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Problem reading multiple mains voltages with microcontroller.

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schmitt trigger:
I second what Richard Crowley mentions in his previous post.

A small transformer is your best friend.

Edit; In your schematic above this post, the NEUTRAL line will see 330 Vpk from the bridge rectifier’s negative terminal GND.

microherb:

--- Quote from: Richard Crowley on May 14, 2019, 09:30:35 am ---Nothing but a transformer will safely isolate you from the mains. Otherwise, you are playing with fire, quite literally.  It doesn't have to be a very big transformer.  I use the little transformers recycled out of old LINEAR wall-warts.  This is when it pays to have a well-stocked junk box.



--- End quote ---

Thanks, yes transformer is good for isolation, smallest one seems to be about 1VA, footprint is a bit large for the application, it's a production design not a one off so I would need to find something available for purchase at a reasonable price.

Marco:

--- Quote from: microherb on May 14, 2019, 10:20:47 pm ---Traditionally, there is a capacitor across the low side of the flyback transformer to the switcher ground (Bridge neg) for EMC.  I take it that is still OK with the low side of the output now tied to neutral?

--- End quote ---

Sure, the direct connection to neutral is going to win over anything the capacitor can do.

Richard Crowley:
There are opto-isolators used for voltage feedback on SMPS circuits.
With that kind of device, surely you could devise a circuit that would sample a calibrated fraction of the mains voltage.
For example: 

microherb:

--- Quote from: Richard Crowley on May 15, 2019, 01:46:51 am ---There are opto-isolators used for voltage feedback on SMPS circuits.
With that kind of device, surely you could devise a circuit that would sample a calibrated fraction of the mains voltage.
For example: 



--- End quote ---

Thanks Richard, do you have a source for the device in that document?

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