build digital ac voltmeter...please help

[marvilos]

hi all,

please help me...
is there any one has digital ac voltmeter 100 VAC - 250 VAC and i can read the reading by using microcontroller...?
or maybe u know the good web site about it,please let me know.

thx's

 

[Nigel Goodwin]

Basically you use a DC A2D, and convert the AC to DC using a precision rectifier circuit - you then calibrate it for correct reading on a sinewave. If you want a true RMS reading, then you can buy specific (fairly expensive!) chips that will do that for you.

For a crude meter, which presumably is all you need? - you could use an attenuator followed by a simple bridge rectifier with a small capacitor, feeding the analogue input of a PIC (or other micro-controller).

 

[marvilos]

yes......i have build voltmeter but dc voltmeter and using ADC.
i still can't find on google how to make precision rectifier and calibrate it....
please let me know if you have links about this

thank you Nigel for reply me

 

[Aphromann]

use a potentiometer in place of your calibration resistor.

 

[Nigel Goodwin]

yes......i have build voltmeter but dc voltmeter and using ADC.
i still can't find on google how to make precision rectifier and calibrate it....
please let me know if you have links about this

A simple google finds this as the first hit **broken link removed**.

To calibrate it, simply adjust the input attenuator to make it read correctly, you will need another accurate meter to calibrate it against, or a known accurate voltage.

 

[bbarney]

have a look at this
**broken link removed**