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If we do not separate Positive and Negative flow, what is the flow from a 3.3V connection?

A Little more background on why I ask this question and my confusion follows

I have been reading simple circuit design tutorials online, most of these include a battery with two terminals, one positive and one negative, which we connect cables to and eventually complete a circuit.

However as I began to progress, I noticed certain circuits began to have a 3.3V connection - One example would be a GPIO pin(Pin #1) on a Raspberry Pi. If I was to make use of this pin, would this be a Positive or Negative terminal? Perhaps it doesnt matter? or perhaps it is neither?

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The 3.3V connection on a RPi is +3.3 volts, relative to the Pi's Ground. The Pi also has a +5V connection on the I/O header - this is +5V relative to the Pi's ground pins.

In general, any voltage you see mentioned on a circuit is the voltage relative to the circuit's ground. And, in most cases, the term "ground" does not imply a connection to the earth - it is just the point in the circuit that we choose to call "Zero Volts", and use as a reference when measuring voltages elsewhere in the circuit.

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Since voltages are relative to ground, that would be positive. And ground (or power supply return) would be the negative part.

"What is ground and what does it do?"

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  • \$\begingroup\$ "And ground (or power supply return) " So if we connected a LED between the 3.3V and the Ground temrminals, is this the same as doing so with a Battery and a LED? Is this a correct visualization? \$\endgroup\$ – buntybudia Aug 13 '15 at 4:12
  • \$\begingroup\$ Yes. Although we usually don't since there's a decent chance that this will burn out the LED. \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 13 '15 at 4:13
  • \$\begingroup\$ So then also if we connected something to the 3.3V terminal but not the ground, wouldnt this cause the circuit to not be complete and fail?(Like would be the case with a simple battery-to-led-to-battery circuit? \$\endgroup\$ – buntybudia Aug 13 '15 at 4:15
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    \$\begingroup\$ The ground connection is not the only way to complete the circuit, it is simply the most convenient. If we connect to a GPIO instead then we can control whether the circuit is complete or not by changing the output. \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 13 '15 at 4:19
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    \$\begingroup\$ Actually, a correction. Since we can control the voltage from the GPIO, we can control whether or not current will flow. The circuit will always be complete regardless. \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 13 '15 at 4:26

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