The enduring puzzle of static electricity | Hacker News Reader

The enduring puzzle of static electricity

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112 pointsEvgeniyZh20 comments

Good opportunity to share this life hack: I used to end up with a mess almost every time I used my coffee grinder, much like the picture in the article. Eventually I learned that this only happens with very dry beans. Adding a few tiny drops of water before grinding is enough to get rid of it pretty much completely. Since making coffee already involves water it’s as easy as dipping a finger and then running it through the beans.

Thanks for this tip!

I just tried, worked like a charm :)

It actually helps the extraction from the coffee grounds too, not just for reducing mess.

https://youtu.be/nLnB99VJ0HE

https://www.sciencedirect.com/science/article/pii/S259023852...

Similarly dry air can be a literal component killer when working with electronics. Sometimes a humidifier is needed to ensure static build-up doesn't go too far.

This is actually an interesting challenge for places that work with electronics assembly at an industrial scale; they have competing drives to keep humidity high for ESD mitigation, but also deal with a lot of moisture-sensitive components whose acceptable exposure to free air (after baking, but before reflow) is measured in hours (and substantially worse with higher humidity).

The wikipedia page on the triboelectric effect is particularly good, and has a hilarious cat picture.

https://en.m.wikipedia.org/wiki/Triboelectric_effect

It looks like someone got carried away with the motion-capture markers. ;)

A while back, I watched a YT video of someone making a large electret. Reading this makes me really want to make one for myself.

An electret is an item that presents a permanent static charge. It is like a permanent magnet. Has an enduring charge polarity.

The only use of an electret I know of is the electret microphone. And those use a very small electret.

In the video, the author made a large one. Hockey puck sized. He used some type of nylon. (I think I remember it right...)

n95 masks use electret filters, which allows them to capture particles much smaller than the 0.3 micron mesh size - such as coronavirus virions.

Interesting! I did not know that.

For the who knows how many times, this is worth a repeat - the 3M electrostatic force field

http://amasci.com/weird/unusual/e-wall.html

No mention of lightening! The idea that the triboelectric series is more guidelines than rules was interesting, but the metal-insulator distinction seems a bit off. Is there a triboelectric effect between two conductors? How? Why wouldn't the distribution of electrons even out in a pair of conductors, or do they mean non conducting metals? And I imagine someone has looked at triboelectric effects between crystals of varying materials - does anyone know?

>Based on our theory, the Seebeck coefficient is the fundamental source of the mysteriousness of triboelectricity.

https://journals.aps.org/prresearch/abstract/10.1103/PhysRev...

Put 2 conductors with different Seebecks in contact and you get a... thermocouple (at least?)

> Two experiments using the same sets of materials may yield two distinct orderings of the materials.

A quantum static effect?

More likely unrecorded environmental factors (temperature, humidity, etc.)

Remember, static RAM requires electric current, whereas dynamic RAM uses static electricity.

You might want to double check that. I would assume you are getting caught up on the gates of memory cells being capacitive and holding a charge. But both memory types use FET technology, and saying FETs use static electricity is sort of a stretch.

- There exists TTL SRAM.

- The state in a SRAM cell is maintained by mutual feedback of two cross-coupled amplifier-like circuits. The currents involved may be low in the case of CMOS, but that's immaterial to the design that it's not simply static electricity representing the 0 or 1 state. But power must continue to be supplied for the state to persist.

- The state of a DRAM call is actually charge on a capacitor. It leaks and so DRAM requires refresh.

The dynamic/static refers to the need or no need for refresh.

In a true CMOS cell (i.e. not in the so-called 4-transistor CMOS SRAM cell, which is actually an NMOS RAM cell), the transistors have leakage currents, but the existence of those leakage currents is irrelevant for how the RAM cell functions.

The storage capability of such a CMOS SRAM cell is determined by the electric charges stored in the gate capacitances of the transistors. If the transistors had no leakage currents, the state of the memory cell would be maintained indefinitely, without any current.

As it is, the leakage currents slowly discharge the gate capacitances, but then the positive feedback very slightly opens some of the transistors, enough to pass currents that compensates the effect of the leakage currents on the electric charge stored on the gate capacitances.

So the existence of currents in a true CMOS SRAM cell is a second order effect that would not be present with ideal components and it is not inherently necessary for the function of the cell, like it is for NMOS/PMOS/bipolar SRAM cells. Designing the value of the cell current in a non-CMOS cell is very important for determining the cell characteristics. For designing a CMOS cell, the leakage currents have little importance, even if they will determine the power consumption of the cell, when idle. The information storage capability of a CMOS cell is determined by the electric charge stored on the gate capacitances, which must be great enough to prevent changes in the gate voltages due to electrical noise or radiation events.

Both in DRAM cells and in true CMOS SRAM cells the information is stored as electric charge on capacitors. In a DRAM cell the charge decays continuously due to leakage currents, until it is refreshed. In a CMOS SRAM cell, the decay of the charge is prevented by the positive feedback circuit, which compensates the leakage currents, so no refresh is necessary, at the cost of a more complex memory cell.

See also, this wonderful Reactions static electricity video: https://youtu.be/-Buz6Sp2YTg

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