So basically I am learning about how data is transferred through wires for a networking course and I stumbled upon this Ben Eaters video on this topic and I got a bit confused because I know that computers use 5 volts (DC) to communicate with for example a USB device and I also know that mains power is 110 or 220 volts (AC) at 50 or 60 Hz but when Ben explains how in his oscilloscope data is been transferred by detecting transition states in fluctuations of 1 to -1 volts I interpreted this as the 1v (DC) been turned into Alternating Current in order to send data. Is Alternating Current how every data communication is carried? How is it in USB? Can someone clarify what I'm saying here, please.

Also data could be transferred reading 5 and 0 volts, or 1 and 0 volts transitions and that couldn’t be called Alternating Current right?

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    \$\begingroup\$ We don't know what Ben Eater does and why. Also you have far too many different questions. Data is transferred in any way that makes sense in that situation where it needs to be transferred. Have you tried to read how e.g. data is transferred over USB, and which USB standard you mean, as they all use different ways to transfer data, but USB does not use 5V for data. \$\endgroup\$
    – Justme
    Apr 4 '21 at 14:17
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    \$\begingroup\$ You seem to have a misunderstanding as to what DC and AC mean. Every signal has a DC component (the average value of the signal) and an AC component (the fluctuation about that average); anything with zero AC component can't exactly transmit a signal. \$\endgroup\$
    – Hearth
    Apr 4 '21 at 14:41
  • \$\begingroup\$ USB does not use 5v for signaling. The actual voltage is about 400mV. See this question if you want to know more: electronics.stackexchange.com/questions/139129/… \$\endgroup\$ Apr 4 '21 at 14:55
  • \$\begingroup\$ @user1850479 I think it differs between USB 3.x and USB 1.1/2.0; the latter I'm pretty sure use 3.3 volt signals. \$\endgroup\$
    – Hearth
    Apr 4 '21 at 15:12
  • \$\begingroup\$ Yes, the older types use higher voltage (but anyway not 5v). \$\endgroup\$ Apr 4 '21 at 15:30

The only correct answer is: It depends.

For an ethernet signal like the one Ben Eater is inspecting in that video, it fluctuates between +1 V and -1 V. For I²C, it goes between 0 V and the supply voltage for the chip, whatever that may be. For RS-232, it goes between +15 V and -15 V. For USB, it goes between 0 V and 3.3 V (yes, even though the power supply is 5 V). For SATA, it's between +0.25 V and -0.25 V.

It all just depends on the type of signalling. Everything uses different standards.

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    \$\begingroup\$ On top of it all, it also depends on what someone calls 0V. Usually this is the 'ground' or negative of a device, but when multiple devices are concerned, 0-5V for one device might be -2.5V to 2.5V of the other! \$\endgroup\$
    – Abel
    Apr 4 '21 at 15:19

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