The board, pin by pin

Four pins, in this order

GND and VCC are power. CLOCK and DATA are the two signal wires from the last article. The library calls them CLK and DIO, the chip's datasheet calls them CLK and DIO, and the silkscreen calls them CLOCK and DATA — same wires, three habits.

Only the order matters, and the order is the same at both ends of the board.

What is under the display

Everything. The TM1637 is a surface-mount chip sitting on the display side, in the gap under the display's body, with two 10 kΩ resistors and two capacitors beside it.

The resistors are the pull-ups that hold CLOCK and DATA high, and they go to VCC. That is the single most consequential fact on this board: the voltage you feed VCC is the voltage those two wires will sit at, and therefore the voltage your board's pins will see. 3.3 V or 5 V is about nothing else.

The capacitors are across the supply. A multiplexed display takes its current in bursts — one digit's worth, forty times a millisecond — and the capacitors are what stop those bursts from appearing as dips on everything else sharing the supply.

The holes at the other end

The four plated holes at the far end are the same four nets as the header: GND, VCC, CLOCK, DATA. Not a pass-through to a second address — there is no such thing here — just the same wires, brought out again.

They are genuinely useful for passing power and clock along a row of displays. They are also the reason people accidentally build a row of displays that all show the same number, which more than one display goes through.

The enclosure in the box wraps the board and leaves the pins out of one end; the smoked film goes between the display and the window, and the only thing it does is make unlit segments disappear into the black instead of showing as grey bars.