current to flow. is this true?


P.S. No offense, if you're not an expert or don't completely know the answers to my questions, please don't respond. I'm sorry if this sounds mean, it's just that i have become very frustrated and confused.

P.S.2. More questions may follow...

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jasonhtml
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Posted: 28th Jun 2005 12:02
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i still dont get it...

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jasonhtml
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Posted: 28th Jun 2005 12:12
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where does it go then, for example on a circuit board... so what ur saying is it just goes *POOF* into thin air

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Briere
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Posted: 28th Jun 2005 12:12 Edited at: 28th Jun 2005 12:14
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When wiring homes the ground wire is often connected to the water pump.


And rubber shoes wont do jack squat when working with transformers and high voltage circuits

The ground wire makes a low resistance path to the ground should a leak or fault occur. Electricity flows in every direction, so by adding a ground wire, your essentially taking away from the potential damage that could occur by removing that electricity that travels down the ground wire. The ground wire should never be connected to neutral or hot wires!!! EVER!!!

and i didnt get too far into the big electronics such as transformers and stuff too much, but , correct me if im wrong, transformers reduce the voltage to that it is usable in homes and buildings.

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jasonhtml
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Posted: 28th Jun 2005 12:13
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but, in this circuit digram i have... the GND pin on a 555 timer ic is connected to the - terminal... not a water pump or earth...

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Briere
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Posted: 28th Jun 2005 12:16 Edited at: 28th Jun 2005 12:16
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It would be wise to follow the instructions, I just took an audio electronics class 2 years ago

I was speaking about house wiring.

The ground wire is a path of low resistance, your body is a path of high resistance. More electricity will be diverted to the ground wire than to your body should an accident happen.

check my above post i edited it.

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TKF15H
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Posted: 28th Jun 2005 13:03 Edited at: 28th Jun 2005 13:04
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in the case of your 555 timer, the ground is the negative pole of your battery. Some projects require the - and ground wire (literaly a wire that goes into the ground, preferably by connecting to a metal water pipe). Often crystal diode radios require this.
Do you know what your transistor is (NPN/PNP)? Really basic question but I have to make sure.
And different transistors have different thresholds so you may need a higher voltage for your LED to turn on.
A transformer reduces current and increases voltage (or the other way around, depending on how you hook it up) if I remember correctly. It's like gears in a car: higher gears go faster but lower gears are stronger.
Also, it requires the input to be AC, and it's output will be DC.

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jasonhtml
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Posted: 29th Jun 2005 00:04
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ok, im starting to get this now...

btw, my transistor is NPN. but, whats strange is that when the Base and Collector are connected to the + terminal, it works....

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Rob K
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Posted: 29th Jun 2005 00:30
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Ground (GND) or Earth, is simply the 0v part of your power supply. The Ground connection acts as a reference for all the other voltages, ie. it defines what 0 volts is.

If you are using a positive-only DC supply (ie. -ve input = 0 volts, +ve input = 5 volts for example), GND just means connect the wire to the -ve terminal. On some DC supplies, you may have three terminals, one for the -ve voltage, one for ground (usually coloured black or green), and one for the +ve voltage.

If you are using two or more power supplies in the same project, you need to have a common ground. Usually this means connecting the two -ve terminals together.

NPN transistors are fairly simple devices. The current flowing into the base determines how big the difference in voltage between the collector and emitter is. When there is no current flowing into the base (ie. it is at 0v), the transistor does not conduct, and so the circuit will act as if there was a big resistor connected between the collector and the emitter. When there is a current flowing into the base (usually 1.1v is sufficient to fully turn it on), there is no voltage drop between the collector and the emitter (ie. they will both be at the same voltage)

In your project, when you connect the base to the +ve terminal, it turns the transistor on, so there is no voltage drop between the collector and emitter. Since the collector is connected to the +ve terminal, the emitter will be at the same voltage as the +ve terminal.


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pizzaman
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Posted: 29th Jun 2005 00:46
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Just thought I'd clear question one up for you. Electrons do flow from negative to positive, however when working with any electrical equipment its assumed that electricity flows from positive to negative. So basically forget that electrons flow from negative to positive when working with electrical equipment.

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jasonhtml
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Posted: 29th Jun 2005 06:12 Edited at: 29th Jun 2005 06:15
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ok, thx, that pretty much clears it all up except i have one more question related to my 3rd question:

can a transformer be used to force current to flow in a wire? just curious... and if it cant, is there a way to do this without connecting the wire to another power source. because, what i am doing is trying to make a circuit that forces current to go through 2 wires:

W1 = Wire 1
W2 = Wire 2
Also, IGNORE THE PERIODS
..____________________________
..|..............................|....................|
-----..........................| W1..............| W2
.---..........................<....................<
..|..............................>....................>
..|............................<....................<
..|_______________|__________|

the problem is that wire 1 has high a high resistance load while wire 2 has a low resistance load... but the electrons take the lowest resistance path. is there any way to force the electrons to go through both wires? and i thought about putting a resistor on wire 2, but i wouldnt know how much to match wire 1 because wire 1 has a variable load resistance.

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jasonhtml
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Posted: 16th Jul 2005 09:37
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plz help.... someone??

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TKF15H
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Posted: 16th Jul 2005 10:09
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Can't you just connect them in series rather than parallel?

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Drew Cameron
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Posted: 16th Jul 2005 17:47
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Quote: "the LED connected to the Emitter doesn't turn on."


Is the LED the right way around?


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Dodo
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Posted: 16th Jul 2005 18:20
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The electrons will go both ways, providing you don't provide no resitsance and lots of resistance(a short circuit). What happens at a junction, is that current is split between the two wires. If one wire has more resistance than the other, the current is still split, but it is not split equally.
Also, you can't use a transistor to force current to go in both directions, because:
i) current already does that
ii) a transistor is just an electronic switch

Part of solving the problem is actually noticing that the problem is there in the first place

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Drew Cameron
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Posted: 16th Jul 2005 20:03 Edited at: 16th Jul 2005 20:04
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I remember that a transformer gives the electricy very high voltage and low current so it is better suited to travelling long distances. (Step up transformer)


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Dave J
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Posted: 16th Jul 2005 20:14
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I'd just like to point out that a transformer is not a transistor.

Rob explained what a transistor is quite well, however, a transformer will simply convert a high voltage to a low voltage whilst increasing a low current to a high current, or vice versa. These are often used in power lines because the resistance in the wires are fairly high (it would be too expensive to provide all those kilometers of wires with a material that's a better conducter of electricity). Because a high current will result in a greater loss of power (P = I^2 x R), a lower current (and subsequentally a higher voltage) is used to transport power from the power station across the power lines, this is done with a step-up transformer converting to a higher voltage (around 500kV for a reasonably sized city) and then at each houses end, a step-down transformer is used to convert the voltage back down to 250V.

Note: A step-down transformer isn't actually used at every single house, instead, there's approximately 1 per street, so there is still a degree of power loss as the high current travels from the transformer to each house (and obviously, if your house is the furthest away, you'll receive the least power).


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Drew Cameron
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Posted: 16th Jul 2005 20:17
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Yeah, what I said!


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Dave J
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Posted: 16th Jul 2005 21:52
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Yes, you posted whilst I was typing out my long-winded explanation and so I was not aware of it until I had already posted.


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Coding Fodder
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Posted: 17th Jul 2005 02:25
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Ok I Will try to explain everything you are asking, If I fail please ask for clarification.

1. LED's (light emmiting diode) only allow current to flow in one direction. (assuming you knew that) but they can't handle much current. Always place at least a hundred ohm resistor in series with them. You may be simply burning them out and that is why they don't light.

2. Ground, other folk covered this pretty well, but it is simply a common terminal to neutralize charge. That is why we stick ten foot copper poles into the "ground" out side our houses. The earth provides and excellent place to send extra charge. as was mentioned the negative side of your power source is usually tied to ground. for most circuits there is no need to plug in to the earth, it just usually means negative.

3. Transformers DO NOT WORK in DC circuits. They (as has been said) simply step up or down the voltage. They do not "force" electrons to flow either.

4. For your parallel resistances.. They should operate independantly of one another unless you exceed the amperage output of your power source. It would be helpful to know what the loads are and what your power source is.

I am happy to help with any more questions you may have. I don't get to use my degree that often so it is fun for me.

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jasonhtml
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Posted: 17th Jul 2005 07:04 Edited at: 17th Jul 2005 07:09
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omg, sorry if im being harsh, but:

1. there are no LEDs in the ciruit, the squigly lines stand for LOADS or resistors(a LOAD is the total resistance of a circuit or part of a circuit), the symbol for LED is a squigly line with a circle around it

2. i know the difference between a transistor and a transformer!

3. Coding Fodder's #3 helped and answered my question, while everyone elses did not...


ok, so a transformer cant seperate the current in my diagram, then what can? i dont want to use two power sources and i cant put them into a series...

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Drew Cameron
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Posted: 17th Jul 2005 07:11 Edited at: 17th Jul 2005 07:14
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Quote: " there are no LEDs in the ciruit"


Sorry, but I read this...

Quote: "..the LED connected to the Emitter doesn't turn on..."


My mistake, hope you get your circuit working now!


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Coding Fodder
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Posted: 17th Jul 2005 07:34
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Once agian it would be helpful to know what you are trying to do. But if you know ohm's law I=V/R Where "I" is the current or amperage "V" is the Voltage and "R" is the resistance.

If your power source is a 5V DC source then there will be a 5V potential across both branches of the circuit. According to Ohm's Law the amount of current depends only on the supplied voltage and the resistance of that particular branch.

What I am trying to say is that having the two branches in parallel is not what is causing your trouble. (whatever it is) They are operationally independant.

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TKF15H
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Posted: 17th Jul 2005 08:02
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Quote: "What I am trying to say is that having the two branches in parallel is not what is causing your trouble. (whatever it is) They are operationally independant."

not really. If one of the branches has a lower resistance, more current will flow throught that one than the other. It's like connecting a light bulb to a battery, and shorting it.

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Coding Fodder
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Yes Really!! Hey nice fish by the way. Yes more current will flow through a lower resistance path but it will not change the amount of current in the first path. The voltage source simply puts out more current to handle both.

The only time there is trouble is if the power supply can't keep up with the demands of both. as you suggested a direct short is a good way to do this. The chemicals in the battery can only react so fast. But upto that limit they operate as completely different ciruits.

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jasonhtml
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Posted: 20th Jul 2005 00:12
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so, basiclly, one side of the circuit has WAY to much resistance compared to the the other side... but, is there ANY possible way to FORCE it to split to equal voltages being supplied to each side so that the lower resistance one doesn't short out the higher resistance one? (btw, as i said earlier, i dont want to use 2 power sources)

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TKF15H
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Nope, I don't think there is. As Coding Fodder explained, the reason one side is not getting power is because the battery can't maintain a steady current for both.
Let's call the side that's hogging all the power A, and the side that isn't getting any B.
I'm thinking that putting a transistor on A, so that when A gets no power, it will lower the amount of current passing to B. With less current going through B, more goes to A, so it will balance out. I haven't done anything with electronics for a few years, I don't know if I'm making any sense.

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jasonhtml
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Posted: 20th Jul 2005 22:45
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that sounds like an idea, but... lets say that it did work... if the section A is processing something and the power cuts and then goes back on because of the transistor, will that cut cause it to mess up?

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TKF15H
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Posted: 21st Jul 2005 06:37
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Shouldn't mess up, but then again, I have no idea what I'm talking about.

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jasonhtml
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Posted: 23rd Jul 2005 02:05
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o...

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Class I Coder
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Posted: 25th Jul 2005 23:30
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Coding Fodder knows what he is talking about.

If you are interested in learning, look up 'maximum power transfer'. It basically states that you only get max power transfer when the output impedance (in this case impedance = resistance)matches the input impedance (resistance of the load). If you apply too high a load for a battery (in this case a secondary cell) then gas builds up around the anode, cutting down on the surface area that is in contact with the chemical. This increases its resistance, decreasing current.

'Ground' is just the return path that current takes to get back to the source or power supply.

There is only one form of current - electron. It flows from negative to positive. However, in the early days of electrical engineering its direction of flow wasn't known. This led to academic papers being published which were hard to follow. So in 1910-1911 (if memory serves) a convention was held and it was decided that for academic purposes current flowed from positive to negative. This current is called - surprisingly - 'conventional current'. However Americans,being Americans, ignored the convention. So American textbooks show current flowing - to +, while European and British textbooks show it as + to -.

As for power cuts when something is being 'processed' - what and how are you processing? More info needed.

If you need any help, just ask. I'm back from Uni for the next month...

BTW try downloading MultiSim/Spice/PSpice. It allows you to design and test your circuits in the virtual world using your PC. This should save you from blowing any diodes/trannies/resistors etc.
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