[PIC] How to measure unknown voltage using MCU's ADC??

[Deexith Hasan]

I want to make a voltage stabilizer using pic18f to detect the incoming AC voltage i used AC-DC 220-12v transformer and a rectifier and capacitor filter circuit...The input voltage may be anything from 175v to 275v AC.....how to measure it with MCU's ADC ?

 

[milan.rajik]

The transformer gives proportional voltage at secondary with respect to primary. You again convert it to DC using bridge rectifier. If secondary voltage is 12 V then 1.4V drop across bridge and you get 10.6V DC. You use a voltage divider and divide the voltage into two parts like 6.6 and 4V. The 4V is fed to ADC. If AC mains is 220V and secondary voltage is 12V then ADC input will be 4V. If mains voltage vary between 180V and 300V then ADC input also varies. So, for 4V value is 220V. Using this you can easily calculate the other values.

 

[D.A.(Tony)Stewart]

Normally DMM's use Vpk and convert to RMS assuming sine wave if valid.