Bulbdial Clock

This clock kit uses colored LEDs to cast shadows which make up the hands of the clock. This is the same concept as a sundial, but much more accurate and with no need for sunlight.

This item is currently out of stock.
Sorry! We don't have that many in stock!

Product Info

  • Comes as a kit that you assemble.
  • Half-circle case with clear acrylic front.
  • Super-accurate time keeping.
  • Battery backup (included).
  • Arduino compatible.

More Images

Hackaday Review

How often do you actually see a working sundial? Off the top of my head I don't think I could name a single place to find one. But in my living room you can see the concept. After visiting [Windell] and [Lenore] at Evil Mad Scientist Laboratory this summer I finally took the plunge and ordered myself a Bulbdial Clock kit. To my delight, it's not just an uber-awesome time-piece, but the best engineered electronics kit I have ever come across.

What does this electronic clock have to do with a sundial? It uses three different colors of LEDs to cast shadows of a metal stud (called a gnomon) on the clock face for hours, minutes, and seconds. Three rings hold these LEDs, and because they are stacked on top of each other (about 1cm apart) causing the shadows to be cast at different lengths. This is of course the distinguishing factor between the three "hands". As an added benefit, the use of three primary colors of light results in an additive color effect. Where two colors overlap, a third is generated meaning there are six colors seen on the clock face most of the time.

Of course a clock is only as good as its ability to keep time. That's why we only stock Bulbdial Clock kits that come with the Chronodot. We've seen this part many times on Hackaday. It is basically a breakout board for one of my favorite ICs, the DS323x TCXO RTC. Those acronyms mean that the chip has a temperature controlled crystal built into the package for an accuracy of about 1 minute per year with a backup battery (included) that will keep the chip running for about 8 years. Technology!

The brilliance of the kit

Even with the acrylic case, the unassembled parts for the kit itself take up a very small amount of space. There is the main board PCB, two ring PCBs, and a final piece of substrate that acts as the clock face. Included are several dozen LEDs, a handful of capacitors and resistors, then some standoffs and screws. Humble beginnings.

Assembly starts very simply by soldering resistors, capacitors, and the microcontroller and barrel jack. Then things start to get pretty creative. This little laser-cut plywood jig is included in the kit and makes precise bending of the LEDs very easy. Casting a shadow that looks uniform no matter which LED is the light source is tricky. To get you close, one of the ring PCBs is actually used as a clamp while soldering the LEDs in place. Once each ring is assembled, you power it up into the test mode and tweak each of the 30 LEDs for the seconds hand. Thanks to the clamping technique, a slight bend is all it takes. For me, a lot of them were already aligned perfectly.

I've never actually seen an axial zero ohm resistor before. Previously I knew of zero ohm resistors only in surface mount as a way to jump traces on a single sided board. They're used in a similar way here, but to jump buses from one PCB to the next. This could have been done simply with pieces of wire, but the choice of using resistors is a creative solution. Not only does it make kit production for EMSL easier (just cut the tape for the number you need), the resistor body itself holds the part in place between the vertically stacked circuit boards as you solder.

The genesis of my infatuation

I've been interested in the Bulbdial clock for years. [Windell] did the right thing and blogged extensively about the development process starting with its first proof of concept which was built with just a dozen LEDs for each hand and rings of plywood, laser cut to suit.

The concept was new to me and seeing a prototype that was already exquisitely executed helped to paint an inextinguishable grin on my face. About six months later the kit hit the EMSL store and notched into a retro-look that seemed perfect for the ancient-meets-blinky design.

But [Windell] wasn't done yet. He rallied with a post almost a year later spilling the beans from the prototyping process. This isn't just a look at some home-etched boards, but all of the gory details of layout, busing from one ring to the next, charlieplexing LEDs, and much more. It's still a fascinating read if you missed it the first time around.

Plenty of avenues for hacking

This one is a ton of fun just to solder together, but there's firmware hacking to be done if you so desire. The code is Arduino-based so hacking your own features is about as simple as it could be.

Personally, this makes a pleasant night-light in my living room. But it would be trivial to add code to shut off the LEDs at the times you're normally sleeping. Another idea that goes along with that is automatic brightness adjustment. Brightness can already be adjusted with the settings buttons; you could build a little light sensor to plug into the ISP header that would affect the brightness variables based on ambient light readings.

A bit more ambitious hack, but one I've toyed with from time to time, is making this clock automatically adjust for daylight-savings time. The DS323x chip supports day, month, and year settings. With a backup battery you'd only need to set these once and the 8-year battery would keep track for you. From there it's a matter of writing a function to pull the date and calculate when daylight savings time changes need to be made. This is non-trivial but everyone needs a coding challenge, right?

What kind of hacks do you have in mind for your Bulbdial kit?



  • ATmega328.
  • Chronodot v2.1 (DS3231 RTC).
  • Clock case with clear acrylic front panel.
  • Universal-input power supply with US-type plug.

Needed for assembly

  • Soldering Iron and solder.
  • Angle cutters.
  • Screwdriver.

Helpful Information

Pay Securely With...