The 3.5 inch board
The only board with more pixels: 320 × 480 on a 54.6 × 95.6 mm board, ST7796 in the library's table. Twice the bytes of the 2.8 inch, so its full redraw is the longest of the six, at least 61 ms on the wire at the library's 40 MHz.
What it is for
320 × 480 pixels is 153,600 of them: 307,200 bytes a frame, which at the library's 40 MHz clock is at least 61.4 ms on the wire, before the controller's own write time or anything your sketch does. Controller in the library's table: ST7796. The lit area is 48.96 × 73.44 mm, 0.153 mm a pixel, the same pixel as the 2.4 inch.
It is the main-screen size: twice the pixels of the 2.8 inch, with a menu, a chart and a status line on it at once. It is also twice the redraw.
Outline and holes
The board is 54.6 mm across and 95.6 mm tall, 1.6 mm thick, with four 4.8 mm holes 48.0 mm apart across and 88.0 mm down, 3.3 mm in from the sides. The header holes are 2.54 mm apart, 17.78 mm across, pin 1 (GND) at the left, and the header's reference is H3.
The glass module is 53.16 × 81.74 mm on the back, almost the board's width; the tail comes through a slot 8.5 mm wide and 6 mm tall. The 5 V warning box is on the left of this board, down its long edge.
The socket the panel plugs into
The ribbon goes into FPC2, a 12-way, 0.5 mm socket (KH-CL0.5-H2.0-12PIN-SMT). Its pin 1 is at the left end with the header at the top, numbered 1 to 12 left to right. What the board wires to each pin:
| Pin | Wired to | |
|---|---|---|
| 1 | GND | |
| 2 | the lamp's low side | through R1 and Q1 |
| 3, 4 | 3V3 | |
| 5, 6 | not connected | |
| 7 | DC | |
| 8 | CS | |
| 9 | SCL | |
| 10 | MOSI | |
| 11 | RST | |
| 12 | GND |
That is what the board does with each contact. The panel's own sheet does not match this socket's contacts, so this page does not print its table or rely on it; match the tail to the socket by looking at them. Nothing is read back from the glass: there is no MISO pad.
The backlight
Q1, a BSS138 N-channel transistor, sits on the low side of the lamp: its gate is the BL pad with R2 (10 kΩ) from gate to GND, its drain goes through R1 (2.2 Ω) to socket pin 2, and the lamp's high side is on 3V3. BL HIGH is lit; a BL pad nothing drives is dark.
Its two jumpers
Both are open as shipped.
GND, silkscreen GND CS, just below the socket: bridged, CS is tied to GND and the display is always selected. Do not then drive the CS pad.3V3, silkscreen 3V3 BL, at the lower right: bridged, BL is tied to 3V3 and the lamp is lit whenever there is power. Leave the BL pad unconnected.
Both are covered in the two solder jumpers.
Wiring and the constant
// 3V3 -> 3V3 GND -> GND
// SCL -> GPIO 12 MOSI -> GPIO 11 (classic ESP32: 18, 23)
// DC -> GPIO 2 RST -> GPIO 42 (classic ESP32: 2, 4)
// CS -> GPIO 10 BL -> GPIO 41 (classic ESP32: 15, 32)
LB_Display display(LB_TFT_35);#include <LonelyBinaryDisplay.h>
LB_Display display(LB_TFT_35); // the only line that changes per panelfrom lb_display import LBDisplay
from lb_panels import TFT_35 # the only line that changes per panel
d = LBDisplay(TFT_35)3.3 V only. Wiring for your board has the pins for other chips.
What is different about this one
It is the only board with a different picture: 320 × 480, ST7796, where the three 240 × 320 boards use an ST7789. Everything else is the same circuit.
What that costs is time. How long a redraw takes has the arithmetic; the figure above has the short version. A sketch that cleared and redrew the screen every loop on the 2.4 inch will visibly sweep on this one, and the fix is to redraw what changed.
When it does not work
A full redraw is 307,200 bytes, at least 61 ms at 40 MHz, so at most about 16 whole screens a second before the sketch does anything else. Redraw only what moved, or draw into a framebuffer and push it once. Thirty whole redraws a second would need a clock the library does not use.
A framebuffer here is 307,200 bytes, more than internal RAM will give. It needs PSRAM, which an ESP32-S3 board has when the module includes it and the classic ESP32 board does not. The library says so on Serial and draws straight to the glass instead; hasCanvas() tells your sketch which it got.
This panel runs at 40 MHz, twice the clock of the two smaller ones, and a long ribbon or jumper wires may not carry it. setSpiHz(20000000) before begin() halves it and doubles the redraw time; on a short ribbon you should not need it.
They are, except for pin 5, which is GND on the 2.8 and not connected here. Both count from the left with the header at the top. The reference on this board is FPC2 and its header is H3, where the 2.8 has FPC1 and H2, so a designator from one page is not the other's.
Six wires, six ways to see nothing, and how to tell them apart without a meter.
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