Phase to phase voltage 415V AC, 50hz to adc channel.

Thread Starter

Ravi Kumar 2

Joined Mar 8, 2016
Hello sir,
i want to read AC phase to phase voltage (i.e. between R Phase & Y phase) for microcontroller project.
How can i convert it to lower voltage by voltage divider method to low voltage, so that i can amplify with opamp.
waiting for your support.

Thread Starter

Ravi Kumar 2

Joined Mar 8, 2016
i have attached image, will it work, or any suggestion to modify it.

Mod edit: the image showed a non-isolated connection to 240VAC. Unsafe and not permitted on AAC.
Last edited by a moderator:


Joined Apr 5, 2008

You still have your circuit connected directly to the mains, wich is not allowed on this site.
Better look for an isolated sulution like the ISO122 or ISO124 isolation opamp.




Joined Jun 26, 2012
Your concept as shown is not safe and is not permitted on AAC. The reason is that a simple component failure could expose unwary users to hazardous voltages. As @GopherT suggests, a 3 phaze transformer would satisfy our requirements as well as safe and sane engineering principles. There may be other approaches (opto, IsoAmplifiers etc.) but this one won't fly and I have deleted the diagram so that we can keep the thread open and members can provide additional help.

Short answer: isolate your signals from the direct line to continue.
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Joined Jul 18, 2013
As mentioned already, but a 1PH transformer off of 415v to low voltage secondary.
No 3ph transformer required or needed.

Incidentally the citing of site violation policy seems rather arbitrary.
There have been quite a few posts today on repairing mains operated equipment with nary a mention of violation.