SP6: Silent Desk Clock

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This is a nearly silent motorized desk clock using an Arduino Nano and a custom drive circuit to control a stepper motor. All the gears are exposed, and the sweep second hand provides a great look. The overall size is 9.5" (24cm) high by 9.1" (23cm) wide with a 6.15" (15.6cm) dial. Accuracy can be tuned to better than one second per day.

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The original design used a custom circuit board to drive the stepper motor. This was the quietest method I could find at the time. An even quieter stepper motor solution was added in January 2023 that uses a CNC Shield V4 with a TMC2208 and a DS3231 precision real time clock.

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The new driver has the following improvements:

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1) The clock runs quieter

2) It is more accurate

3) Components are easier to find

4) Uses more common stepper motors

5) Simplified calibration routine

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Both stepper motor driver circuits are supported, although the CNC Shield V4 method should be used for new builds. Download the Assembly Notes plus the CNC Shield V4 Addendum for the complete set of instructions. 

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The CNC Shield V4 board was originally designed for a CNC engraving machine with three stepper motors. The clock only needs one stepper motor. The default A4988 stepper motor driver was replaced with a much better Trinamic TMC2208 driver to make it run quietly. A DS3231 precision real time clock was added to one of the unused stepper motor sockets. This gives the clock an accuracy of a minute or two per year as the Arduino matches the stepper motor speed with the real time clock.

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The old-style stepper motor driver circuit drives a 30-35 ohm NEMA17 stepper motor directly through binary weighted resistors. A kit is available for the custom motor driver. An alternate method of building the circuit using only resistors is shown to avoid the high international shipping and customs charges added by Etsy. I still have a lot of custom circuit boards for this driver design. They will probably be on sale at a reduced price on Etsy until they are gone. All new clock builds should use the CNC Shield V4 design.