Introduction: A Clock of Retrograde Minutes and Jumping Hours

About: I am interested in designing something curious but functional. Please take a look at my summary page,

A desk clock with retrograde minutes and jumping hours mechanisms.

  • Retrograde minutes : The minute hand moves reciprocally
  • Jumping hour : Numerical hour display that changes instantly


Necessary parts (other than 3D printed matters)

  • One SG90 type mini servo (I recommend genuine SG90)
  • Microcontroller (codes for Arduino and micro:bit are provided)
  • 2mm tapping screws

Step 1: Print Parts

  • Print all parts (number of printed parts = 7) with supplied posture.
  • Support structures are not needed.
  • To give different colors to the texts and indices, change the material during print.

Step 2: Assemble

Step 3: Adjustment

  • Codes for arduino (.ino files) and micro:bit (.hex files) are provided.
  • Start from the test code. Adjust the position of the minute hand by changing 7 values in the source code.
  • Copy the adjusted numbers to the clock code and flash.

Mar 16, 2022: I have added two parameters to tune the range of the minute hand.

#define RIGHT_END_PWM 560 // tune the position at 60min (right end) typically, 600
#define LEFT_END_PWM 2280 // tune the position at 0min (left end) typically, 2400
  1. Firstly, please tune the values above to adjust the right and left end of the minute hand.
  2. Then tune the individual values for 10, 20, 30, 40 and 50 minutes.

Step 4: Enjoy!

  • Adjustment of the minute hand is done electronically. Press tactile button(s) to move the hand.
  • Adjustment of the hour rotor is done mechanically. Just rotate it by your hand.