This was an existing project i had made some time before.
An 8 X 10 LED matrix.
So it is not a complete build, just showing the add on
I have added to the 8 X 10 LED display a micro-processor, the ATMEGA328P running at 8MHz internal clock with Arduino bootloader.
Also a DS1307 Real Time Clock.
You can also see the programming header installed.
Step 1: Programming
Step 2: Pin Connections
From the 74HC595 shift register to the 328P micro-processor the pins to connect are:.
Pin 14 to 15
Pin 12 to 17
Pin 11 to 16.
From the CD4017 decade counter to the 328P micro-processor the pins to connect are:
Pin 15 to 18
Pin 14 to 19.
Pin connections for the RTC to the 328P ,icro-processor are
SDA to pin 27
SCL to pin 28
Ground and VCC +5v will need to be connected as well.
Step 3: Code
I couldn't copy and past so it is in a attached file.