[time-nuts] Re: Small PCB for measuring zero crossings of AC power (possible group buy?)

[Andy Talbot]

Is there any hysteresis in that?   If it's a basic opamp comparator you'll
be in trouble with the slightest crud and noise on the line.

Andy
www.g4jnt.com



On Fri, 12 May 2023 at 18:53, Jeremy Elson via time-nuts <
time-nuts at lists.febo.com> wrote:

> Greetings,
>
> Recently I've been interested in doing long-term measurements of the mains
> power frequency (e.g.,
> https://febo.com/pipermail/time-nuts_lists.febo.com/2022-March/105278.html
> ).
> I've built a small PCB that makes this easier: plug in an AC transformer
> (wall wart) that produces between 5 and 12 VAC, and my board converts it to
> a square wave that's 3.3 volts when the AC is above zero and 0 volts when
> it's below zero. This makes it compatible with even simple timestampers,
> including a low cost microcontroller-based timestampers. The input is a
> 5.5mm barrel connector, common on wall warts, and the output is an SMA
> connector.
>
> Here's a scope trace of it in operation:
> https://uploads.lectrobox.com/power-freq-board/trace1.png
>
> The yellow trace is the input at the barrel connector (the output of the
> 12VAC wall wart) and the blue is the output at the SMA connector. Here's a
> zoomed-in version showing the transition from low to high:
> https://uploads.lectrobox.com/power-freq-board/trace2.png
>
> A couple of photos of the board, and the schematic:
>
> https://uploads.lectrobox.com/power-freq-board/RevB-Top.jpg
> https://uploads.lectrobox.com/power-freq-board/RevB-Side.jpg
> https://uploads.lectrobox.com/power-freq-board/RevB-Schematic.pdf
>
> I've made a couple of these by hand for my own use but I thought other
> time-nuts might want one. If there's enough interest I could have a batch
> made by a PCB house and sell them for $25. Let me know if you'd like to buy
> one. If there's enough interest, I'll have a batch fabricated later this
> month.
>
> -Jeremy
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