[time-nuts] Re: My AC measurement project & question

[Andy Talbot]

But do you want to measure anything other than mains frequency?   IF not,
waveform distortion in immaterial.
Or am I missing something here?

My mains monitor uses an old wall wart with 9V rectified but unregulated DC
out - 5V regulator on the display board.  I added an extra wire to one side
of the transformer winding which goes via a DC block capacitor and resistor
of a few kΩ to the Schmitt timer input of the PIC microcontroller.   At
several volts peak to peak, it's more than sufficient to take the Schmitt
well beyond its two switching thresholds.  Clamp diodes to Vdd and GND
within the PIC keep it to safe limits.


Andy
www.g4jnt.com



On Sun, 23 Jan 2022 at 10:44, Dave B via time-nuts <time-nuts at lists.febo.com>
wrote:

> On 23/01/2022 08:30, time-nuts-request at lists.febo.com wrote:
> > Stick with the transformer. The use of a capacitive divider is
> predicated on the line waveform always being a sine wave. Dream on! All it
> takes is one good spike down the line, maybe only 20-30V amplitude, and
> your capacitive divider passes it right on to that ADC that has a much
> lower (3.3V?) limit. Guess what goes poof?
> > ------------------------------------------------------------------------
>
> Transformers distort the waveform, unless specifically designed for that
> need.
>
>