Above is the circuit diagram which is a pretty standard configuration for a small PIC. There are 8 segment drives, a-g and dp, and 3 digit drives. These use transistors to switch on each digit, so displays must be common cathode types. You can also use a PIC 16F627 instead as this also has internal clock facility.
Below can be seen the interior of the version made. There are two identical PCB's with a common reset connection. The circuit should run on 4.5 to 6 volts (3 or 4 AA batteries). The version shown used a PP3 battery but a rechargeable which is actually 8.4 volts not 9. This voltage was dropped to 7.7 volts because of the in-line diode for polarity protection.
The maximum rating for the PIC chip is 6v but they seem to survive on 8.4v BUT IT IS NOT RECOMMENDED - YOU
ARE ADVISED TOUSE NO MORE THAN 6V for the supply. Try adding a voltage regulator circuit if your supply is greater than 7 volts.
Please note the version shown has had the buttons modified and are not the same as the ones in the kit. The kit version has PCB click switches for mounting directly to the PCB. Wires can be brought from the board though to add different switches if desired.