Display

The inner LED ring shows the hour: yellow on the hour and green on the half hour. At 12:00, the indicator is blue.

The outer LED ring shows the minutes in red. Every fifth LED is yellow, except at 12:00, where the indicator is blue. This clock does not display seconds.

Setting the Clock

Install three AAA batteries first. When you power on the clock for the first time, it starts at 12:00. Set the time by advancing the display the same way you would set a mechanical clock. There are two push buttons located between the hour LEDs near the 11 and 12 positions:

Set Slow: Advances the minutes one step at a time. The hour indicator and half-hour position advance normally as the minutes progress

Set Fast: Advances the display quickly so you can set the hour

Power

A USB-C connector is located at the 6 o’clock position for external power

Use a USB-A to USB-C cable with a 5-volt USB power adapter that has a USB-A connector

The clock will not work with a USB-C fast charger

Three AAA batteries provide backup power. Use lithium or alkaline batteries to prevent the clock from losing time when it is unplugged. 

A 32,768 Hz crystal provides timing. Two CD4060BE 14-stage counters divide the signal: one by 16,384 for a half-second signal and the other by 120 for the minute LEDs. The CD4060BE integrated circuit includes a binary counter and oscillator. It can produce selectable time delays or create signals of different frequencies. 

Two push buttons connected to the first CD4060BE chip set the clock. They are labeled Set Slow, which advances the clock slowly to set the minutes, and Set Fast, which advances it quickly to set the hours.

 The 60 outer-ring minute LEDs are arranged in six banks of ten, selected by two CD4017BE decade counters. One counter selects the correct LED position and the other selects the bank. The inner ring has 12 hour and 12 half-hour LEDs in four banks of six, also selected by two CD4017BE counters. Each CD4017BE has ten outputs, labeled 0–9, that go high one at a time with each clock input. They can also be configured to count less than 9.

 When power is first applied, a resistor-capacitor circuit with a CD4049UB inverter buffer generates a momentary reset pulse for all CD4017BE counters, setting the clock to 12:00.

The KiCad project files are available as Clockv2.zip under other files.