Explain Like I'm Five

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Impedance, floating (self.explainlikeimfive)

submitted 3 months ago* (last edited 3 months ago) by half_built_pyramids to c/explainlikeimfive

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What's the difference between impedance and when a pin on a microchip is floating?

I get the basics of impedance. I'm capacitive impedance it's a build up of charge. Like air in a balloon. In resistive impedance it's a build up of the magnetic field, like a flywheel.

A floating pin isn't connected to anything reference voltage so it can fluctuate with surrounding interference or whatever.

Why do some ICs have tri state, low, high, and high impedance? Isn't high impedance the same thing as floating?

If it is high impedance that means it had to be connected to something, right? ~~Don't~~ Some kind of big capacitor or inductor in the chip?

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[–] HootinNHollerin 4 points 3 months ago* (last edited 3 months ago)

In resistive impedance it's a build up of the magnetic field, like a flywheel.

No that’s inductance not resistance. And for the flywheel analogy it’s inertance (inertia) as it’s kinetic energy.

Think of resistance as the portion of impedance that does not have a dependence on frequency, and dissipate energy in the form of heat. Capacitance and inductance together form the portion of impedance that is dependent on frequency. Further, capacitance is storage of potential energy and inductance is of kinetic energy. The charge is in motion in an inductor which created the magnetic field.

Capacitance also acts as a high pass filter (meaning it doesn’t react to / filters out high frequency inputs) and inductance as a low pass filter. There’s analogies to all this in mechanical and fluids as well. Capacitance’s high pass filtering can be thought of like a spring, and inductance like a mass or flywheel or volume of fluid in a pipe.

Floating implies not grounded, but not necessarily open circuit. Being open circuit could be thought of as having very high impedance (specifically resistance). A high enough voltage (force) would be required to cause a flow (current, arc) to close it. Floating implies it is closed circuit but not to a ground which is like a sink where the energy can dump into if no where else to go.

For chips (ICs) they often have high internal impedance so they don’t draw a lot of power through them but can still operate on the signal as intended.