One of the best features of this clock (I have one and have been messing with it a while now) is the up to 100 kHz refresh rate and an analog LCD driver circuit that makes the digits not flicker even a bit, even when dimmed, with a high speed camera.
That and the fact it's the highest precision clock display I've ever owned!
It is certainly not inexpensive, but it's more of an art piece than a practical instrument, unless your eyes can see in the thousands-of-hertz range!
Note that it's LED, with each segment driven continuously with a variable voltage for brightness control. Even most LED drivers are multiplexed, with each segment flashing for a short time then going dark. This uses a separate dedicated buffer for every segment. This design is important for working well with high-speed cameras, an obvious use.
"If we had a cellular modem, we could get the time from the cell towers, which is broadcast through a protocol called NITZ. This is how phones auto-update when you enter a different timezone, but it's somewhat unreliable depending on the carrier, and overall worse than using GPS. And I really don't want my clock to have a sim card."
Just out of curiosity, what can you do with a cellular modem but no sim card? Can you get the time?
CDMA networks broadcasted the time (from GPS) in the clear as part of the base station advertisements, so you used to see CDMA used as a precision time source without any kind of subscription required. CDMA equipment required accurate time for TDM coordination. Unfortunately GSM uses a different architecture for synchronization and does not require accurate time at all, so you have to be a subscriber to request time information and even then it is not all that reliable.
How can you access this timing I run a little mobile proxy service for myself and a few others, could add some value there. Mobile networks are quite interesting.
However, it seems that extra SIBs aren't necessarily broadcast but may be available on demand... and it wasn't clear to me whether making a on-demand SIB request can be done without SIM card.
I know this wasn't meant literally, but it does make for an interesting thought experiment - under what circumstances might it be valid to dial 911 to ask for the time?
My first thought was something like a nuclear operator - "we need to shut down the core at exactly 19:00, but our clocks are down!" so they call and wait for the operator to advise when the time is reached. Obviously contrived and not realistic, but interesting to think about.
At least in many European countries, the landline phone companies offered a short number for obtaining the time from an answering robot.
Many, many years ago, I have designed a piece of equipment that was integrated in a phone exchange and it provided vocal messages to be sent to a caller, for errors like non-existent phone number, but also for replying to the dedicated number for the time service. The messages were something like "The time at the next beep will be ... hours ... minutes ... seconds".
I have not heard about a similar service for mobile phones, because here the phone gets the time automatically and it displays it.
It's not a good idea to call 911 with non-emergencies.
But until a few decades ago, the primary way most of us to set our clocks was to call a number the phone company provided, which in our case was TI4-1212. "At the tone, the time will be ..."
If a response packet contains a good timestamp, you could initiate a 911 call, get a reply packet, and cancel the call before it reaches any actual operators.
> I designed this clock years ago, with the intention to incorporate every feature request I ever received for the previous precision clock.
My first thought after reading this statement was to add one Ethernet port to run a NTP server and have PoE capability. Completely overkill for the intended purpose, but I can't help but giggle at the thought of hanging this on a wall in a datacenter and have the clock also provide time-keeping for it.
Using 0.56” segment displays would probably let you reduce the horizontal size to below what would fit in a 1U rack mount. It would look sick at the top of the rack in my living room.
NTP will typically have about 10ms error which would be visible on this display. So for more authentic giggles PTP is recommended. With compatible switches to compensate for queuing delays and cable length. And if your provider doesn't give you a good time, put your own GPS-backed network clock on the roof. For science.
No GPS in SCIFs. Agree ntp would be great. Also I’d prefer a way to manually switch between a fixed set of time zone, or even just showing UTC always as an option.
This is insanely cool. It's a beautifully written article that covers all the major design decisions and issues that affected the final outcome. I'm considering purchasing one for myself and to support the developer. It would be a very cool addition to a homelab or tech/hacker space.
I think my own minor issue is the use of a micro-USB port instead of USB-C - I wonder why, I don't see it mentioned in the article. Maybe adding a PD controller would have complicated the already complex dance of components on the board. Standard USB can supply 5V at 1A (5.0W) no problem, so maybe that was just a simpler way to go.
> I think my own minor issue is the use of a micro-USB port instead of USB-C - I wonder why, I don't see it mentioned in the article. Maybe adding a PD controller would have complicated the already complex dance of components on the board. Standard USB can supply 5V at 1A (5.0W) no problem, so maybe that was just a simpler way to go.
You don’t need a PD controller. You need two resistors of a set value to be able to have USB-C supply 5V at up to 3A. No ICs needed on the input side.
I'll concede I didn't make it all the way through. I always have respect for people who make a physical product, especially one to sell.
I'm not really tracking the MHz signals thing considering there's the 10 MHz oscillator. It would've been interesting to see an EMI/C report. Usually I can see SMPS frequencies as a spur (especially in PFM mode).
For the 32K, at least for the H7 they recommended a ring of ground around it for some shielding. Unsure if that would've helped here. There are also micros that can use their internal RC 32K on vbat. And ones that can do USB without a crystal. The best micro is the one you know, the second best is the one you have. Maybe that's in play here.
The LED driver variability was nifty. My first reaction to large IO with tight timing would be an FPGA, but I don't know if they'd like the variable bank supply. It would probably be fine bit the solution used is interesting and works.
> It would've been interesting to see an EMI/C report.
It's a two layer board with no attempts made to keep loop areas small, it's going to be bad. Most of what I read of this seems fine at a glance but that part about EMI sticks out as complete nonsense.
Edit: I have nothing against it being a two layer stackup as part of the art of it, I however don't like that they're also claiming that it's designed to have extremely low radiated emissions while doing so.
That is not correct, with a charitable reading of the text. Which is not to say it’ll have good EMI characteristics - you never really know until you get it tested.
> Artificially confining ourselves to two layers is exactly the kind of challenge I am wont to be engulfed by. The trick, if you want the board to work well, is to work on only one layer, and keep almost the entirety of the other layer as ground. It is almost always possible to do this, if you're willing to put in enough thought. I rather find that designing circuit boards is a lot like Tetris, and once I'm in the swing of it I can route things for hours on end. It can become a multi-day trance, with dreams of signal integrity and current loop area.
Though on this subject:
> In contrast, said this one PCB designer, a thin track has a higher inductance, so if you make your power supply lines thin, you'll get a free bit of extra filtering.
Inductance in your power supply lines is bad, but I don’t have time to get into it right now.
A case would probably have it back in spec, if its even out of spec on it's own. The energy is going to be so tiny in those high frequency waves because it's just signal and clock. Never mind that they are still pretty low frequency and those traces are going to be awful emitters in that range.
The highest energy part of the device is going to be the LEDs, which are switching well below the bottom of the standard EMI compliance range (10Mhz).
That reminds me of production studio master clocks such as the bronics WCD-530W or the evertz equivalent. I'm more of a fan of the analog style such as the 1275T - https://evertz.com/products/12x5T.
I ordered one of these the same day (5/31). Arrived yesterday, built this morning in about two hours, came right up and worked. Very, very cool. Great design, great instructions.
Readit News
That and the fact it's the highest precision clock display I've ever owned!
It is certainly not inexpensive, but it's more of an art piece than a practical instrument, unless your eyes can see in the thousands-of-hertz range!
Can you perhaps refresh my memory? Been trying to find the reference and it's driving me nuts this am. Thanks.
Just out of curiosity, what can you do with a cellular modem but no sim card? Can you get the time?
My first thought was something like a nuclear operator - "we need to shut down the core at exactly 19:00, but our clocks are down!" so they call and wait for the operator to advise when the time is reached. Obviously contrived and not realistic, but interesting to think about.
Many, many years ago, I have designed a piece of equipment that was integrated in a phone exchange and it provided vocal messages to be sent to a caller, for errors like non-existent phone number, but also for replying to the dedicated number for the time service. The messages were something like "The time at the next beep will be ... hours ... minutes ... seconds".
I have not heard about a similar service for mobile phones, because here the phone gets the time automatically and it displays it.
But until a few decades ago, the primary way most of us to set our clocks was to call a number the phone company provided, which in our case was TI4-1212. "At the tone, the time will be ..."
My first thought after reading this statement was to add one Ethernet port to run a NTP server and have PoE capability. Completely overkill for the intended purpose, but I can't help but giggle at the thought of hanging this on a wall in a datacenter and have the clock also provide time-keeping for it.
There's other types of environments where you isolated users like SCIFs or really anything airgapped.
Hell: that would convince me to buy one that for my house.
I think my own minor issue is the use of a micro-USB port instead of USB-C - I wonder why, I don't see it mentioned in the article. Maybe adding a PD controller would have complicated the already complex dance of components on the board. Standard USB can supply 5V at 1A (5.0W) no problem, so maybe that was just a simpler way to go.
You don’t need a PD controller. You need two resistors of a set value to be able to have USB-C supply 5V at up to 3A. No ICs needed on the input side.
However, the 0.65/0.40 pads required for USB-C are no longer an issue for any of the board houses I have used in the past couple of years.
I'm not really tracking the MHz signals thing considering there's the 10 MHz oscillator. It would've been interesting to see an EMI/C report. Usually I can see SMPS frequencies as a spur (especially in PFM mode).
For the 32K, at least for the H7 they recommended a ring of ground around it for some shielding. Unsure if that would've helped here. There are also micros that can use their internal RC 32K on vbat. And ones that can do USB without a crystal. The best micro is the one you know, the second best is the one you have. Maybe that's in play here.
The LED driver variability was nifty. My first reaction to large IO with tight timing would be an FPGA, but I don't know if they'd like the variable bank supply. It would probably be fine bit the solution used is interesting and works.
It's a two layer board with no attempts made to keep loop areas small, it's going to be bad. Most of what I read of this seems fine at a glance but that part about EMI sticks out as complete nonsense.
Edit: I have nothing against it being a two layer stackup as part of the art of it, I however don't like that they're also claiming that it's designed to have extremely low radiated emissions while doing so.
That is not correct, with a charitable reading of the text. Which is not to say it’ll have good EMI characteristics - you never really know until you get it tested.
> Artificially confining ourselves to two layers is exactly the kind of challenge I am wont to be engulfed by. The trick, if you want the board to work well, is to work on only one layer, and keep almost the entirety of the other layer as ground. It is almost always possible to do this, if you're willing to put in enough thought. I rather find that designing circuit boards is a lot like Tetris, and once I'm in the swing of it I can route things for hours on end. It can become a multi-day trance, with dreams of signal integrity and current loop area.
Though on this subject:
> In contrast, said this one PCB designer, a thin track has a higher inductance, so if you make your power supply lines thin, you'll get a free bit of extra filtering.
Inductance in your power supply lines is bad, but I don’t have time to get into it right now.
The highest energy part of the device is going to be the LEDs, which are switching well below the bottom of the standard EMI compliance range (10Mhz).