Electronics notes/Electricity and humans

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This is for beginners and very much by a beginner.

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 · · · · Shorter-range wireless (IR, ISM RF) · RFID and NFC · bluetooth · 802.15 (including zigbee) · 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

Less sorted: device voltage and impedance, audio and otherwise · Common terms, useful basics, soldering · Arduino and AVR notes · ESP series notes · PLL · signal reflection · pulse modulation · electricity and humans · resource metering · Microcontroller and computer platforms · SDR · Project boxes · Unsorted stuff

See also Category:Electronics.


ECG, electrocardiography

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.


EMG, Electromyography

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

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

EEG, Electroencephalography

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 EEG wave categorization

delta, δ

theta, θ

alpha α

mu μ

beta, β

gamma, γ

Galvanic skin response

galvanic skin response is sold as approximating mental states through measuring the electrical resistance of skin.

The idea is that skin conductivity changes based on hormones the brain produces when in a state of emotional arousal.

They are the main basis of classic lie detectors (alongside things like pulse and respiration) - the ones that are no longer admissible in court.

One problem is that it cannot distinguish between different forms of arousal ie. anger, fear, startle response, and sexual arousal.

Or distinguish from someone doing this intentionally.

Or consider that people can distract themselves intentionally. Which can be trained.

Or distinguish between people getting nervous not because of guilt but thinking of social implications or even just anger because of strong personal ethics.

Or consider that sociopaths won't have these responses.

retinal electrooculography



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 unibodies, e.g. in your hands, on your lap)
  • felt only when the adapter is connected
  • Felt more clearly when
the contact are is small (similar current focused through fewer of your neurons)
you have good contact with the device (e.g. sweaty hands)
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.
also, some electrical codes that "everything delivering more than some amount of Watts of power must be grounded"
also ground may be helpful to shield the brick's EM emission, for EMI compliance
also, companies that design for many countries may comply with many at once, meaning they're sometimes redundant beyond necessity

Adapters can also choose comply with Class II, which roughly says "insulated with enough layers that you can never really touch anything". Which is not very hard to meet. In some devices it's even more convenient than Class I, in others less.

Whether adapters are Class I or Class II is not directly relevant, as that applies mainly to the black block's dealing with wall voltage, rather than its output. However...

Connecting AC ground to DC output

As components, transformers and switch-mode units typically do not tie the AC-side ground to their output-side, because device builders want this as an option.

(There are specific categories of products where it is required, but in general it's not, and there are upsides to not doing so, e.g. avoidance of ground loops)

Wallwart adapters often don't do this either. And, since most don't use grounded plugs, can't. They are implicitly floating/isolated outputs. If they meet relevant safety specs while doing so, there's no direct added point to adding safety ground (...yet this is a more complex discussion).

It turns out that laptop adapters regularly do connect the two. If it's there on the main-side in the first place, of course.

a 2-pin on the mains side means there's no earth to be connected.
a 3-pin on the mains side, it is relatively likely (but not guaranteed) that AC ground is tied to DC output ground.

Sooo... Is grounding of the laptop (via the DC ground) a good idea or not?

In both cases it's safe, because any serious product will be meeting other certification that ensures this.

Beyond that, the best choice depends on which problem you are most interested in solving.

Not grounding the laptop (2-wallplug-pin adapters, and a few 3-pin that don't) will in theory give completely floating output. In practice capacitances in and around the power supply means it's still pulled to at most roughly half-line-voltage away (often with some line-frequency waveform on top). Often specifically due to decoupling capacitors in the design (which you need). The amount will varying with capacitor size, and (if compliant to e.g. UL) will necessarily be at a current capacity that cannot be harmful, but will often be enough to feel.

upside: avoids ground loop when you connect with common-mode interconnects
downside: can have this tingle issue

Grounding the laptop (most 3-wallplug-pin) avoids the tingle effect, by being able to siphon it off. However, you can more easily create a conductive ground loop - but only when you connect to another grounded device with a cable that connects ground to another ground-referenced device (which e.g. includes a lot of cases involving audio).

upside: avoids the tingle
downside: makes it easier to get (ground loop) interference issues on baseband interconnects - like consumer audio cables between laptop and amplifier
In more pathological cases (powered, similarly-grounded devices, including some DIY) it could even mean damage

In laptops, it is additionally possible that voltage conversion within the laptop may be inadequately filtered (often due to size constraints) and also help introduce some tingle(verify), but this would only be relevant when grounded via something else.(verify)

There are sometimes specific workarounds, e.g. if you have exactly one common mode audio connector you could isolate it (to avoid a conductive ground loop).

(Side note: a third pin on the brick's laptop-side output output will rarely/never be a separate ground. That's typically communication, e.g. identifying the power capacity of the adapter, and sometimes verification to make knockoffs harder to make)






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

Human ratings

"It isn't the volts that kill you, it's the amps"

On current capacity

Is 120V safer than 230V?

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 has both residual-current and overcurrent protection)
  • Rarth leakage circuit breaker (ELCB)
  • Appliance leakage current interrupter (ALCI)
  • Leakage Current Detection Interrupter (LCDI)
  • FI - Fehler and I indicating current (verify)
  • Differential circuit breaker

These measure the current difference between the current going through the live and neutral wire.

Because in regular service, those two should be exactly the same.

And if it is not, we can assume that the extra path is via ground (either the wire or the literal earth), and might be going through a human. And cuts power.

Component-wise, you can think of it as a transformer around both live and neutral wire. When current in is equal to current out, that transformer outputs nothing.)

They are typically part of your house's installation, not your devices.

For home installations, they trip when it's on the order of ~30mA for ~20 milliseconds (varies, e.g. with type and size of installation) because most humans will survive that, and is long enough that it it's less sensitive to stray current and inductive effects.

Yes, you can get RCD outlets and RCD extension cords, which can e.g. make sense when you do electronics repair work.

And possibly on top of a house RCD, and a more sensitive one than that, both to be a little safer, and so that typically you'll only trip your workstation and not your house.

Plus it's a little easier to diagnose who/what tripped it. Building sites may well put a series of larger-and-smaller RCDs on different areas for similar reasons.

Note that they do not replace circuit breakers, in the sense that they do no react to overcurrent. In a distribution board they are often alongside the real breaker for the same leg.

Though yes, there are models that do both in one unit, see RCBO, but with the idea(verify) that replacing them separately is probably a little cheaper, this is often only done when there's space limitations.

See also:

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 low enough that a fuse or circuit breaker would soon disconnect the live wire.

The main example is earthing a conductor that should never be live - but might become so when things fail. Consider most chassis, like the outside of your toaster or washing machine. These devices should be sturdy, but could be abused enough that something comes loose and now touches that outside, and you want to design for that possibility.

With safety earth on that chassis, that's a short across your house's breaker - also quite possibly a fuse within the device, on its live wire. Both of those will disconnect live quite quickly, meaning you'll not see the dangerous voltage for very long - and even 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 no immediate implications, but you will notice this when you next touch this and are even vaguely earthed.

And, significantly, that current path through you might be high enough to make you very unhappy or dead, long before it's enough to trip the breaker for high-current reasons.

(Which is why RCDs exist, and complement breakers)


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

Typically this is also bonded to things like radiator pipes, water pipes, steel structures, so often 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

Double insulation

Galvanic isolation, floating outputs, floating ground

Isolation transformers