The ribbon, or the header
Every panel in the kit ends in the same fifteen-pin flat ribbon, which is what makes the six interchangeable. The header on the back is the other way in, for boards with no socket to plug that ribbon into.
One tail, six panels
Step the control through the sizes. The glass grows and shrinks; the ribbon, the socket and the eight pads behind it do not move. That is the fact the whole kit rests on: a circuit built around the 0.96 inch takes the 3.5 inch without a wire changing, because there is nothing panel-specific in the wiring to change.
It is also why this book can talk about "the display" rather than about six displays. Prototype on whatever is nearest and decide the size later.
Contacts down
The ribbon fits into the socket either way up, and only one of them works. The board tells you which — PINS FACE DOWN is printed next to the connector — and the silver contacts on the cable end should be facing the board when it goes in.
The socket is a ZIF: a dark bar at the back of it lifts, the cable slides in until it stops, the bar presses down. Neither movement takes force. If you find yourself pushing, the bar is still closed.
A ribbon in upside down is indistinguishable from no ribbon at all, and it is the first thing to check on a panel that has never shown anything.
The shortest cable that reaches
Three lengths ship in the case. Take the shortest one that gets there.
The ribbon is flat, unshielded, and carrying a clock that on most of these panels
is 40 MHz. That works, and it works less well the longer the cable is — the
symptom is a picture that arrives scrambled, or draws halfway and stops, rather
than one that fails cleanly. If a long cable does that, the two fixes are a
shorter cable or a slower clock, and the library takes the clock as one call
before begin().
If you are not using the ribbon
Snap eight pins off one of the header strips and solder them into the pad row. Straight header points out of the back; right-angle points along the board, which is what you want if the panel is going to stand upright in a case.
Eight wires then go to your board, and they are the same eight signals the ribbon carries. Which GPIO each of them wants is the next question, and the answer depends on your board and not on your panel.
When it does not work
Contacts down. The board says PINS FACE DOWN next to the socket, in silkscreen, because the cable will physically fit either way and only one of them makes contact. A ribbon in upside down behaves exactly like a ribbon that is not plugged in at all.
It is a ZIF socket: lift the dark bar at the back of it gently, slide the ribbon in until it stops, then press the bar down. It takes almost no force in either direction. If you are pushing hard, the flap is still closed.
Usually the cable. A long ribbon carrying a 40 MHz clock is an unshielded flat cable doing something it only just manages; try the shortest cable in the kit, and if that fixes it either keep the short one or call setSpiHz with a lower number before begin().
Then use the header. Snap eight pins off one of the strips in the kit, solder them into the row on the back, and wire those eight to your board with jumper leads. It is the same eight signals either way — the socket is a convenience, not a different interface.
The rule printed on the back of every board, and what ignoring it costs.
Three volts only →Edit this page — content/books/spi-tft-kit/the-ribbon-or-the-header.mdx
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SPI TFT LCD Display Kit, 6-Pack from 0.96 to 3.5 inch
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