These are the design files for a simple three-button alarm clock.
3d: FreeCAD files for custom-fabricated partsfirmware: code that runs on the clock Arduinopcb: KiCad files for the clock motherboardtop_plate: KiCad files for the "front panel"
Next to the time display, there are three buttons, each with an LED above it associated with one of the three possible alarms.
A short press on these buttons cycles between three alarm modes for each of the three alarms: alarm (and LED) off; single-chime mode (LED glows red); continuous chime mode (LED glows green).
Pressing the first two buttons (i.e., left and middle button) simultaneously, the time display begins flashing, signifying we're now in time setting mode. The left button increments hours, the middle button increments minutes (resetting seconds whenever it is pressed), and the right button is the "enter" button, accepting the new time value.
Pressing the middle and right buttons simultaneously, the display changes from the usual HH:MM to MM:SS for five seconds.
The clock crystal is not perfect, and can be either fast or slow. To correct for that, it is possible to either add or drop seconds periodically.
To enter the offset correction mode, press all three buttons simultaneously. The display begins flashing very quickly, signifying we're in offset correction mode. Left decrements the value, the middle button increments the value, and the right button accepts the value.
The meaning of the offset value is as follows. For positive values, the time is moved forward by a second every 433 minutes multiplied by the value. For negative values, the time is moved backwards (i.e., the clock is slowed down) by one second every 433 minutes multiplied by the absolute value of the offset correction setting.
For example, if the offset correction value is set to -5, this means that every 5 times 433 minutes (approx 72.17 hours) a second is lost.