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Topic: Experiments with Earthing (Read 2212 times) previous topic - next topic

dkl65

Hello!
I did an experiment with Earthing and my Arduino UNO. I connected an AC to DC 5V 1A adapter with a USB port to a surge protector (power bar). I used the USB lead to power my Arduino by plugging it into the adapter and the USB port of the UNO. I connect an the long leg of an LED to 5V, and the short leg to the Earth socket of an outlet in the power bar. The LED lit up dimmly! I used a multimeter set to 2V range, and measured a small voltage (I forgot what) between the 5V pin and the Earth socket. I connected the multimeter between the GND pin of the Arduino and Earth socket, and measured about 0.026V (I think). But it kept changing and fluctuating to -0.026V and voltages between those. Am I measuring AC? Would it be safe to measure the resistance between the GND pin and Earth socket?
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Jack Christensen

#1
May 24, 2012, 02:59 am Last Edit: May 24, 2012, 03:02 am by Jack Christensen Reason: 1
Why are you doing this, what are you trying to accomplish? Maybe you're just trying to answer a question? An experiment usually has the aim of verifying or disproving some hypothesis. What is your hypothesis?

The 5V DC supplied by the AC adapter is isolated from the mains by a transformer. This means that there is no common reference point between the two. The ground (or earth) on the power bar has nothing to do with the Arduino's ground. So in measuring between the two, just stray voltages and associated weak currents will be seen.

Assuming all is wired correctly (house wiring, breaker box, etc.), there may be little harm in such experiments so long as only the ground from the power bar is involved. Nevertheless, you are dangerously close to mains voltages, and as I can see no point in the whole experiment, I have to strongly discourage it.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

dkl65

Quote
Why are you doing this, what are you trying to accomplish? Maybe you're just trying to answer a question? An experiment usually has the aim of verifying or disproving some hypothesis. What is your hypothesis?

I did this experiment out of curiosity. I had a large discussion on Earthing before at http://arduino.cc/forum/index.php/topic,104134.0.html. My hypothesis: there is voltage between the Earth socket the Arduino 5V pin when the Arduino is connected to Earth somehow (e.g. desktop or adapter). Hypothesis: proved. The LED lit up dimmly. That means that there is a high resistance between the Earth and the Arduino (some common ground). "The question [in an experiment], if asked effectively, will generate more questions.". The new question: what am I measuring between the Earth and Arduino GND? Jack Christensen suggested "stray voltages". What are they caused by? Earthing, I may never fully understand.
Visit http://www.glenof.webs.com/!

Jack Christensen

#3
May 24, 2012, 03:53 am Last Edit: May 24, 2012, 03:57 am by Jack Christensen Reason: 1
I usually think of stray voltage as inductively or capacitively coupled voltages caused by weak but normal environmental electric and magnetic fields. Evidently the IEEE had a working group on the subject, read more here: http://en.wikipedia.org/wiki/Stray_voltage

Most stray voltages are never noticed without test equipment, but one well known exception is voltages induced in steel livestock feeding or watering troughs that were close to high-voltage power transmission lines.

I would disagree with the idea that an Arduino is "connected to earth somehow" by means of an AC adapter or PC. And before someone says that everything is connected to everything because there are no infinite resistances, from a practical standpoint there should be no significant conductivity across an AC adapter or a PC. So such an arrangement does not constitute an electrically good ground. This is the kind of thing UL, etc. insists on in consumer products. So if it's good enough for them, it's good enough for me. XD

So I'd say the experiment verified that stray voltages do in fact exist. It is an interesting topic.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

dkl65

They stray voltages I saw were between two distant grounded objects (power bar Earth socket + Arduino). The Arduino is distant, because it has a high resistance path to the Earth, as you suggested. It is all part of an interesting, but complicated subject: Earthing. If you look the linking to my other Earthing thread, I used an Arduino EMF Detector that measures EMFs around appliances. It can read voltages due to capacitive coupling between the AC appliance and the non-grounded Arduino, as Wikipedia said. When I connect the Arduino EMF Detector to the desktop, me touching the sensing wire causes the Arduino to read a voltage. Some people suggested that the Arduino is connected to Earth through the desktop, and I was acting as a capacitor to ground, or I am conducting mains EMF through my body.
Visit http://www.glenof.webs.com/!

Jack Christensen


Some people suggested that the Arduino is connected to Earth through the desktop, and I was acting as a capacitor to ground, or I am conducting mains EMF through my body.


I'd think the first would be by far the smallest effect, the second would depend where you were standing and what you had on your feet, and I think the last is probably the largest effect. If you have any kind of an audio amplifier available, could be a stereo receiver, guitar amp, etc., plug a cable into an input then touch just the center conductor on the connector at the other end and you'll hear either a 100Hz or a 120Hz buzz (depending on where in the world you are, and how well calibrated your ears are!  XD )
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

dkl65

#6
May 24, 2012, 10:30 pm Last Edit: May 24, 2012, 10:59 pm by dkl65 Reason: 1
Quote
I think the last is probably the largest effect.
Yes, but once I removed the USB and plugged a battery in, it no longer reads a voltage when I touch the receiving wire. I know that because of 10 indicator LEDs. Any suggestions as to why that happens?

Quote
plug a cable into an input then touch just the center conductor on the connector at the other end
What does that mean? Plug it into a wall outlet, set the radio to no particular channel, then touch the antenna? I want to do it as long as it causes no damage!
Visit http://www.glenof.webs.com/!

Jack Christensen


Quote
plug a cable into an input then touch just the center conductor on the connector at the other end
What does that mean? Plug it into a wall outlet, set the radio to no particular channel, then touch the antenna? I want to do it as long as it causes no damage!


No, we are not plugging anything into the wall! I'll use a stereo receiver for example. Well go ahead and plug the receiver into the wall as usual to power it. Now most will have audio line inputs, probably several different ones that can be selected via a switch or something on the front panel. May be labeled CD or AUX or whatever. Typically some audio component will be connected to these inputs with an RCA cable like this: http://www.outletpc.com/c8206.html

So get a cable like that, turn the receiver on, turn the volume all the way down so the speakers don't get damaged, pick an input and plug the cable into it, select that input via the receiver's front panel. Now, touch only the center conductor on the end of the cable that's not plugged into the receiver and slowly turn the volume up. You should hear a buzz coming from the speakers when you touch the cable.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

dkl65

#8
May 25, 2012, 03:01 am Last Edit: May 28, 2012, 03:15 am by dkl65 Reason: 1
Capacitive Sensing requires the Arduino board to be Earthed (e.g. USB to desktop), as stated on the playground page. When you touch the foil, or wave your hand near it (depends on resistor), readings will be triggered. Is it measuring capacitance between Earth and the hand, or something else?
You suggested that me conducting mains EMF is most probable when voltage was sensed as I touch the sensing wire. Why doesn't the Arduino pick that up when battery powered? Other people suggested issues with Earthing. It senses voltage when I place it near a power outlet, transformer, fluorescent tube, etc. but not my hand when battery powered.


News!
I powered my Arduino with a USB cable via a desktop. I put the black lead to my multimeter into the Earth socket of a nearby wall outlet, and red lead to the GND pin of the Arduino, and measured 54 ohms! I set it to 20V range, and connected the black lead to Earth socket, red lead to 5V pin, and got 5.05V! I measured the voltage between the Earth socket and Arduino GND, and the GND pin seems to be about 0.08V above Earth. The Arduino is definitely connected to the Earth via 54 ohms!
Visit http://www.glenof.webs.com/!

kf2qd

Non connected devices can have a potential difference between them. Set your Voltmeter to its lowest setting and hold the probes at arms legth apart and move them together and you will see a reading that changes depending on the distance apart. Do it under flourescent lights and it will be a larger voltage. Do it near motors or transformers for a test.

Any 2 devices will have some potential difference based on what electromagnetic fields they are exposed to, size and material. If they are connected by a conductor those potential differences will be minimized, depending on the strength of the fields each is exposed to and the size of the conductor. As the input and output of a transformer are isolated, the potential difference between them can be quite large. I have measured a 500 V potential difference that quickly dropped due to the load of the voltmeer. There was, for all practical purposes, no current (a megohm or more across the meter) but there was a potential difference.

There can be a potential difference between the ground at your power strip and the earth ground outside your house based on what is providing that potential, distance to the ground rod and the size of the wire.

AWOL

I misread the title of this thread as "Experiments with Earthling".

I'm a bit disappointed.  :D
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

dkl65


Set your Voltmeter to its lowest setting and hold the probes at arms legth apart and move them together and you will see a reading that changes depending on the distance apart. Do it under flourescent lights and it will be a larger voltage. Do it near motors or transformers for a test.
I did that, and got about 0.15mV, I think. I get larger voltages (>200mV) when touching the probes. I used an Arduino EMF Detector, and was able to measure EMFs as voltage near AC appliances.
Visit http://www.glenof.webs.com/!

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