Electronics notes/Electricity and humans

From Helpful
(Redirected from Double insulated)
Jump to: navigation, search
This is for beginners and very much by a beginner / hobbyist.

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.

Some basics and reference: Volts, amps, energy, power · Ground · batteries · resistors · changing voltage · transistors · fuses · diodes · varistors · capacitors · inductors · transformers · baluns · amplifier notes · frequency generation · skin effect

And some more applied stuff:

IO: Input and output pins · wired local IO · wired local-ish IO · ·  Various wireless · 802.11 (WiFi) · cell phone

Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer ·

Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions

Audio notes: See avnotes

Microcontroller and computer platforms · Arduino and AVR notes · ESP series notes · STM32 series notes · · · ·

Less sorted: Ground · device voltage and impedance, audio and otherwise · electricity and humans · power supply considerations · Common terms, useful basics, soldering · PLL · pulse modulation · signal reflection · resource metering · SDR · Project boxes · vacuum tubes · Unsorted stuff

See also Category:Electronics.


Galvanic skin response (GSR)
This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Galvanic skin response (GSR), Electrodermal activity (EDA), electrodermal response (EDR), psychogalvanic reflex (PGR), skin conductance response (SCR), sympathetic skin response (SSR), and skin conductance level (SCL).

All are fancy names for 'how much electricity do your skin conduct'.

Some just that. Some with the implied measurement of mental state.

(Because of the varied names accumulated over time, EDA is intended as a new standard name, but some fields haven't moved yet, and existing documents use old terms.)

Sweating is a response controlled by the sympathetic nervous system, to things like

basic physics - warming up due to exertion, or environmental temperature, that mean you have to thermoregulate
health - hydration level, fever, ingestion of irritants, contact with toxins, menopause, other hormonal changes, like change in medicine, hyperthyroidism, reaction to caffeine, morphine, alcohol and other drugs, insulin levels, differences in ability to thermoregulate due to health, differences in ability to thermoregulate due to humidity
mental origins - strong forms of anger, fear, anxiety, arousal

Mental state?

The idea is that if you can control for the first set, you can measure the last few, making skin conductance one measure of emotional and sympathetic responses.

Criticism includes:

  • that's a fairly large 'if'
  • hydration level affects the response regardless
  • response varies by location, being driven by somewhat different responses
  • sweat reponse has delay, seconds to longer depending on the type of response. It becomes hard to tell what it's a reponse to.

The risks of attributing too much

It's impossible to avoid mentioning the polygraph style lie detector - which measures GSR, alongside heart rate, breating rate, and blood pressure.

All with the idea that because these are all controlled by the sympathetic nervous system rather than consciously, you can't voluntarily change them, which is the entire reason they're sold as lie detectors.

They're not longer admissible in most courts because they are unreliable at best, and .

Problems include that

  • it cannot distinguish between different forms of arousal - consider
    • anger (because of strong personal ethics)
    • worry - that this will be treated as proof, thinking of social implications
    • fear - maybe implications of the process just sunk in
    • startle response
    • sexual arousal - maybe you just have a thing for authority figures
none of which have anything to do with lies, much less guilt
  • it cannot distinguish between such responses being involunary, and such responses being triggered intentionally
remember, the indicators are very basic and low resolution. All they really measure is 'body is a little different', not how or what
  • it does not consider that people can distract themselves intentionally to suppress these responses
Which can be trained.
Also means ADHD people are just less guilty, huh?
  • it does not consider that sociopaths won't have some of these responses to start with, by definition

See also:

electrocardiography (ECG)

Measuring the heart muscle (-cardio-), which at skin surface is seen on the scale of a millivolt or so, which is quite weak.

Also, there is also typically coupling of electrical fields (and easily AC line noise), so you want to be using a differential amplifier to mostly ignore that.

And probably a shielded or twisted wire to minimize induction.

This can be amplified by a high impedance differential amplifier, preferably a instrumentation amp.

You may also want a passband filter, to avoid some disturbances.


Electromyography (EMG)

Measuring skeletal muscles (-myo-), which seems to be one the scale of dozens of millivolts (verify)}

See http://en.wikipedia.org/wiki/Electromyography


Electroencephalography (EEG)

Measuring activity in the brain (-encephalo-) - which (outside) is on the scale of a few millivolts and smaller (verify)

See http://en.wikipedia.org/wiki/EEG

Common (but approximate) EEG wave categorization

delta, δ

theta, θ

alpha α

mu μ

beta, β

gamma, γ

Electrocorticography (ECoG)

Electrocorticography (ECoG), or intracranial electroencephalography (iEEG), is like EEG but sensing directly on the brain itself, rather than from outside the skull and skin.


Magnetic resonance imaging (MRI)
Magnetoencephalography (MEG)
Functional near-infrared spectroscopy (fNIRS)

Functional near-infrared spectroscopy (sometimes Optical Topography (OT)) uses near-infrared spectroscopy to estimates the concentration of hemoglobin to estimate activity, so is useful for basic functional neuroimaging.

It is noninvasive and has high temporal resolution, but low spatial resolution and only works near the surface.

Electrooculography (EOG)

Electrooculography (EOG), a.k.a. retinal Electrooculography, basically helps record eye movements.




TENS, Transcutaneous Electrical Nerve Stimulation

Aims to desensitive nerves, so is used for short-term pain relief.

Higher frequency (and less strength?) than EMS, only enough to feel.

Electric massage is closer to TENS than EMS(verify)

See also:

EMS, Electrical Muscle Stimulation

Also known as NMES (neuromuscular electrical stimulation) and electromyostimulation.

Used to help muscle training, such as that to avoid atrophy.

It uses pulses that are strong and long enough to trigger muscle contraction, and helps engage more of an muscle that you consciously engage. It's not that effective without your help, though.

See also:


Purple wand

Static electricity, ESD, and humans

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

ESD and electronics

Avoiding ESD


On (not) causing tingling

Laptop tingle / zap

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


  • continuous tingling on exposed metal (sockets, screws, metal bodies, e.g. in your hands, on your lap)
  • felt only when the adapter is connected
  • Felt more clearly when
the contact area is small
you have good contact with the device (e.g. sweaty hands/legs)
you have good contact with the floor (e.g. no shoes or socks, moist concrete)
When measured, this is AC, and up to a few dozen volts, and usually not more than a milliAmp or two

Phone zap / tingle

Mostly similar to the laptop example above.

Many of these chargers are ungrounded wallwart-style, making this a likely thing.

One difference to the laptop case is that there are a lot more cheap-and-particularly-crappy phone chargers out there (than there are low-grade laptop adapters).

Some of them just low quality output, a few actually unsafe.

See e.g. [1] [2]

It the touchscreen doesn't work as well, or at all (interferes with the way capacitive touch works) whenever it's on a charge cable, it's probably just a low-quality charger and you can fix that by buying a better one. It can be hard to tell quality from looks. Reputable brands are a decent though not sure-fire way, and there are some decent cheaper-brand ones.

Less intentional / on not killing people

Electricity through humans

Human resistance ratings
Current through humans - where does the risk start?
More context
"It isn't the volts that kill you, it's the amps"
On current capacity

Electricity and heat

Resistive heat
On circuit breakers
On extension cords
Arcs and arc faults


Safety earth


Earth wiring within a house is there for safety.

Short version: it is a return connection that is much lower impedance than you are - and passes enough current enough that a fuse or circuit breaker would soon disconnect the live wire.

One of the main uses is earthing a conductor that should never be live - but might become so when things fail. For example, the chassis of a toaster or washing machine or such.

If they eventually break so that wiring comes loose and touches the outside, and you want to design for that possibility.

With safety earth on that chassis, that's a short across your house's breaker, which will probably trip, meaning the dangerous voltage on that chassis is on there for a fraction of a second.

(Also it's across two chunky wires that won't have any issue with that current for factors longer than that)

Even if you touch it within this time, the earth wire is much lower resistance to earth and (since this is a voltage divider) you shouldn't feel much.

Without safety earth, the live wire touching the chassis mean nothing other than that it is now at mains potential.

This has few immediate implications, but you will notice this when you next touch this and you are even vaguely earthed.

The current through you is also much lower than any real use, so there is no reason for a breaker to trip.

(Which is why RCDs exist, and complement breakers)


Earth (or earth ground) refers to a physical pole hammered into the earth somewhere nearby.

Earth wiring is connected to that pole.

Typically this is also bonded to things like radiator pipes, water pipes, steel structures. So generally all these things are at most a few ohms to this earth.

Devices like think ovens, washing machine, etc. are typically designed with safety earth, and using them safely will require that connection to earth - which, due to electrical code, usually just means 'socket with earth pin'.

Some (big) devices will even test the grounding and refuse to work if not present. Yet most will assume that your electrical wiring is not violating electric code. Just at all, or because they have an earthed plug and it's technically a code violation to have an earthed socket that isn't actually earthed.

(Note that powering things on generators is a little more interesting, ground-wise)

Earth versus ground

Residual-current devices

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Known under varied terms, including:

  • Residual-current devices (RCD)
  • Ground fault circuit interrupter (GFCI)
  • Ground fault interrupter (GFI)
  • residual-current circuit breaker (RCCB)
(Note: an RCBO is a residual-current protection and an overcurrent protection in one)
  • Earth leakage circuit breaker (ELCB)
  • Appliance leakage current interrupter (ALCI)
  • Leakage Current Detection Interrupter (LCDI)
  • FI - Fehler and I indicating current (verify)
  • Differential circuit breaker

There are apparently a few different designs. The common variant measures the current difference between the current going through the live and neutral wire, because those two currents should be exactly the same. Conceptually / component-wise, you can think of it as a small sensing transformer coil around both live and neutral wire. When current in is equal to current out, that sensing transformer outputs nothing.)

And if there is a difference, we assume that the extra current path is via ground (either the socket's safety earth, or the literal ground), and for safety we assume this might be going through a human, so it trips to cut power.

Electrical code varies when it comes to RCDs. Building styles also vary, with country and with time. Sometimes you'll see a chunky RCD on each leg/phase, at the power board, only. Others add them per socket, e.g. only in the kitchen and shower. Others protect other areas, double them up to project everything but trip smaller zones, and other variations.

You can also get RCD extension cords, which can e.g. make sense when you do electronics repair work, both

because you can get one that responds faster and for lower current,
and because it avoids annoying other people in the same house, as a faster-tripping workstation RCD one should generally avoid the house RCD from tripping.

Also, more RCDs make it a little easier to diagnose who/what tripped it.

Building sites frequently put a series of larger-and-smaller RCDs on different areas because it interrupts fewer people and makes it easier to diagnose who's tripping it.

See also:

Arc fault protectors

An arc fault is an unintended discharge between conductors, from things like

loose wiring connections
overheating wiring that broke down insulation over time (note that breakers should make that impossible)
otherwise damages wire insulation

The sparks and heat generated can further damage the wire, and lead to fire.

An arc-fault circuit interrupter (AFCI) measures

fast switching (order of 100 kHz)
of non-negligible current
sustained for a few seconds.

They seem to often be digital(verify)

They seem to often also integrate ground fault sensing.

Design safety, and certification

Double insulation

Galvanic isolation, floating outputs, floating ground

Isolation transformers

Is 120V safer than 230V?