How to measure AC voltages using ADC on an AVR micro?

[smitchell]

Hi,

I'm wanting to measure AC voltages using the ADC on an AVR micro.

Should I rectify the voltages, then feed the DC voltage into the ADC, or is there a better way?

The calculation time has to be pretty quick, so I'm guessing it would be unreasonable to sample the AC voltage and calculate an average or something...

Thanks a lot,

Sam

 

[FoxyRick]

adc ac voltage msp430

Hello,

Do you know the waveform? If so, you can just use an active rectifier (2 opamps and a few passives) to give an average DC value that you can scale in software. Take a look here if you haven't come across active rectifiers before:

https://focus.ti.com/docs/apps/catalog/resources/appnoteabstract.jhtml?abstractName=slod006b

If not, then the easiest way is to use an RMS-DC converter, like the Maxim MX536A ( **broken link removed** ). This is probably easiest anyway, especially if Maxim will send you a couple of free samples (depends where you live).

FoxyRick.

 

[amazonite]

AC voltage - ADC

Hi..You maybe use the TI's MSP430 Series. Because it include 12-Bits ADC, and Sample and Hold Circuit,and reference voltage. You can read the analog to digital value form the register easy.And it sample-rate is 100K.

 

[pixel]

Re: AC voltage - ADC

Is there any microcontroller with ADC that has dual power supply?

 

[smitchell]

Re: AC voltage - ADC

Thanks for the replies. I checked out the chips, and they look perfect for the job. My only concern is that the cost might start to add up once ive installed one for each voltage and current measurement in a 3 phase system. but i guess thats life...

Sam

 

[maryooo]

AC voltage - ADC

AVR ATmega8535 controller has a supply terminals used as reference to the ADC

 

[bobcat1]

Re: AC voltage - ADC

HI

First check if the signal level is compatible with your micro e.g for 5V micro signal level must be less then 5V in total (+-2.5V)

Second check the frequency of your signal you should sample the signal at twice the frequency rate (minimum)

Then you need to have enough place to put sample data (you need to sample 3 cycle to get reliable data )

After doing the list above you can do the math calculation to get voltage level & type

But if you only need to know voltage level just convert the signal to DC and measure the DC signal using the A2D

All the best

Bobi

The microcontroller specialist