The Truth about Grounding!

[csurban]

I have a friend who is is an acoustical engineer. He deals mostly with telecommunications but knows a great deal about audio and video signal processing in microchips and motherboards. Sooo.... I asked him a question which has bothered me for a long time. Is there really only one ground? Well... He said that any system of electronic circuitry will have one universal ground BUT!!! in a system such as a motherboard, grounding for certain components are isolated from the main ground.

That is, grounding your video or audio output from the N64 to the main power ground as opposed to the provided ground on the N64 A/V pinout DO NOT produce the same effect. Mainly, you get interference when using the main power ground. My friend said that a PCB is layered, as many of you know, and in these layers is a hiarchy of grounding.

It starts with the main power ground (this would be the metal stripping on the side of the PCB or the provided ground for the 1-6 power connector) as level one. This level has the most interference because of the raw power inputed to the board. Then, I suppose there is or is not other layers in between the first layer and the A/V signal layer, which is the one we are concerned with.

Now these layers work through the rule that the pervious grounding layer can access all the layers above it but is isolated from the layers below it. For example, if the power ground is layer one, A/V ground is layer four and and the CPU ground is layer 6, the power ground connects to all the other layers, the A/V layer connects to the CPU but is isolated from the ground, and the CPU layer is isolated to all but itself. SOOO... putting all of this knowledge to use, I corrected a problem with interference I was experiencing.

I arranged my A/V signals in accordance with my second diagram but in doing so, my A/V was grounded and functional but you can see that it has to travel through many layers of grounding which adds interference to the signal IN ADDITION to having direct access to the very raw ground of unregulated battery power via the connection to the metal stripping which adds the battery's own interferience. Now these interferences may seem small even when added up but when you are using an electrical signal to view video at NTSC standards, the interference becomes quite noticible. In my project, vertical lines would mesh in and out of the picture. I was actually seeing the interference!

So I asked my friend about this and received a long answer about grounding and then i wend home and arranged my A/V input in based on diagram one and VOLIA!, no lines! Now what I said may not be entirely accurate because i am merely passing on what I understood from my learned friend. If you know more about this then me and would like to correct my explanation, go right ahead. Even is my whole thory is wrong, I would like to know what is how grounding really works Embarassed

[gannon]

I didn't read your post because it looked like quite the jumbled run on, but ground is always 0V. That's not to say that every circuit needs a ground, if I want 12V flowing though a circuit I can use many multiple voltage references, inluding (0V, 12V), (-6V, 6V), (12V, 24V), etc....
The most common base reference for voltage is 0V (ground) though.

[Krepticor]

ok here is the deal ground is where electrons come from

contrary to popular belief electrons do not flow in the direction where current is positive, electrons having a negative charge

I=dq/dt

that is the change in charge over the change in time or the derivative with respect to time

hence negative charge, negative current, The current we know and love is in actuality the opposite direction of the electron's movement

When one is looking for electrons, they essentially need just a large supply, this interference you speak of is probably just a confusion in the electron's path