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### Topic: How can I measure AC voltage in the range 0-250 VA (Read 65889 times)previous topic - next topic

#### AquaAirMan

##### Aug 13, 2010, 03:30 am
How can I use the Arduino to measure a variable AC voltage? The range would be 0-250 VAC.

#### zoomkat

#1
##### Aug 13, 2010, 03:38 am
You probably need to make a circuit to reduce the 0-250vac to 0-5vdc, and probably would be good to incorporate some type of electrical isolation depending on the useage.
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#### AquaAirMan

#2
##### Aug 13, 2010, 03:41 am
Any idea where I can find the circuit that would do the voltage reduction and ac/dc conversion?

#### prs09210

#3
##### Aug 13, 2010, 04:48 amLast Edit: Aug 13, 2010, 05:21 am by prs09210 Reason: 1
Is the 250V RMS?

Isolated transformer. Bridge rectifier. Capacitor. Voltage divider for the rest?

Here's my take:

You could use a multi-tap transformer so you can have selectable ranges for better accuracy...

#### RuggedCircuits

#4
##### Aug 13, 2010, 04:58 am
DMM with serial interface:

http://www.apogeekits.com/multimeter_dvm345di.htm

Accurate measurement, no isolation/safety problems, no hardware development.

--
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#### rumoon

#6
##### Aug 13, 2010, 07:26 pm
Should you be messing with what I'm guessing is mains AC supplies when you have such a limited understanding?

#### zoomkat

#7
##### Aug 13, 2010, 07:48 pm
Being creative, the schematic for the below multimeter might show some components to able to take an ac voltage and develop a +5v dc output. I haven't checked to see what the operating voltage is internal to the meter (0-3v, 0-5v, etc), but if one is careful and knowledgable, one probably modify the multimeter for adaption to the arduino.

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#### AquaAirMan

#8
##### Aug 13, 2010, 10:25 pm
Thanks to everyone for their input. This definitely points me in the right direction. While I have very limited experience with the Arduino I do have considerable experience with high voltage AC systems. I regularly work with marine HVAC control panels that use 115-1-60, 230-1-60, 230-3-60, 460-3-60 and 380/415-3-50 power circuits.

#### prs09210

#9
##### Aug 13, 2010, 10:59 pm
I don't see where in that hand-drawn schematic an AC voltage would be applied.. Am I missing something?

#### AquaAirMan

#10
##### Aug 13, 2010, 11:00 pm
Your probes would be at COM and V on the lower left side of the drawing

#### prs09210

#11
##### Aug 13, 2010, 11:14 pm
Ok.. I see the "AC" point next to "V". I was hoping for some insight as to how it measure AC voltage, but it doesn't look like there is any special circuitry other than a diode and some resistors. Oh well.

#### rumoon

#12
##### Aug 14, 2010, 12:57 am
Is it mains you're measuring (experience noted, by the way!), or is it general AC at various frequencies?

If it's just mains (50Hz/60Hz depending where you live I guess) then simply recitfying the output of a step-down transformer as earlier post should be fine (as long as you calibrate the variable resistor etc.).

If it's a huge frequency range you're after then converting to rms becomes more tricky.

#### mpeuser

#13
##### Aug 14, 2010, 01:24 amLast Edit: Aug 14, 2010, 01:26 am by mpeuser Reason: 1
Most likely I have not understood the problem...

The straightforward solution is to reduce the voltage to a ADC acceptable range, e.g. +/- 1 V. This can be done by a voltage devider of - say - 2.2M and 10 k and connect it to the ADC. The negative voltage will do no harm, as the current flowing will be < 100uA. You will see the half waves of a sinus  in the ADC. Use any integration algorithm that suits your need to get something you can call RMS...

#### zoomkat

#14
##### Aug 14, 2010, 02:07 am
Quote
Ok.. I see the "AC" point next to "V". I was hoping for some insight as to how it measure AC voltage, but it doesn't look like there is any special circuitry other than a diode and some resistors. Oh well.

I think an interesting point might be that it might be possible to attach an arduino ground to the 7106 chip "common" and the an arduino analog input to the pin 31 input. If the input is always in the 0-5v range to pin 31, then the multimeter possibly could be made into an easy arduino data logging interface.

http://kitsrus.com/pdf/7106.pdf