4n35 line sensing problem

[--BawA--]

Hello everyone.
I am making a project in which i have to sense the line voltage using microcontroller and display it on the lcd.
I have rectified the ac 220 volt . I also made a resistive voltge divider network. I want to isolate microcontroller supply with grid supply.
Is it possible to use 4n35 optocoupler to sense the line voltage before feeding it into microcontroller.
Do i have to operate 4n35 in linear region?

 

[goldsmith]

Hello everyone.
I am making a project in which i have to sense the line voltage using microcontroller and display it on the lcd.
I have rectified the ac 220 volt . I also made a resistive voltge divider network. I want to isolate microcontroller supply with grid supply.
Is it possible to use 4n35 optocoupler to sense the line voltage before feeding it into microcontroller.
Do i have to operate 4n35 in linear region?

Hi --BawA--

Yes it is possible but not very precise ! if the precision is very important for you use IL300 .

Best Wishes
Goldsmith

 

[Tunelabguy]

Here is a simpler solution. Start with the power supply for your microcontroller. Make that power supply from a low-voltage AC transformer. In addition to the usual rectification, filtering, and regulation of that power, make a separate rectifier and filter, but without a regulator. Scale this DC voltage down to a level that is compatible with your microcontroller and read it as a proxy for the high-voltage level. This will depend on the exact transformer ratio in your microcontroller power supply, but once you find out what that ration is (by direct measurement of the AC voltage), that voltage will be proportional to the main AC voltage.