SP6: Silent Desk Clock
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.
The custom circuit board is the best way I could find to make the clock run nearly silently. It drives a 30-35 ohm NEMA17 stepper motor directly through binary weighted resistors. This keeps the current low enough for the motor to be powered directly through the USB cable that feeds the Arduino Nano. The available torque is significantly less than the motor is capable of, but still powerful enough to run the clock. The motor only consumes around 0.25W so it stays very cool.
A kit is available for the custom motor driver. Etsy adds really high shipping charges to international orders, so I added a description of an alternate method of building the control circuit using only resistors and a soldering iron.
Video of the Clock in Operation
Top View of the Clock
Rear View of the Clock
Assembled Motor Controller
Alternate Controller Design