# From a 3.3v Pin do we separate Positive and Negative flow? If so, how?

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?

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.

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?"

• "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? – buntybudia Aug 13 '15 at 4:12
• Yes. Although we usually don't since there's a decent chance that this will burn out the LED. – Ignacio Vazquez-Abrams Aug 13 '15 at 4:13
• 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? – buntybudia Aug 13 '15 at 4:15
• 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. – Ignacio Vazquez-Abrams Aug 13 '15 at 4:19
• 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. – Ignacio Vazquez-Abrams Aug 13 '15 at 4:26