Hi, I show you a little project that I consider to Arduino can be very interesting.
It relies basically on a clock generated from Millis () function Atmega 328p pu, which also controls the lighting of a strip of 4 digit 7 segment, this strip 7 segment is recycled from an old decoder tv, has 12 pin, 8 for each common segment and four that make common for each anode. So I connect directly to the Arduino pin twelve i control it by persistence of vision i turned off the ignition sequence of each. The four control pins that control the activation of each digit, connect them to a follower of current created from LM324 opamp operational, although its output power was rather short and I had to connect a pull-up resistor 220 to each output. Finally incorporates two buttons, located at the rear, connected to the analog inputs of the Atmega, you can fix hours and minutes.
The Atmega 328 is placed on a plate with its 16Mhz oscillator, its 22pf capacitors, its reset button and terminals to connect 5v. Very basic.
The power supply, I perform with an external charger 9v, recycled, so inside the clock incorporated a 7805, a 5v voltage regulator that powers the system.
As for the box, basically the final size is about 10 * 8 * 5 cm, the front of the cover to replace it with a sheet of plywood in the middle, with a dremel type tool and cutter, make enough recess so that the displays are shown.
I put a series of photographs and videos that I think are very explanatory, but if any doubt is generated, glad to help.
I also show you a few pictures of accessory made for the mini tool to make the recess area on the plywood display.
The control program is very simple, I leave a copy if it can be an indication. I hope I have been sufficiently explanatory, although I'm available to resolve questions or issues that may arise. Thank you for your attention