AC Voltage Sampling program using PIC MCU

[Prince Vegeta]

Hi everyone.

I'm measuring 2 AC sources - 50Hz 230v RMS.

I read this subject about offsetting AC voltage to make it 0-5v DC one to get it in the ADC pin of PIC MCU for measuring it.

I have some questions after that:

1- How can I calculate RMS value of the signal?

I need code example of this question if you can. now 0v will be -380v peak AC voltage in real and 2.5v will be 0v and so on... now, do I need to worry about negative voltage (- signal in code?) or just calculate it then converting ADC value to actual voltage value?

2- I'm not good with op-amps so I did my offset circuit without them... like this:

is this applicable with 230v RMS means?

3- if there is harmonics, will it affect the readings made by THIS method?

4- I'm using PIC16F877A MCU, with 16MHz crystal (or should I use another?)... will it be enough to sample and measure 2-4 AC voltages (50Hz each) and display them at LCD with other small functions? gimme your recommendations.

5- I read a blog-post here that suggested adding a voltage follower to the voltage divider, then a filter... after them a 5.1v Zener diode THEN to ADC pin... is that applicable with this sinewave signal?


THX ALL

 

[tpetar]

Use transformer as interface between mains and voltage divider and rest of ADC circuit.


See existing thread maybe this can help you:
https://www.edaboard.com/threads/162880/

 

[Prince Vegeta]

I read that thread but it didn't answer my main question which is how to calulate RMS in code? because there is -ve cycle and so...

also, why I need a transformer if voltage divider does the job?