The entire function of the circuit is controlled by IC1, the PIC IC, which has a program inside. When SW1 is pressed, the program produces rapidly changing numbers whcih gradually slow down to a final 2 numbers on display 1 and 2. These random numbers are generated by having a counter running very fast, at about 1MHz. Since it is impossible to predict, or accurately repeat a certain number due to the speed of the counter, it is effectively random. When SW1 is released, an 8-bit value generates two values from 1 to 6.
The circuit uses a method called "multiplexing", to drive both displays. Only one display is on at any one time, with each cathode being driven alternately by pins 1 and 2 of IC1. The current is amplified by the NPN transistors T1 and T2.
Sound is produced by pulsing the PCB-mounted buzzer, BZ1, on and off rapidly. The speed of pulsing will determine the pitch of the sound.
A view inside the case - note the 9 volt battery-
The battery was fairly flat.
Best option is to use 6 x AAA batteries in a 4-cell squarebattery holder.
The base was shaped from 3mm yellow acrylic and bent in a "U" shape using a strip heated and a wooden former to ensure an accurate size.
The red lenses over the displays were just 3mm acrylic sheet glued to the inside of the case. They hide the segments that are not lit.
You can use a different display as long as the pins line up the same, otherwise you will need to use connecting wires. The pin connections can be found on our Reference page.