DIY Variable DC Power Supply Help

Discussion in 'The Projects Forum' started by MrMobss, Oct 14, 2014.

  1. MrMobss

    Thread Starter New Member

    Oct 14, 2014
    Hello, i just joined for my burning question to be answered as it seems that there are many great minds here on this forum. Right to the point, I am trying to follow and create this instructable:

    What I cannot figure out is just one thing about the fairly simple schematic:

    It is the ground or rather the common ground(?) symbol. I have read countless threads and all the answers seem to be that the symbol is a point of reference, or it is the return point to the negative terminal of the source. Of course these answers do not answer specifically to me. So my question is What do I do when i see this symbol? Do i tie all that have the same symbol and or connect to the negative terminal of the power source?
    Please and thanks.
  2. JDT

    Well-Known Member

    Feb 12, 2009
    The Earth symbol that is used here is not really the correct symbol to use.
    It is supposed to be the negative reference point and I assume it is connected to the negative supply input.

    A "0V" symbol (small horizontal line with text) might be better. The earth symbol used normally shows that it is actually connected to the earth but that might not be true here.

    There is a lot wrong wit this circuit. One thing I notice is that the two transistors are drawn as PNP types but need to be NPN.

    I assume the "Positive connector" and "Negative connector " are the output terminals. Never seen pictures used in circuit diagrams before!
  3. MrMobss

    Thread Starter New Member

    Oct 14, 2014
    Yes the output terminals is the positive and negative connectors. I believe it is suppose to be for newbies like me? I don't really come from an engineering background. So I connect the points to the negative input terminal?
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Think of the GND symbol as meaning "connect me to all other similar symbols with a short and fat wire". In this context, the useage has nothing to do with "connect me to the cold water pipe"...

    I agree that most of the stuff posted on Instructables, while pretty to look at, is usually pretty awful...
  5. MrMobss

    Thread Starter New Member

    Oct 14, 2014
    That helped thanks!
  6. MaxHeadRoom


    Jul 18, 2013
    Unfortunately you will constantly come across the common mistake of wrongly using the Earth ground symbol as the Power common terminal instead of the correct one, even the 'The Art of Electronics' uses it throughout its 1200 pages and does not even describe the symbol, or any other, (not that I can find, anyway).
    It ends up completely eliminating the original definition.