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A ground / negative connection question

Discussion in 'General Electronics Discussion' started by SparkyCal, Mar 16, 2020.

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  1. SparkyCal


    Mar 11, 2020
    Hi folks:

    I am getting reacquainted with electronics. I have always had an interest in it, but after taking electronics in high school, I allowed it to fade into the background.

    I am now 58 years old and trying to rediscover it. Having the internet and access to relative;ly cheap components and tools, as well as Adruino , has it made it all the more alluring. I truly appreciate the time and expertise people with more knowledge are willing to contribute. So thank-you upfront!

    Here is my question:

    I can recall when building a basic circuit (for example a light and a battery) that a loop must be created in order for it to work. So the negative terminal always ends up looping back to the positive terminal, or vica versa.

    But I am confused about sending things to "ground" . I always thought any component that had a positive charge connected to it, must find it's way to the negative terminal in some way, in order for that loop to complete and the circuit to succeed.

    But when sending things to ground, what does that mean? Does it mean that a component could be connected to a ground terminal rather than a negative lead (source), and if so, why?

    I have watched so many Youtube videos on this now, but I have not found any that make it clear- to me anyway.

  2. davenn

    davenn Moderator

    Sep 5, 2009

    hi ya
    Welcome to EP :)

    I have moved your thread to a better section of the forum since you have a query in it

    hopefully it will get more vies here and an answer or two

  3. bertus


    Nov 8, 2019
  4. Martaine2005


    May 12, 2015
    I think a simple explanation to begin with is more useful.
    Think of a battery, it has positive and negative terminals.
    Your ‘loop’ is not a correct explanation. If you ‘loop’ or connect them together, you have a short circuit. That is not good and things go ‘bang’!.
    Instead we have resistance in the form of a bulb or motor etc. This would generally be called a ‘load’. This ‘load’ is connected between the positive and negative terminals of your power source (battery).
    Now we have a circuit. That is the correct saying for your ‘loop’.

    Cannonball likes this.
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    "Ground" is nothing but an electric potential defined for reference. Named so because in many cases it is connected to the physical ground (earth) you are standing on. Often the terms ground, earth or common are used with the same meaning, although it is good engineering practice to keep them separate as they can have different uses.
    Whether ground is connected to a positive terminal or a negative terminal is also only a matter of convention, but it is fairly common to use the moste negative potential as reference and hence name it ground.

    Confusing, isn't it?

    Let's try to sort things out:
    What is voltage? Voltage is the difference between two electric potentials. There is no absolute reference (no "0" potential). You always measure voltage between two points. Your battery is a simple example. It has two poles, a + and a -. Let's sa you have a 9 V block. Surely the voltage between the two poles is 9 V (or whatever is left after discharging the battery). Now if you connect two batteries in series, connecting + of one battery to - of the second battery, the total voltage is 18 V, but still each battery has only 9 V.
    Where does ground come into play? It is common practice to refer all voltages in a circuit to a reference potential (often called reference voltage, although this is a misnomer as I stated above). This reference potential can be chosen arbitrarily. In the example of the two stacked batteries you have 3 choices (actually many more but that leads too far here):
    1. Use the most negative potential (- of battery 1) as ground. Battery 1 is then at 9 V above ground, battery 2 at 18 V above ground.
    2. Use the center connection as ground. - of battery 1 is then at -9 V with reference to ground, + of battery 2 is a t +9 V with reference to ground.
    3 Use the most positive potential (+ of battery 2) as ground. - of battery 2 is then at -9 V with reference to ground, - of batteryy 1 is at -18 V with reference to ground.
    Which version you chose is up to you. Only be consistent: within one circuit there should always be only one ground potential.

    This setup implies that ground is the most negative potential. In your case it would be the same as the battery's "-". So the component is not "connected to a ground terminal rather than a negative lead", but the negative lead of the source (battery) is the same as ground. That closes the loop you are looking for.
    Martaine2005 likes this.
  6. Martaine2005


    May 12, 2015
    And I forgot..
    Sending to ground. This is much more complicated but in your battery scenario means connecting to the battery negative.
    Electrical items that are ‘grounded’ or ‘earthed’ are really quite different. In the world outside of batteries and double insulated supplies, an earth or ground may be required. This would mean that the negative terminal is also connected to earth.
    But keeping it simple, what and why is your question?

  7. SparkyCal


    Mar 11, 2020
    Thank-you and sorry.
  8. SparkyCal


    Mar 11, 2020
    This is helping. Thank-you.

    What and why is my question . The why is because I am trying not to get confused between the negative lead and what it does, and ground.

    Having read the replies, let me see if this is true:

    1. Ground can be used as a reference point to measure voltage that is running from point A to ground. So if I have a breadboard, and I have a connection on that board secured to the ground terminal on my power supply, I can hook up a positive probe to any component in my circuit (let's say a resistor), and hook the other probe up to the ground ( as just described), and measure the voltage. running through that resistor and its resistance.

    2. Ground may or may not be used as part of a circuit. Now here is where I am confused. So, let's take a simple light hooked up to a 9 volt power supply. I can either hook it up by running the light (load) to the positive probe and negative probes. Or the positive and ground probes, and still achieve the same result?

    Please bear with me. I'm trying to get grounded with this ;-)
  9. Martaine2005


    May 12, 2015
    This was meant to read that they are connected together downstream and not at the appliance.

  10. Martaine2005


    May 12, 2015
    Erm, I am confused by #1.
    #2 no.
    If #2 is isolated from ground (earth) no potential exists.
    If you connect to negative, then your bulb will light.

  11. SparkyCal


    Mar 11, 2020
    I hope I am posting this question in the right forum.

    Can anyone look at the circuit diagram shown at 1:11 in the video referenced. I need to know the following:

    When building this circuit, when it shows the three connections at the bottom of the diagram as going to GND (ground), does that mean, practically speaking that I would connect those leads to the negative terminal on my breadboard, or to the ground wire coming from my power supply?

    Theoretically, I beleive I understand the concept and importance of ground, but practically, within a circuit, I am confused by when to connect to negative terminal vs, ground.

    Here is the youtube link tot he circuit. It is at point 1:11
  12. Audioguru


    Sep 24, 2016
    The grounds in that circuit are common connections of the three at the bottom of the schematic, the connection of the 0.1uF capacitor at pin 4 and pin 8 of the NE555 and the 0V of the 5V power supply. They are all connected together and the letters "GND" to avoid showing wires all over the schematic connecting them. They should all be connected close together (on a pcb).

    The antique NE555 is a high current old TTL design. The resistance, inductance and capacitance of the rows of contacts and long wires all over the place on a solderless breadboard cause trouble with it. The datasheet of the more modern ICM7555 low power Cmos 555 IC shows that the old NE555 conducts a power supply current pulse of 400mA (!) each time the output switches which a solderless breadboard has trouble with. Your power supply or battery also might have trouble with the 400mA pulses.
  13. SparkyCal


    Mar 11, 2020
    Hi Audioguru and thanks. i was not necessarily going to use this circuit. I am only trying to understand whether the GND designations should be connected to a negative lead or the ground terminal. So, are you saying that the connections of the 0.1uF capacitor at pin 4 and pin 8 of the NE555 and the 0V of the 5V power supply should all be connected to a negative lead, or to the ground lead? that;'s what i am trying to understand. Thank-you

    i apologize. I know my wording sounds like I am going to build this circuit. I'm not. I am only citing it to try to understand
    davenn likes this.
  14. Nanren888


    Nov 8, 2015
    Yes. The power supply is connected to +5 and GND (0volts, power supply negative).
    There are two +5 connections, which should go together and to the supply positive.
    There are four places to connect together to GND, which goes to the supply ground (-ve).
    The last one is the power supply bypass capacitor, between +5 and GND.
    This is supposed to help with current spikes like those introduced above, though maybe not as big as those suggested might occur.
  15. SparkyCal


    Mar 11, 2020
  16. Minder


    Apr 24, 2015
    The schematic used the correct symbols, unlike the Maxim tech sheet that used the earth GND symbol, often used in error, in place of power Common.

    Attached Files:

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