Ground the same as negative charge?

In all the Arduino projects I see leds being connected to a output pin and the GDN(ground)

But isn’t the ground a charge of 0 volts?
If it was, then I wouldnt even have to connect the GND.
I hope someone can explain!

It is difficult to answer your questions without first giving you a background in electronics :wink:

First, “voltage” and “charge” are not the same thing. So your question really should be “Isn’t the ground a voltage of 0 volts?”

The answer is, yes, it is. But do not think of “0 volts” as being the ground we walk on with respect to gravity. The number “0 volts” is an arbitrary number we assign to a point in a circuit because, well, it doesn’t hurt and it keeps all the other numbers small.

What really does the work is electrons FLOWING (i.e., current). If you tie one end of an LED to a pin and the other end is tied to nothing, no current can flow so nothing is going to happen. By connecting the other side to “0 volts” you are allowing a closed path (i.e., a circuit) for electrons to flow: from the pin, to the LED, to 0V, back to the same 0V potential of the Arduino, and that’s a closed path (in fact the path is more complicated because it starts at the power supply).

Ok thank you very much!

This thing seems to confuse a lot of people. Ruggedcircuits explained it very well.

Remember that ground can be anything you choose to be ground.

Usually most people choose negative to be their circuit ground and that makes it easier to read diagrams. Usually ground is synonymous with 0V for simplicity sake.

If you see that some point is at say +3V in a common circuits that means that between that point and ground is +3V, or it is 3 volts relative to ground or 0V.

The reality is that everything is relative. So what you define as 0V can actually be some much higher potential or state of charge than say the earth for example. Try not to think about charge and physics too much when working with signals and topologies because that can confuse the issue a bit.

Hi,
If you want it explained but with a few pictures then try:-
http://www.thebox.myzen.co.uk/Tutorial/Power.html