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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →An Arduino hollow clock uses two toothed, open rings and concealed gearing to make its hands appear to float. To build one, print and align the ring-and-gear parts, couple them as specified by the design, then connect a 5V geared stepper through a ULN2003 driver to an Arduino. The clock’s rate needs calibration: its basic timing comes from the Arduino’s internal oscillator, not a real-time clock (RTC).
How the hollow clock works
The clock replaces a solid dial with two horizontal rotating rings lined with teeth. The back ring carries the minute indication and is driven near the stepper motor. Gearing reduces that motion by 60:1 for the hour indication. Magnets and concealed mechanical geometry help produce the floating-hand appearance; the display is not a transparent screen.
Parts and tools to prepare
- Controller: an Arduino Nano, Uno, or Pro Mini, selected to match the firmware and its clock and voltage settings.
- Motor and driver: a 5V 28BYJ-48 geared stepper and a ULN2003 stepper-driver board. Use another 5V stepper only with a documented design variant and matching wiring.
- Printed components: the design’s STL files for the rings, gears, hands, base, rear panel, and decorative or index parts.
- Magnets: the documented designs use either three 8 mm × 3 mm neodymium magnets or six 8 mm × 1 mm magnets. Follow the selected design’s pockets and magnet arrangement.
- Fasteners and finishing: one newer guide specifies eight 2 mm × 10 mm self-tapping screws. Have high-viscosity grease for gear interfaces, wiring, and headers available.
- Power: a USB adapter or suitable regulated supply compatible with the board and motor arrangement.
Keep the STL set, wiring diagram, and firmware constants from the same design revision where possible. Variants can differ in controller, motor pin mapping, magnet arrangement, time-setting method, and whether an RTC is added.
Print and assemble the mechanism
1. Check the print-bed fit
Download the chosen design’s STL files and slice them for your printer. A 2026 guide says most components fit a 200 × 200 mm bed, but its decorative index is about 203 × 203 mm. That part needs a larger bed or resizing; check the sliced dimensions before printing.
#1 Best Overall
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- ⏰【Practical Functions & Features】: Plug in and use after soldering. The display brightness can be adjusted automatically according to ambient light or manually to your preference. With power-off memory and an alarm clock function, you can turn the alarm on or off and choose from 4 different melodies. The clock also accurately measures temperature. Please calibrate the temperature before first use for more accurate readings.
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- ⏰【Better Soldering Experience】: The LED clock kit features a clearly labeled circuit board with well-marked connection points, making component placement and soldering more straightforward. Its simple circuit design provides a practical way to develop soldering and hands-on electronics skills. Designed for STEM students, DIY electronics enthusiasts, and learners with basic electronics knowledge and hands-on experience.
- ⏰【Detailed Installation Manual】: A paper instruction manual is included to guide you through the assembly and soldering process for each component. You can also scan the QR code to download the PDF installation guide or find the User Manual on the Amazon product page under Product Guides and Documents.
2. Print and inspect the moving parts
Print slowly enough to preserve small gear teeth, and use supports wherever the selected STL calls for them. Deburr the worm gear and small center gear. Before adding electronics, check that each ring is round, concentric, and able to turn without binding.
3. Build the ring-and-gear stack
Assemble the rings and gears in the design’s specified order. Fit the magnets into their matching pockets and use adhesive if the design calls for it. Attach the hands and index pieces only after confirming that the rings move freely. Apply high-viscosity grease at the gear interfaces as appropriate to the design.
Rank #2
- DIY Soldering Clock Kit: 4 digital green LED display that can be set for clock, time, temperature, date, and week display with 3 kinds of display modes: time-temperature; time-date-week; time-temperature-date-week
- Time Display Options: 12/24H time display mode with whole daytime prompt function, default 7:00-21:00, includes clock correction function to improve clock accuracy
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- High-Precision Components: Single chip microcomputer IAP15W413AS or STC8G1K17, Clock IC DS1302, 5ppm high-precision crystal oscillator, plus time error correction function for high-precision timekeeping
- Educational Learning Tool: Package includes paper instructions and web page with step-by-step soldering pictures and videos, low soldering difficulty using direct plug components, widely used in schools to help students learn basic mechanical and electronic skills through circuit analysis and welding training
4. Install the motor and driver
Mount the 28BYJ-48 and ULN2003 in the base or rear panel. The basic circuit connects four Arduino output pins to the driver inputs, along with 5V and ground. Use the pin mapping in the documentation for your particular variant; do not assume that another build’s firmware or wiring uses the same pins. Check that the motor shaft and power connector clear the printed frame.
5. Upload the matching firmware
Upload the stepper firmware supplied with the selected project design. In the Arduino IDE, choose the board and clock setting that match the actual controller. Project notes warn that choosing the wrong 8 MHz/16 MHz or 3.3V/5V setting can change timing by roughly a factor of two.
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Rank #3
- This DIY assemble kits is equipped with 6 digits LED module, it's fun to build and also help you learn more professional knowledge about electronics.
- It is programmed AT89C2051 MCU chip, precise time display, 24 hours format, supporting seconds correction, countdown clock, stopwatch, counter, hourly chime and alarm clock functions.
- High quality PCB, has clearly marked the electronics components, even beginners can easily solder successfully.
- Comes with English user manual and online PDF file can check the list of components, circuit diagram and English instruction in the images, which will guide you how to finish step by step, perfect for school basic electronics experiment projects.
- The kit contains a 150MM single-head power supply line, the end with the terminal can be directly plugged into the PCB power supply socket. The other end has no terminal, and can be connected to the power supply after stripping the wire.
Set the hands and calibrate timekeeping
Set the hands mechanically
Set the hands before normal operation. In one documented assembly, you lift the clock face from the base, position the hands, and reinsert the face. Check the firmware notes for whether that variant advances the hands by an initial minute on startup, and account for that tick when setting the displayed time.
Adjust the minute interval
Start with the nominal interval of 60,000 milliseconds per minute. Compare the displayed time with a reliable reference over a consistent observation period. If the clock loses time, shorten the interval; if it gains time, lengthen it. Make smaller adjustments as the rate approaches the reference, repeating the comparison rather than trying to correct the clock by eye in one large change.
Rank #4
- Multi-functional Electronic Clock: This 24-hour clock soldering kit is equipped with a 6-digit digital tube, accurately displaying hours, minutes, seconds, and date/day of the week. It features an internal alarm system and dual modes of countdown and countup, meeting diverse time planning needs
- Dual-mode Timing: This electronic clock kit supports both countdown and countup modes. You can choose from four different countdown intervals of 5 minutes, 15 minutes, 30 minutes, and 60 minutes, or record the duration of tasks (such as the time taken to complete a test). Through visual time management, it effectively enhances focus in work and study, helping to establish an efficient time perception system
- Colorful Lighting Effects: This electronic clock kit is equipped with 8 LED diodes, presenting multiple colors including green, blue, yellow, purple, and red. It also supports five levels of brightness adjustment and five levels of speed adjustment, creating amazing lighting effects
- DIY Soldering Kit: It adopts a modular circuit design, with all components requiring self-soldering and assembly. The PCB board is clearly marked with component symbols and functions, and is combined with a reinforced acrylic shell. This not only consolidates basic electronic knowledge but also enhances practical soldering skills. It is recommended for those with basic soldering experience
- Versatile Present for Multiple Scenarios: As a better timekeeping tool than a smartphone, it is suitable for students to cultivate self-discipline, helps the elderly manage their daily routines, and meets the DIY needs of electronics enthusiasts. From basic timing to soldering practice, it combines practical value with educational significance, making it an ideal creative present for all age groups
One documented Pro Mini build reached 59,853 ms per minute after repeated comparisons. Treat that as an example for that build, not a universal setting: the right value depends on the board oscillator, motor load, friction, gear backlash, and print tolerances.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Accuracy limits and possible upgrades
The basic design is simple, but its internal-oscillator timing drifts more than an RTC-based clock. Acamar MCU Projects notes that “The clock relies on the internal oscillator of the Arduino, so it is not as precise as a RTC module.” Mechanical smoothness and a calibrated interval matter, but neither removes the oscillator’s limitations.
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If closer timekeeping is important, adding a real-time-clock module or a network time source would be a separate design enhancement; the cited base circuit does not include either. An RTC or network source also requires compatible hardware and firmware changes, so do not assume it is a drop-in part of the original build.
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