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Custom Word Clock

Showing Time Through Words

The word clock PCB was designed in Eagle. This clock would have the following features:

  • Real time clock with 10 year battery back-up

  • Ambient light sensor to actively change clock brightness with environment

  • Four buttons to change the settings

  • Input power through USB C

  • RGB LEDs for full colour output

The MCU was a SAMD21, which is the same microcontroller used in the Arduino Zero.

A pogo pin programming header was designed into the board to facilitate manufacturing.

The clock was powered through a common USB 3 cable. Only the power pins were connected for this terminal

100 daisy chained Neopixels were used for the RGB LEDs. 

Four buttons were used to control the clock.

The Neopixels needed a 5V control signal, but the SAMD21 MCU only output 3.3V, so a level shifter was used.

A second USB port also existed on the board for prototyping. 

Here is the real time clock circuit, the actual clock part of this project. The battery backup allowed this system to hold the correct time for up to 10 years without external power.

An ambient light sensor was incorporated into the clock. This allowed the brightness to be automatically adapted to the surroundings. 

A sensor was chosen that was tuned to the human sensory range.

The last piece of the circuit was the 3.3V regulator. 

The MCU needed 3.3V, the Neopixels used 5V and the USB input 5V.