i need to measure ac voltage any idea??

[Deexith Hasan]

i need o\p 210-240 v ac if greater than or lesser than this value i have to turn off relay???

i used 220-12v transformer & rectifier & voltage divider to give 2.5 volt for 230v ac but relay should be turn on if adc value is between 2.4 to 2.6 ie(210-240) diff is +-0.5 which is difficult & inaccurate...

i need some other idea to measure ac & disp in lcd

 

[barry]

First of all, how did you subtract 2.4 from 2.6 and get +/- .5? Secondly, if 230V gives 2.5V, then 210->2.3V not 2.4. Maybe your whole problem can be traced to arithmetic.

You've got a 300mV differential, this is well within the capabilities of even a simple 8-bit ADC to resolve. If you've got enough filtering, I don't see where your problem is.

 

[BradtheRad]

You can subtract some volts by putting a zener diode inline (or led's, diodes). This gives you an expanded scale at the output.

Relays usually open a few volts below the voltage where they close.

 

[Deexith Hasan]

using transformer input is 220 o\p 12 volt rms. bridge drop is 1.4v [full wave rectifier] so o\p is 10.6 volt...
how to find the filter capacitor needed ?

10.6 volt rms after filtering i should get 10.6*sq.root (2)=14.9 volt but getting 8.98v.....in proteus. y???

 

[barry]

using transformer input is 220 o\p 12 volt rms. bridge drop is 1.4v [full wave rectifier] so o\p is 10.6 volt...
how to find the filter capacitor needed ?

Depends entirely on:
1) How much ripple you can tolerate
2) Load

If you've got no load, you can use a very small cap.

 

[Deexith Hasan]

my load is adc of pic18f4520 mcu

 

[barry]

Instead of me doing all the work for you:
http://www.skillbank.co.uk/psu/smoothing.htm
http://waynestegall.com/audio/ripple.htm

Of course, you could have done a google search, too.