Why & How
Why build an alarm clock? Why invest a lot of money and time in a self-built device? Where you can buy "normal" alarm clocks for just a few euros.
The short answer
First because it has features that no purchased device offers, and second because it's fun to build. See Assembly and Tests
Time and alarm time can be read effortlessly and glare-free even in the dark; without glasses, without pressing buttons, without having to leave the right or left side position.
The alarm clock can also be operated in the dark and with only one hand.
A first-time user can operate the alarm clock simply by looking at the front. No need to read the instructions.
It wakes you up with a pleasant, volume adjustable sound (MP3 song).
It also works reliably in the event of a power failure.
It is very accurate and independent of the reception of a radio signal, the mains frequency and the room temperature.
It does not occupy any space on the bedside table.
The alarm clock is mounted on the wall above the headboard of the bed.
The display and control elements face downwards and are particularly large.
Apart from the volume control, all elements are located on the front.
The lettering is large and rich in contrast (black on white).
Procedures like "Press this for 3 seconds and then 2x that ..." do not exist.
The LED displays permanently show the time (red) and the alarm time (yellow), so there is no doubt even at night whether and to what time the alarm is set.
They are individually dimmable. In addition, there is a tinted foil in front of them, so that you are not disturbed or even dazzled even in absolute darkness.
The rotary knob switches to the setting mode for clock or alarm time. The hours and minutes can then be adjusted using the plus and minus buttons.
Unintentional changes or deactivation of the alarm during sleep are excluded by using the switches as rotary switches.
The alarm is triggered by an MP3 file (stored on an SD card and exchangeable), the volume of which can be preset.
A snooze function is intentionally not included, as the alarm time can be easily and quickly set to any later time at any time.
A USB battery pack provides the power supply. Normally it is charged and simultaneously delivers the 5 volts required by the Arduino. In case of a power failure it takes over the power supply (in my tests for several days).
The real-time clock module is quartz controlled and also has a temperature sensor that corrects the gear speed depending on the room temperature. Thus a very high accuracy is achieved. Even if the 5-Volt supply by the Arduino is lost, the clock module continues to run with a 3-Volt button cell.