Designing an digital rms voltometer

hello there,

hope everyone is ok...

i am trying to design an multi-range digital rms voltmeter & i have been using pic micro controller so far...the ranges i desired for 0-220v,0-500v.


i'm looking for your advice to design the circuit that will convert this 0-220v in 0-5v range for adc operation.

thank you.

H.jamil

try using a transformer (say 0- 6 VAC secondary) the secondary voltage converted to DC will be analogous to the line voltage...a potential divider network with suitable resistances will bring the voltage down to 5 VDC (at maximum voltage). There may be linearity errors..but on careful selection of resistors you could get an accurate reading..

Another method (a hack) you could use involves a digital panel meter, these are available in India very cheap, I do not know if you get them in your country. The panel meter contain an ICL 7106 chip (tons of circuits are available for this IC, check google) , this chip is used to display line voltage (3.5 digits) on a seven segment display. The signal lines for the various segments can be connected to a mcu (say 16F877A). The status of the lines could be read by the mcu and the number being displayed on each segment thus determined, this will give you a direct read out of the line voltage. The operation is quite stable and there is not much error..

thanks
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