Hi.
I'm using arduino UNO. I'm working on a project where I have a 10M Ohm resistor between the analog pin of an Arduino and 3.3V. I have a wire from the analog pin connected to a potato. I also have a wire from GND that I hold in my hand. When I touch the potato, the analog level changes. Can closing such a circuit by holding the GND wire harm my body or heart?
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No.
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No. 3.3V is roughly around 2 AA batteries in series, and you definitely won't die from that.
(For more detail you could read this article, but it may not be reliable, because Wikipedia)
Electrical injury - Wikipedia.
It is best for you to follow this safety rule:
Don't be bare footed; always, use plastic sandel or shoes when working with electricity.
In my Digital Electronics Lab, I do not allow my pupil to work bare footed though they deal with 5V logic circuits using isolated power supply.
But bare footed does stop static electricity damage to devices!
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Life safety is first and then the device safety.
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If the Uno is plugged into a computer that is power from the mains, then there is always a possibility of a shock hazard.
To be safe, power the Uno from a battery or a battery powered laptop
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Arduino UNO Board is designed to be powerd from the 5V USB Port of 220V AC powered PC. It is very unlikey that that the 220V AC main from PC will be leaked down to the Arduino UNO Board. However, to be at the safe side, one may follow the safety rule of post #5.
Plastic shoes won't keep you from being electrocuted if you should touch another piece of grounded electronic equipment.
Best to follow the recommendations in post #8
Almost 100% PCs are 220V AC operated!!
If you have an electric train set, these run off 12V, and all the train tracks have these voltages on. Electric trains are considered safe and will not be able to conduct enough current into your body.
If you do want to kill yourself from an electric train set then solder a wire from each train track ti a thumb tack. Then stick one thumb tack into a vein in your left wrist, and the other one into your right wrist. Then maybe you stand a chance of doing your self a mischief.
That is rubbish, it is a combination of voltage and current not just current alone. You need the voltage to push the current through your body.
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Most regulatory agencies consider 50V or more to be dangerous and it has to insulated/isolated from the user.
...Just for example, studio condenser microphones use 48V "phantom power" and the pins on a male XLR connector are not protected and you can touch them. But you won't get hurt. You probably won't feel anything.
It's the current and what part of your body the current flows through that can kill you. But your body has resistance (widely variable) and the resistance limits the current (Ohm's Law).
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Well, yeah, of course apart from those in the US, Canada, Mexico, Japan and a couple of other places.
It's inconsequential though. A computer power supply is isolated, thus its supply rails float in relation to earth ground. That's why we can safely connect a monitor, printer, stereo and other mains-powered devices to it without all of them doing kaboom.
Whether or not a computer case (not its actual electronics) will be connected to safety GND depends on whether it's a laptop (not in that case) and whether it's plugged into an outlet with a connected/properly wired safety GND. Even if it isn't, touching the case can give a small jolt, but doesn't pose much of a danger. For the Arduino it's inconsequential since there's no galvanic connection between the Arduino and the computer housing since USB only connects power rails and data lines, no safety GND.
It's perfectly safe to touch a bare Arduino connected via a USB cable to a computer, regardless of whether the computer is a laptop or a desktop, or how it's powered.
...break it into little pieces and eat them. This will likely result in some nasty intestinal perforations that will get the job done. A horrible way to go, too...
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I remember someone told me the rule of one hand in the pocket, when they worked with very high voltage equipment in the field.
Even after all security checks, one hand in the pocket can save your life, because at least the current will not go through your heart, from one arm to the other.
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On my PC side, the shield of my USB cable is connected directly to my PC chassis and the chassis is connected to safety ground, this is probably true for most PCs
On my nano side the shield is connected directly to power ground.
So now the PC USB power ground is connected to the chassis ground through the USB cable.
I wouldn't call that galvanically isolated.
I've seen many "Arduino" designs where the USB connector shell was connected directly to ground or through some combination of resistors and or capacitors and or inductors, including official Arduinos.
The case should be isolated from power GND and ideally connected to safety GND (a.k.a. 'earth'). The two should not be electrically connected. The shield of the USB cable should be connected on either end to signal GND.
I don't think so.
Ever wondered why the standoffs that connect a computer mainboard to the case are insulated? Even in the early 1990s when we tended to use metal ones, it was good practice (although probably ignored by some amateur builders) to have insulator rings between them and the mainboard. The same with the power supply, and the PCB's in the PC's peripherals.
It's possible that in your computer, the USB shield of the cable touches a metal part of the computer case, causing a short between power GND and the case. Ideally, this doesn't happen, but poor tolerances in spacing especially around rear connectors makes this easy to occur. It's not usually a problem - after all, the power supply of the computer is isolated, so effectively floats. Grounding it through the case won't make much of a difference apart from a momentary transfer of static charge as contact is made.
To power (or more strictly signal) ground yes. Not safety ground a.k.a. 'earth'.
Fortunately, it doesn't matter in the case of OP because whether or not his (or your) computer case is erroneously connected to power GND. Touching the Arduino still isn't going to harm anyone.
Just measured on my old HP desktop - sure enough, USB shield and the case are very much NOT electrically connected. As it should be.
I have a dell and they are metal.
the USB shield of the cable touches a metal part of the computer case, causing a short between power GND and the case.
No it's purposely connected to the chassis.
To power (or more strictly signal) ground yes. Not safety ground a.k.a. 'earth'.
Of course not but that is not what i said.
Well if electocution by a faulty electrical device is never possible then I guess we all wasted our money on GFIs.
Aha.
To be clear, 3.3 or 5 volts will not damage your body.
What people are worrying about is that faulty equipment will allow higher voltages to “leak” into your low voltage supply.
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