World Time!

by chris101

Published on July 17, 2015

This project uses my DIY bit, the stepper motor module.

A stepper motor turns in discrete steps, so that it's rate of turning can be controlled very precisely. Some stepper motors turn very fast (they are found in disk-drives, 3D printers and medical imaging devices, to give a few examples), but they also can turn very slowly, which is something most other motors have a hard time doing. Because of this ability to turn slowly, steppers work well as clock motors. This project demonstrates this use with a unique clock project.

The stepper motor is geared down so that it spins a globe exactly one revolution per day, the same rate that the Earth spins. Each day takes nearly 18,000 steps, or one step every 5.05 seconds.

External factors, imprecise calculations, and other issues affect the position of the globe, so the clock resets it's position as needed. The cloudbit provides a time signal to initiate setting the clock. In order to position the clock, the absolute position of the globe must be known. This is accomplished by including a magnetic switch in the design.

The globe is housed in a wooden box. It spins sideways, so the time is read by looking down at the equator of the globe to find the longitude where it is noon. Other times are derived by subtracting the time zone from the indicated position.


How To Make It



Build a stepper motor module, and connect it to an arduino, a cloudbit, and an LED as an annunciator for when the device is doing things:



Build a Globe Roller out of Legos, and drive it with the stepper motor. Be sure to gear the motor down sufficiently, so it runs slowly and smoothly. Add a Magnetic Switch so the position of the globe can be set automatically.




Magnet in Place

Adjust the position of the switch so that the globe is automatically positioned correctly.

The Magnetic Switch detects a small magnet glued into the globe. It's located about 200 miles off the coast of Liberia, and held in place with hot-melt glue.




The fairing is made of magnetically permeable fiber-board.


The fairing in place.

Add a lid with a hole, and a fairing to protect the guts from dust, etc.




The globe in place.

Set the globe on the rollers and align it so that it rolls in the correct direction. Calculate where it is midnight, and place that longitude at the top of the world.


Write code for the Arduino that turns the globe at the proper speed, and adjusts it when signaled to. See the file worldtime.ino, listed on the right sidebar, or download the file below:


Create an IFTTT recipe to send the "set clock" signal to the cloud bit at 8PM local time. It is the ability of the cloud bit to connect with a real-time clock that keeps this device accurate, despite any external interference.

Then stick it all together:




— use your red/cyan (or green or blue) 3D "anaglyph" glasses to see this in 3D.

The author wishes to thank littleBits forum member Alex Pikkert (@alexpikkert), for his assistance <especially his mad debugging skilz as well as those 3D chops!> and for inventing the Magnetic Reed Switch bit.

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