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Grounding Question

Discussion in 'General Electronics Discussion' started by Crogdor, Feb 7, 2014.

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  1. Crogdor

    Crogdor

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    Jun 7, 2013
    Hi, I have a newbie question about grounding.

    I bought a 5M LED strip that uses WS2812b drivers to control the LEDs. It's for use with an Arduino UNO controller.

    The strip uses a 3 wire setup: VCC, GND, and Data. If I connect VCC and GND to the power supply, and Data to the Arduino controller, the lights just go white and flicker with some minor color variations. Yet if I do the same thing, but additionally connect the GND of the LED strip to a GND pin on the Arduino, then it works.

    So why isn't it good enough that the strip itself is already grounded? Why do I also have to connect the ground wire to my Arduino? It seems weird to have to connect ground to two places for it to work.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The power supply to the arduino and the power supply to the lights need a common ground or the voltage on the data pin refers to nothing and the WS2812 chips can't make any sense of it.
     
  3. donkey

    donkey

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    Feb 26, 2011
    I know I am going to get corrected here but its my way of looking at the data lines.
    a common ground is needed for the 0 and 1's. it needs a point that is 0 that is ground then when a signal goes through it understands that's a 1.
    now the reason you need a common ground is grab 2 batteries and connect a light from the negative of 1 and the positive of the other it won't light, the ground and the positive rail MUST come from the same power source.

    now the easiest way I can think of doing this is connect the 2 grounds together but I know I will be corrected on this for some reason.... maybe
     
  4. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    I know most people use it but please try not to use the word ground for common. It is not the same. Also neither is negative appropriate. In doing so you will confuse yourself when you do come across both and think they are the same. The correct terminology as steve has said is conmon or zero volts. And yes there is no such thing as zero but its the nearest we have.
    Donkey you are correct but just drop the ground thing, unless you are connected to it . The reason is that charge always returns to its maker, and in a PCB trace with a return plane the return current always flows underneath the track that sent it. Its the same for batteries. The batteries that give up some charge needs it back to carry on working. It does this by getting it back from the return charge along the common wire.
    Adam
     
  5. donkey

    donkey

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    Feb 26, 2011
    ground being used so commonly on nearly every schematic I see makes it a hard change. also when the device Crogdor is using has an area labelled ground I find labelling it anything other will confuse the original poster.
    for those that know electronics we know ground can be either a reference point or actually putting a spike in the earth.
    in this case I mention ground as the area on his arduino AND on his driver for the posters own ease of mind. If the area was labelled negative I would have used that reference for the OP so its easier to understand.
    changing terms people are familiar with or not familiar with especially when something is labelled as that will only serve to confuse. we are here to help those that need it, not to baffle new comers and make things hard thus discouraging them from ever trying again
     
  6. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    That's a valid point Donkey, but doesn't make it right. For example I have a power supply on my desk which has a green connector a black connector and a red connector.

    The green connector is Ground and has a ground symbol. What do I call the black connector then? I can't call it Ground because the green connector and the black connector are not joined together electrically.

    Below is an extract from David Bridgen website, this guy was the first man to broadcast TV signal from the Falkland islands after building his own camera and transmitter to record his own wedding. He makes a some points about the misuse of ground and earth, you might find it interesting.

    Earth? Ground?







    I shall be modifying this in the near future. (posted Friday 25th May 2012)

    Never mind, I couldn't be bothered.

    ************************************************************************************************





    In the beginning (as far as radio and electronics is concerned) there was the electric telegraph.

    The basic circuit consisted of three parts connected in series; a battery, an electromagnet and a switch (the “key".) The key would be at one end of the circuit, the electromagnet at the other.

    The key controlled the current through the line and therefore through the electromagnet.

    The system at first used two wires but it was quickly realised that one of them could be replaced by using the Earth as one conductor.



    And then Marconi said, “Let there be radio.”

    An essential part of radio is an antenna and an essential part of early antennas was a connection to the Earth.

    You will have noticed (won’t you?) that both times I mentioned Earth I also used the definite article. Yes; the planet on which we live.

    The ubiquitous, misunderstood and frequently misused ‘ground’ had not yet made its potentially lethal way into our technical jargon.


    It won’t go amiss to say here that, in an electrical/radio/electronics sense, Earth means not just a conductive connection to the planet but a very low resistance connection, and in the case of a.c. a very low impedance connection at all frequencies being considered whether they be 50 or 60Hz or microwaves.


    Older radio receivers needed a connection to Earth to improve antenna efficiency and later, when they became mains operated, in the interests of safety too.


    Eventually someone, somewhere, possibly because they thought it was clever, possibly because of grammatical sloppiness, introduced the word ‘ground.’ (Since its use is confined mainly to the U.S.A. I must make the reasonable assumption that it was there.)

    Which was most unfortunate. It is much less evocative than the original, genuine, accept-no-other, Earth.

    My use of the upper case E should by now have served the purpose of drawing attention to something of paramount importance, so I shall now drop it in deference to convention.



    Use of the word earth, or the less satisfactory ground, was, as long as radios and other items were mains powered, quite unambiguous. The chassis of most, if not all, older radios were connected to earth. Furthermore it was and still is common practice for one side (or pole) of the receiver’s power supply to be connected to its chassis and therefore to earth.

    It was quite usual in the service environment to speak of measuring a voltage within a radio between such and such a point and earth, or ground. Both words being synonymous.

    With the advent of portable battery operated radios (and the development of ferrite rod antennas) the earth connection, at least on those receivers, disappeared. The old habit of referring to the receiver’s chassis as ‘earth’ or ‘ground’ didn’t.

    As a not too successful palliative, the expressions ‘earth ground’ and ‘chassis ground’ were introduced. And there ended synonymity.

    (Think ‘earth earth’ and ‘chassis earth.’)

    What a ridiculous situation. If you need to say "earth ground" or "chassis ground" - and you DO need to in order to convey what you really mean, then why not drop the silly and confusing "ground" and simply say "earth" or "chassis" and, if necessary, say whether or not the chassis is, or should be, earthed.

    So common is the use of the word "ground" - it tumbles out of peoples mouths like a ritual - without stating what is meant, that I suspect that it is either taught or simply copied from other people who are imprecise with their terminology. In the former case the teachers need their heads banging together.

    We even have people talking about the 'positive of a battery and its "ground". Stupid, unthinking, and totally wrong and misleading.



    Even more unfortunate is the fact that most people who use ‘ground’ don’t bother to state which ‘ground’ they mean, if, indeed, they understand the difference anyway (and I'm quite sure that many of them don't). It’s just part of the jargon which people use unthinkingly.

    And that really is potentially fatal.

    Unthinkingly. Yes, very much so. I well remember in one of Racal’s technical handbooks, one pertaining to an airborne radio, that a certain pin on one of its connectors was the ‘earth’ pin. Earth? In an aircraft? Just how sloppy/stupid can people be?






    There is equal confusion between the diagrammatic representations of earth and chassis. The former being grouped horizontal lines whose lengths diminish from top to bottom. The latter is one horizontal line with short diagonal lines hanging from beneath it. Check out the very earliest circuit diagrams of radios.

    Look at most semiconductor manufacturer’s data sheets or application notes. They are littered with earth symbols.

    Some circuit-drawing programs also insist on appending earth symbols to a power supply’s common line.







    Which brings me to another point.


    Whenever I draw a circuit diagram or whenever I speak about a circuit I avoid as far as is possible the word ground.

    I will sometimes, but not always, use the chassis symbol in a diagram. In many cases it is simply not necessary.

    I usually label the circuit/power supply common connection as 0V. If the application is a road vehicle I will label it chassis.
    In a written or verbal description I say 0V or chassis.



    Some people don’t understand this, so ingrained is their habit of using ‘ground’ or ‘earth.’ But I stick to my guns. I would rather someone ask than indulge them in their common and imprecise jargon.

    One of the problems is that people are taught by other people who know no difference (or better) and it is not until much later that they might encounter someone who deliberately or otherwise challenges their cherished beliefs.

    I can not and will not accept fatuous arguments supporting something because "lots of people have done it like this for a long time." All that does is preserve and propogate myths and misunderstandings.

    Old habits, particularly bad ones, die hard. It is nigh on impossible to get someone to even contemplate that they just might be wrong.

    R.m.s. power anyone?
     
  7. davenn

    davenn Moderator

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    Sep 5, 2009

    is that on the mains input or the DC output ??

    if input .... the black is neutral ( for places other than the USA and a couple of others) under the old colour code

    If output .... the black is 0V or negative

    but surely you should know that ?? ;)

    Dave
     
  8. donkey

    donkey

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    Feb 26, 2011
    I made a project once, it was a very simple led and motor design for my nephew to play with.
    all the wires made sense to me. My brother however got confused due to the fact they were all blue.
    so I labelled them start to finish showing where everything got plugged in.
    now I did not put on Ground or negative or positive.... I simply gave him a 9volt connector and labelled where they connected to.he understood the concept.
    the basics of electricity is explained in a water analogy and that's easy to understand for a lot of people.
    I find when people ask me a simple question giving a simple answer is the best policy not correcting them on a phrase that they see labelled somewhere and use that. once again I am trying to help the OP not confuse him by giving him more information than he needs.
    If Crogdor has had success than I feel happy. If I spent all this time explaining the reasoning for ground to be an incorrect term then he would still be confused and have something more to confuse him.
    anyway that's all I am posting on this subject
     
  9. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Good job it was not mains operated and you asked him to ground the metal work for safety reasons. He then connected the wire to zero volts. Get the point now?
     
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