The following project is made by Latmos Electronics and you will need:
1 Arduino UNO shield
1 Temperature Sensor
5 MAX7219 modules
Here you can see a Real Time Clock (RTC) without any external hardware and five MAX7219 modules in order to display the current time and temperature. However, this isn't a simple clock as it can be used as a stopwatch as well. All you have to do is press one button and the stopwatch will be ready to start. When you press the same button again the stopwatch will start counting and on the third press it will pause. Then the fourth time you press the button the stopwatch will clear and the clock will be on the screen again. The other two buttons are used to regulate the value of the shown hour and minutes. On this screen you are also able to print strings with or no shift.
The pdf file contains the schematic of the circuit and the files for the software are below.
About the PCB design.
In the PCB design there are some differences that make the clock more functional. First of all, there is an extra button in order to reset atmega328p. Also, there is an external programmer in order to program the microcontroller instantly.
Check the VIDEO for confirmation.