|Number of pixels||58|
|Grayscales / Colors||2|
|Contact person||Arne Rossius|
The SimpleClock is a 4-digit digital clock using an absolute minimum of components. The display consists of 58 red LEDs (2 per segment), connected to an 8-pin ATtiny13 microcontroller. The mains frequency is used as a time base, hence an AC-AC adapter (transformer) is required to power the clock. If a DC source is used, the time will stand still and the colon won't flash.
The LEDs are driven using a technique called "CharliePlexing Plus", explained in Tim's Blog. For the LEDs connected between an I/O pin and GND or Vcc, two LEDs must be connected in series for this technique to work. For the LEDs between I/Os, two LEDs are connected in parallel (and another two anti-parallel) to get 2 LEDs for every segment. The internal resistance of the microcontroller's output pins is used for current limiting.