Digital Clock with an “Analog” VFD Display

I first saw this clock—or, more precisely, this display—over a year ago. It caught my interest so much that I kept checking back from time to time and watching the evolution of the clocks built around it. Eventually, the price dropped to a relatively affordable level, so I bought one myself. As always, here’s the full review.


As I mentioned above, I first saw this display probably more than a year ago, when I discovered Taobao. I’m a big fan of all sorts of things with displays like this, so I was immediately interested.
At first, the display was sold on its own for around $55–65, apparently with a control board, though I can’t say for sure.


There was also a brief instruction sheet, but later I found the datasheet and a text description:
Recommended Operating Conditions:
• Filament Voltage: 2.4 V AC
• Filament Current: 453 mA
• Grid Voltage: 30 V
• Grid Current: 8 ~ 16 mA
• Grid Cut-off Voltage: -7 V DC
• Anode Voltage: 30 V
• Anode Current: 7 ~ 14 mA
• Luminance: 700 cd/m²
• Duty Factor: 1/13
• Pulse Width: 100 μS
• Life: 30,000 hours



A little later, ready-made clock boards and kits for assembling them started appearing on Taobao, eBay, and Amazon for roughly the same price.


All these versions came without an enclosure. Then I saw the original design and even wanted to buy one, but something held me back. I know exactly what it was: the price. $50–60, and sometimes nearly $70, is a lot of money.


Last autumn, I came across the same display again on one of the popular websites for fans of VFD and IN-tube clocks. Here’s a video from there.


The same clock, but in some sort of homemade enclosure, looks a little... rough, though it is original.


There was also an offer to buy the display with a power supply and driver board that could be connected to an Arduino. But I’m not very familiar with Arduino, so I kept waiting.


Then, in March this year, I saw exactly what I wanted at a more reasonable price, and in a nice enclosure too, on Taobao. They cost $25, plus $2 for shipping within China, for a total of $27 before the agent’s fees.

I’d already added one to the cart where I was collecting items for my next shipment, but decided to see what was available on AliExpress. There were two listings: one for the same $56, and the other for a more appealing $39.44.


I had to decide where to buy it, but then I found a $6 coupon, plus a $4 seller coupon for orders over $35 (now there’s only a $3/$35 coupon). That brought the total to $29.93, which turned out to be even cheaper than buying on Taobao. I even wondered if the seller would actually ship it. But three weeks later, I picked up an envelope from the post office with a small box inside containing my clock.



The package includes only the clock itself. The listing linked above, for $56, also includes a cable, but $17 for a cable isn’t exactly budget-friendly...


There’s a protective film stuck to the front.


There’s almost nothing on the back: a connector for the power supply and the only control button.
In practice, these clocks differ from the ones shown above in two key ways. On the plus side, they have a very neat, clearly factory-made enclosure, with laser engraving and a precisely fitted light filter. On the downside, there’s no alarm, although as far as I know the earlier versions had one.


I also found a little flaw. It doesn’t affect how the clock works, but it’s annoying. There’s engraving on the back, and part of it seems to have been done twice, slightly offset. The result makes it look like the image is doubled. I’d forgive this on an inexpensive clock, but for $40 I’d expect a neater finish.


Unfortunately, the protective film is very thick, so it won’t work as a screen protector. You’ll have to remove it either way.


A few words about the controls. At first, there was no documentation for them anywhere. The most you could find was a very brief description in Chinese in the form of a photo, so I had to figure it out myself. But when I started writing the review, I noticed that the seller had posted a manual.

They’re controlled with a single button. In short, here’s how it works:
1. Hold the button for 5 seconds to enter the time-setting mode. The hour hand flashes first; a short press moves it forward by one hour. Hold the button again for more than 3 seconds to set the minutes.
2. A single short press turns the second hand’s “sliding” mode on or off. When enabled, the hand makes a very short jump forward by +2 seconds, then steps back by one second. It looks normal. You can see the effect in the video above, but it’s shorter on this clock, so I couldn’t get a decent shot of it.
3. Double-press to increase the brightness; subsequent short presses adjust it. The brightness is shown by the minute hand pointing to the hour markers. Modes 1 through 8 set the brightness manually; 9 is automatic.
4. Triple-press to decrease the brightness. It works the same way, and since the adjustment cycles around, the previous mode is quite enough.
5. Press five times to light up all the display segments. Press the button briefly to exit this mode.
6. Hold the button for more than 10 seconds to reset the settings to factory defaults.



Next, I tried taking it apart, but the most I managed was to remove the light filter—and even that was really difficult. It fits tightly, and it’s also stuck down around the perimeter with double-sided tape. I used a utility knife, prying it up a little on one side and then working my way around the perimeter.
Unfortunately, I couldn’t get any further. It looks like the circuit board is glued to the case, but worse, there’s nothing to get a grip on from above, and trying to push it out from the connector side didn’t work.
If something had broken and I had the choice of fixing it or breaking it for good, I’d certainly have tried to dig it out somehow. But I don’t really want to risk smashing the display for no reason.


There it is, in all its glory. The display takes up practically the entire front panel. There are small gaps at the top and bottom, just a few millimeters each.


Because it’s so wide and has such small segments, it uses 17 filaments! By the way, the front panel gets noticeably warm during operation.


As usual, the display looks washed out without the light filter, so VFD displays aren’t much fun to use without one. That’s partly why I didn’t buy the earlier versions—finding a decent filter takes time....


But back to the filaments and brightness. At the minimum brightness setting, the glow is barely visible.


At maximum brightness, the glow becomes noticeable. And here I’m not sure whether the filament voltage is also being adjusted, or whether this is caused by something else.


A comparison of the minimum and maximum brightness settings. The glow starts to turn noticeably red at around brightness level 4–5.


I put everything back together, and only then realized I hadn’t even checked where the light sensor was hidden. Looking straight at it, you can see the segments and filaments through the filter, but they’re faint. In my opinion, the filter is very well chosen: it doesn’t cut the brightness too much, but it prevents inactive segments from showing through noticeably.


The viewing angle is more than adequate, but that’s thanks to the way VFD displays work—their viewing angle approaches 180 degrees.


Power consumption ranges from 250 mA at minimum brightness to 410 mA at maximum, so you can power it from a computer’s USB port.
As for everyday use, I find brightness level 4 comfortable. Level 3 feels a bit too dim, and there’s no need to go higher. I turned off auto-brightness.


One of the “fancy” features is an effect where the hands move into position when the clock is switched on. But since the clock is usually on all the time, you’ll only see it if you turn it off and back on.
Almost forgot: the dot between 12 and 1 indicates the time is after noon. The clock uses a 12-hour format, not 24-hour.


They really do look great. There should have been a photo here showing them on the monitor stand, below the screen, but monitor manufacturers just love glossy surfaces, so I couldn’t get a decent shot :(


Conclusion.
In short, they’re great. But if you look a little closer, they’re just a clock: no synchronization, no day-of-the-week display, not even an alarm. Just “hands,” a “dial,” and auto-brightness. In practice, these are simply decorative clocks, since reading the time is actually harder than on a clock with a "digital" display.

But as far as looks go, I’d give them a solid 5: they’re neat, unusual, and catch the eye, unlike ordinary clocks. Build quality gets a 5-minus, with points off for the poor-quality laser engraving.

One design drawback is that the case is almost impossible to take apart. Sooner or later, though, you’ll have to open it—for example, in about 5 years, when the battery needs replacing, unless the manufacturer used a supercapacitor instead, which is very unlikely.
The timekeeping accuracy is within the 10 seconds per month specified for the SD3078, perhaps a little better, though I didn’t measure it specifically. Over a week, it gained about a couple of seconds, which is more than good enough for me.

That’s all. I hope you found it interesting.