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

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@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 > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com >

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@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@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 >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-leave@lists.febo.com >> >

Jeremy, You'll have fun with that project. Thanks for sharing. I use a simple 5 or 12 VAC wall-wart and 10 k resistor directly to a MCU GPIO pin. The combo of PIC Schmitt trigger input & protection diodes plus picPET timestamping does the job without any other components. I capture 60 timestamps per second, and summarize or decimate on the PC doing the logging. I suspect your PCB would give better results for tau 0.01 to tau 1 but beyond that perhaps not much. Let me know if you have some sample data to confirm that hunch. Short-term and long-term ADEV of mains: http://leapsecond.com/pages/mains/mains-adev-mdev-gnuplot-g4.png A mains example from a picPET:     http://leapsecond.com/pic/pp06.htm A cross-country Western grid synchronization experiment -- similar to your:     http://www.leapsecond.com/pages/mains-cv/ Cheapest zero-crossing detector (YMMV):     http://leapsecond.com/pages/ac-detect/ A time-lapse cesium & webcam method to monitor and visualize mains wall clock time drift:     http://leapsecond.com/pages/tec/mains-clock-ani.gif /tvb On 5/12/2023 1:17 AM, Jeremy Elson via time-nuts wrote: > Greetings, > > Recently I've been interested in doing long-term measurements of the mains > power frequency (e.g., >