Circuit for AC measure?

Hello everybody. My question is about how to measure AC voltage with Arduino? I have 3 AC 230v outputs and I want a standalone arduino to measure those 3 voltages and I don't want to use transfomer for this. I was thinking of voltage dividers but probably I am gonna burn the Microcontroller this way. What are the other choices I have ?

I was thinking of voltage dividers but probably I am gonna burn the Microcontroller this way.

Yes.

I don't want to use transfomer for this

What are the other choices I have ?

Take up knitting.

Why do you not wish to use transformers ?

There is NO safe way to connect an arduino to an AC power system with the intent of accurate voltage measurement without using a means of galvanic isolation.

Opto-couplers will give you isolation but the ability to accurately monitor the AC system will be impaired

Transformers are the way to go

Even transformers have issues - mains wiring can pick up high voltage spikes when there
is nearby lightning or even fluorescent lights nearby, mains devices have to be able to
deal with a lot more than the nominal voltage.

The low-voltage side of a transformer will also see a spike in proportion so you need to
allow for a (say) 5V output transformer producing perhaps 20V spikes occasionally.
This means using a current-limiting resistor on the transformer output to protect the
delicate circuitry. Also the quality of mains power varies a lot - rural supplies are more
susceptible to lightning surges.

Perhaps if you tell us why you want to measure the voltage, we might be more helpful.

Though I suspect a transformer will still be involved - such as having a Pro Mini in an isolation box performing the measurements, sending serial information out via an optocoupler.

nixdorf: Hello everybody. My question is about how to measure AC voltage with Arduino?

What do you mean by "measure"?

Do you want to know exactly how many volts it is or do you just want to know if it's on/off?

MarkT: Also the quality of mains power varies a lot - rural supplies are more susceptible to lightning surges.

And itchy cows. Whenever they rub a loose power pole the lights flicker and flash.

[quote author=Coding Badly link=topic=241056.msg1730321#msg1730321 date=1400538283]

MarkT: Also the quality of mains power varies a lot - rural supplies are more susceptible to lightning surges.

And itchy cows. Whenever they rub a loose power pole the lights flicker and flash.

[/quote]

That reminds me of a talk a power utility troubleshoot gave to a Ham Radio Club meeting way back in the 70s that I attended. It's known that bad metal hardware on the pole insulators and attachments can create EMI noise that can effect local ham radio operators trying to work weak signal DX, and often Hams would call the utility co to complain. The problem is that it is often very intermittent, only acting up at certain temps or certain wind loads at certain directions, or at certain current loads, etc. To say nothing of which specific pole in a local area could be the offending one makes IDing pretty challenging.

The troubleshooter said the best method they came up with is using a simple portable radio tuned between stations, so just listening to inter-station static. Seems that then taking a sledge hammer to the base of a pole with a few hits will usually shake things up enough to cause the static level to peak up pretty reliably on poles with bad or loose hardware. So they would just walk the street hitting poles till they find the bad one. The main problem with that method is that he said the local people would often see them hitting the pole with the sledge and call 911 on them!

retrolefty: That reminds me of a talk...

XD

Thank you all for the replies. Sorry I couldn't answer earlier.. I am really not good at explaining but I gonna try :D

Let's say that I have 3x230v outputs and all I want Arduino to do is to "check" if there is a 230v or not 230v. If there is to light up an LED or not.

Using two microcontrollers you can measure more than on and off and use only one optocoupler.
If you insulate the live uC properly there is lower risk of electric shock when only using one optocoupler.

You can detect under and overvoltage, spikes and harmonics and report that over the serial link to next uC.

Pelle

nixdorf: Let's say that I have 3x230v outputs and all I want Arduino to do is to "check" if there is a 230v or not 230v.

In that case all you need is an opto isolator. Have a resistor, diode and capacitor in series to turn on the LED inside the opto isolator, then use the output to feed into a digital input.

If there is to light up an LED or not.

Do you want the arduino to do anything else because if not you don't need one.

Would a hall sensor mounted next to the primary/secondary windings give any usable data?

Have a look at this type of thing:

http://www.dx.com/p/itead-3-pin-ac-current-transformer-current-sensor-module-for-arduino-0-5a-314034#.U4vQrHKHbFY

http://www.dx.com/p/meeeno-mn-eb-cta12-digital-building-block-transformer-current-sensor-module-yellow-red-202274#.U4vQb3KHbFY

Theres more of these on ebay. Some need an input voltage some don’t. Have a look araound.

You will need to use some diodes and a small capacitor to rectify the output voltage and the voltage will be small (3 volts or less). you may want to adjust your Aref pin to less than the default 5 volts to get better granularity.

But this unit isolates the high voltage and is much safer than other methods.

Also: http://forum.arduino.cc/index.php/topic,202828.0.html

Google the following:
TA12-100
TA12L-100
TAK17-02
TA17L-04
TA14W-100
TA17-03
TA17-04
TA17-05

to see which one is a best fit.

Hey guys. The OP has already stated that he does not want to actually measure any voltages he just wants to know if they are present. So all the posts about actually measuring things are a bit meaningless.

@Pelleplutt - posting a schematic upside down is a new one for the obfuscation files real easy to follow.

I know, its up side down, they become so when using iPad....... Sometimes I remember to rotate my iPad..... Pelle