AC main and power supply common reference

[olvine]

Hey all..

I am working on a Digital AC voltmeter.
There are two parts in circuit one with microcontroller and having a constant 5V and 0V as VDD and VSS Power supply.
The other part contains resistors and diodes which inputs AC voltage....
The Question is how can I connect the whole circuit to one reference point ?
what happens if I connect the AC main's neutral with Power supply -ve terminal ?
What should be done to achieve the common reference..?

 

[esp1]

hi olivine,
I would repeat the advice I gave you on another Forum, don't do that, its a very bad idea.

Buy a small mains step down transformer, say 6Vac and isolate the project and yourself from the local mains supply.
E

 

[olvine]

Sir I would definitely do that. Safety is the priority. My Question and my problem at the moment is something else. I am not doing this thing practically until unless its absolutely safe.

 

[esp1]

hi,
As the project is connected directly to the local mains supply without an isolating transformer the only reference is the Neutral of the mains supply.

You may find that the Neutral is NOT at Earth potential, my local Neutral varies about 20Vdc above Earth with a low level 50Hz signal riding on the 20Vdc.

If you can get a mains transformer 'Wall Wart' to give around 9Vac out this will give electrical isolation, also you can also fullwave rectify the 9Vac and regulate to say +5Vdc to power you project.
E

 

[olvine]

To Power my project I have got very good power supplies.
I am asking that if I measure the AC voltage through my AC voltmeter how can I cater the reference voltage ?

 

[esp1]

As the project is connected directly to the local mains supply without an isolating transformer the only reference is the Neutral of the mains supply.

hi,
As I said above I do not know any other way to get a reference without using Neutral.
E

 

[olvine]

okay , Thanks Alot.