# How to detect the phase sequence of a 3-phase ac (R-Y-B or R-B-Y) using Atmega32?

I am using an 8-bit AVR microcontroller in my project to detect the phase sequence of a 3-phase AC supply. Which method shall I use to do the work with the least number of components required along with ATmega32? I have thought of using zero crossing detectors but that would need a step-down transformer(for reducing 230V ac). Is there any other convenient way? I have also found some other circuits and attached the images below . )

But my purpose is to detect the sequence using only atmega32(no transformer should be used

• What have you thought of so far? Have you got a hardware schematic? This sounds like homework so you need to show some effort or your question will be closed. Hit the edit link below your question. – Transistor Apr 23 at 6:44
• What other techniques have you found when searching for zero-cross detection circuits? – Transistor Apr 23 at 7:34

## 1 Answer

One solution would use three opto-isolators, one per phase. Use a "capacitive dropper" to feed the LED side of each opto-isolator - no transformer required. Make sure you protect those LEDs from reverse voltage when the phase goes negative.

• How to detect the sequence after that? – Rudrendu Mahindar Apr 23 at 13:30
• @RudrenduMahindar If each opto-isolator is fed by a half-wave rectifier, then each will switch on during the positive half-cycle, and off during the negative half-cycle. So just look at the order in which the three phases turn on. – Simon B Apr 23 at 21:59
• I understand that by looking at the order in which the three phases turn on, I can detect the phase sequence. How can I instruct the atmega32 to detect the sequence? – Rudrendu Mahindar Apr 24 at 9:45
• @RudrenduMahindar It's up to you to write the software for the atmega32. If each opto-isolator is connected to an I/O pin (configured as an input), then write a program to detect the order in which the inputs switch on. If it's 1 then 2 then 3 then 1 then 2 then 3... then the phase is rotating one way. If it's 1 then 3 then 2 then 1 then 3 then 2... then the phase is the other way. – Simon B Apr 24 at 10:28
• Ok, I shall think about a way to get the input sequence. Thank you @Simon B for your valuable guidance. – Rudrendu Mahindar Apr 24 at 10:39