[Benoit] was using an extremely old alarm clock which normally ran on mains power, and he plugged it in to his computer’s UPS to keep it operational during power outages. He noticed that when the UPS switched on that the clock would run fast, though, and apparently it was keeping time by watching the power system frequency. To solve this problem he created his own feature-dense clock which runs Linux.
This alarm clock has everything: seven-segment displays housed in clear epoxy, a touch interface, battery backup, the ability to retrieve the time from an NTP server, and a web interface to change the clock’s settings over the network. That was a large part of [Benoit]’s decision to have the clock run Linux; the network capabilities add a lot of functionality to the clock like the ability to send commands to other devices at particular times. The clock runs on an Aria G25 SOM and has a custom case that looks very professional.
We’re suckers for a high-quality clock builds here, and [Benoit]’s most recent project hits all of our buttons. Even though it doesn’t currently drive people insane or tell confusing time, the Linux and networking capabilities could certainly open up options!
Grid frequency derived clocks were the norm for a long time. If the grid is well maintained, then they will have a decent long term stability. https://en.wikipedia.org/wiki/Utility_frequency#Long-term_stability_and_clock_synchronization
A UPS usually doesn’t have this as a design goal.
Deriving the frequency data from the grid supply is not simple. One unit I helped design would jump several seconds unpredictably, always forwards. We eventually deduced that there would occasionally be a burst of interference pulses just at the zero cross-over that caused extra seconds to be added. Careful selection of schmitt trigger thresholds might help here. My preferred solution would probably involve a phase-locked loop.
You could have a one-shot fired on zero-crossing, that gates the signal for just shy of 1/60s. Might add some jitter, but won’t let it fire more than once per crossing. I think that’d be simpler.
Maybe one of the neighbors had an X10 device?
My digital clock did that a few years ago. I figured it was either the conductive RF signals from the PFC of my PC power supply or the news that the power grid is no longer corrected for 60Hz. I added a 0.01uF cap to the zero crossing detector on the clock and it cures the issue.
Very nice clean look
It looks nice, I like it.. But can you rely on it?
The “transparent” feature is not reurgitated here other than “seven-segment displays housed in clear epoxy”, but it is LEDs on segment pcbs with diffusor cast in epoxy: http://www.bfrigon.com/posts/projects/alarm-clock/display/
Professional for sure. I have never seen a wake-up clock sold that didn’t have that huge button that delays the signal for a few minutes after it goes off anyway. Set the wake up for that “delayed” time and get the extra sleep. Duh! You are not fooling anyone.
The end result is that you’re pressing the snooze anyhow regardless of when you set the alarm, unless it’s literally 5 minutes before you absolutely need to, and then you’re going to be pissed off all morning.
Waking up twice at least allows you to enjoy that brief moment when the bedsheets are still warm.
Use a gps module and a microcontroller, then you dont even have to worry about a network connection.
What time is it? Sorry, my clock is still booting…
What time is it? Sorry, still trying to find a satellite…
Doesn’t the problem of having the wrong time on power-up exist for every clock?
What time is it? Sorry, I’m waiting for the sun to reach its zenith…
“What time is it? Sorry, still trying to find a satellite…”
A GPS clock would need to “find a satellite” once a day and still be extremely accurate.
It would also need line of sight. “What time is it? Sorry, guess I should have used NTP so I wouldn’t have to take my clock outside once a day”
“It would also need line of sight”
This is a misconception. I built a few GPS clocks and they work very well inside, 5m (15 feet) away from the closest window. Others GPS clock makers can vouch on this :)
Or DCF77.
I really like the photos. What’s the trick? Soft light? Some post processing filter?
Hope he added a RTC chip to it as software based time keeping has a massive amount of slip. And I also hope he is not abusing an NTP server by hitting it more than once a day.
The cast display block is very impressively done! Looks great – nice to see the pictures from start to finish. I like how, after the sanding, the metal meets perfectly with the epoxy. But IMHO the design is completely ruined by the plastic box underneath, which gives it a “hobby electronics” look (in the bad sense). Also, the Linux is just terrible overkill. Why not just use a DCF77 receiver (or similar, depending on where you live) ( http://en.wikipedia.org/wiki/DCF77 ) and use an MCU-based design which could fit inside the display “block”. Then you can get rid of the overkill hardware, it’s more reliable, no Ethernet required, more simple, and much more beautiful with only the top display block. You could add some capacitive buttons to set the alarm time.
Beautiful clock! I love it. Everything looks really clean and professional. I’m a bit supprised you didn’t make it a clock/wifi-radio though as you already have all the requisite parts in it and it would just be a software mod.
In the assembly he laments a lack of a vacuum bucket, but a small amount in a jar could be vacuum degassed using a brake bleeder pump; a small handheld item that will get pretty far down in pressure. In the same small jar one could use a sling to centrifuge the jar; just be careful not to let the jar filled with polyester or epoxy resin loose.
You know, I have been thinking about how to modify a bicycle pump to run a vacuum jar, but yes, a brake bleeder pump is already a thing. Thanks. And I’m not going to ask you what made you think to mention being careful with centrifuges and messy compounds.
As the Microchip TCP/IP stack includes WiFi and an NTP client, Linux might be overkill for this project. Disclaimer: Other network stacks are available.
I really like the display!