As the first board is complete, now it is time to test if it works as a whole.

For start, for those who want to know, there is schematic (with all components pictured how they are placed on the board):

For test, to see all segments lit, their outputs were connected together and through 50 Ohm resistor to ground.

Testing with both inputs of 2-to-4 decoder connected to ground (black wires at the left side):

First input at ground, second floating (same effect as if it connected to high through resistor):

First input floating, second at ground:

Both inputs floating:

Test was done with 7.5V.

Part count:

Red LEDs:_____________56 pcs

Green LEDs:____________6 pcs

1 kOhm resistors:__________4 pcs

10 kOhm resistors:________14 pcs

20 kOhm resistors:________6 pcs

47 kOhm resistors:________6 pcs

BC557 transistors (pnp):____4 pcs

N2222A transistors (npn):__14 pcs

-----------------------------------------------

total:   110 parts

+ some wires

+ 7x9 cm perfboard

I think, this constitutes sucsessfull build of first board.

Now, there are other boards to build: 16-to4 multiplexor (for breaking 16 bit word to 4 nibbles in succession), 4-to-16 decoder, 16-to-7 encoder for digits and clock/2-bit counter (for driving the whole thing at fast rate, so all four digits are seen to be lit simultaneously).