I wanted a word clock - they’re expensive. So I built one.

Background

This is my first electrical engineering project. I designed and assembled it from scratch. There are definitely some rough edges.

How it works

Here’s the inside of the clock:

It’s… not pretty. But it works. There’s

• An MSP430 with a 32 KHz crystal for keeping time
• A bank of mosfets to allow the MSP430 to control the 12 volt LED strips
• A set of three 8-bit shift registers to control the sections of the clock
• A power supply that outputs both 5 volts and 12 volts.
  • the 12v powers the LEDs
  • the 5v is wired to the USB port of the MSP430 launchpad, which then drops it down to 3.3v
• A single button to set the time (missing a pulldown - more on that later)
• The letters are several layers of laser printer transparency film with a pattern I designed.

More pictures

Learnings

1. A button won’t work correctly if you don’t have the appropriate pullup/pulldown resistor. When the button is pressed, it acts as if it is held for a few seconds after it is released while the voltage dissipates. A pulldown would’ve fixed this.

2. A 32 KHz crystal is not going to be exactly 32,768 Hz. This crystal was actually 32,766. Measuring the deviation of the clock over a few days helped me adjust this.

Cheers.

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