A 12hr/24hr LED Clock with display control, uses a microcontroller PIC 16F84A or 16F628A and a few parts.
This LED clock may not be the easiest to build but surely it is the one with fewer parts that you can find, for that reason I call it “The ANP LED Clock”. (ANP stands for Almost No Parts.)
Here are the features on this ANP LED Clock:
- Can use common cathode or common anode 7-segment LED displays
- Displays time as 12 hours or 24 hours format.
- Allows to enable or disable the display for battery-operated circuits
- Can control the display brightness to reduce power consumption
- 7-segment LED displays are charlieplexed to reduce I/O ports usage
- PM LED indicator (optional)
- Only 10 parts needed: 1 PIC 16F84A,
- 22pF Capacitors, 2 n.o. switches, 1 4Mhz Xtal and 4 CA or CC 7segment LED displays
- Operates from 2.5 to 5.5 Volts, it can even work with a 3V coin battery
‘Almost No Parts’ 12/24hrs LED Clock - [Link]