This is a tiny clock built around a small OLED display.

Easy build in just an hour or so!

Things you need to buy:

0.96" Inch I2c IIC Serial 128x64 Oled LCD: http://a.co/1urMxg3

Things from Adafruit: Breadboard-friendly SPDT Slide Switch - 805 Adafruit Pro Trinket LiIon/LiPoly Backpack Add-On - 2124 Adafruit Pro Trinket - 3V 12MHz - 2010 CR1220 12mm Diameter - 3V Lithium Coin Cell Battery - 380 Adafruit PCF8523 Real Time Clock Assembled Breakout Board - 3295 Lithium Ion Polymer Battery - 3.7v 150mAh - 1317

Total cost like $50

You'll need to mill a small PCB - but wires could work too. It's pretty minimal.

You'll also need to print the enclosure if you want. I chose not to do a face plate but it might look good with one, depends what you like.

I would have gotten the Adafruit OLED but they didn't have them for sale at the time so I went with Amazon. As far as I know the Adafruit one is not going to be compatible with this but I haven't checked.

The code is pretty basic.

The battery lasts 7+ hours and probably could be increased a lot with some tricks to save power.