"This is my ‘Clock Watchers Clock’ or ‘The Mesmeriser’ from Sillicon Chip Magazine June 2005. The kit was purchased from Jaycar.
It uses a AVR ATMEGA8515 as the processor.which controls the multiplexed LEDs. The LEDs are divided up in to 5 groups so they are on 20% of the time. It is still extremely bright. Timing is calculated by the zero crossing of the AC plug pack which gives the AVR an accurate 100Hz signal (Australian power). When running on battery power it relies on the AVR’s quartz crystal to keep track of time. The 12v AC input power goes through a LM2575T-ADJ buck regulator which outputs just under 6v. The various diodes used to both charge the AAA batteries and allow it to fall over to battery power in a blackout reduce the voltage to just over 5v for the AVR and LEDs.
The time is easily settable via 3 buttons on the reverse side of the PCB. It also has an alarm with a buzzer, led and the ability for the alarm to trigger arbitrary circuits."