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

[Jeremy Elson]

It uses a comparator that has built-in hysteresis (the MCP6561). I haven't
noticed glitches yet, though admittedly I only have about a week of
experience with it so far. It'd be easy enough to add a LPF on the
comparator input, though.


On Fri, May 12, 2023 at 10:58 AM Andy Talbot <andy.g4jnt at gmail.com> wrote:

> 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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>