3.5' Rotrics

ESP32 + SDReader + PSRAM + 3.5’ TFT (480x320) with Resistive touch screen
- Rotrics

Specs

ESP32
PSRAM: 8MB
FLASH: 8MB
Micro-SD card slot (SDIO 1 bit)
3.5-inch 480x320 TFT display - ILI9488 (SPI)
Capacitive touch panel - XPT2046 (SPI)
Built-in microphone
Speaker
1 USB-C (Serial 1)
1 debug port: GND, 5V, EN, GPIO 0, GPIO 2, GPIO 1 (TX), GPIO 3 (RX)
Power Supply: 5V / 1A

Important

The USB-C connector is actually a raw serial 1 port, not a real USB port.

Serial 1 is the serial port used for communication with other devices.

Serial 0 is the serial port used for programming the ESP32, this port is not easily accessible because connector is not soldered.

So do not try to flash TFT using usb-c connector, it won’t work.

Note about USB-C connector

The ESP32 serial 1 TX is on both TX3 of USB connector, and ESP32 serial 1 RX is on both RX3 of USB connector, GND is GND, 5V is 5V, D+, D-, TX6 and RX6 seems not connected.

Pins

Pin	Usage
GPIO 0	GPIO 0 / CODEC_ES8388_I2S_MCLK
GPIO 1	TX 0
GPIO 2	GPIO 2 / SDIO DAT0
GPIO 3	RX 0
GPIO 4	SDIO DAT1
GPIO 5	CODEC_ES8388_I2S_SCLK
GPIO 6	SPI FLASH
GPIO 7	SPI FLASH
GPIO 8	SPI FLASH
GPIO 9	SPI FLASH
GPIO 10	SPI FLASH
GPIO 11	SPI FLASH
GPIO 12	TFT_BL
GPIO 13	TFT_TOUCH_CS
GPIO 14	SDIO CLK
GPIO 15	SDIO CMD
GPIO 16
GPIO 17
GPIO 18	CODEC_ES8388_I2C_SDA - CE(low) wired to GND
GPIO 19	TFT_CS
GPIO 21	TX 1
GPIO 22	TFT_TOUCH_IRQ
GPIO 23	CODEC_ES8388_I2C_SCL
GPIO 25	CODEC_ES8388_I2S_LRCK
GPIO 26	CODEC_ES8388_I2S_DSDIN
GPIO 27	TFT_DC
GPIO 32	TFT_MOSI
GPIO 33	TFT_SCLK
GPIO 34	TFT_MISO
GPIO 35	CODEC_ES8388_I2S_ASDOUT
GPIO 36	RX 1
GPIO 37	SD_DETECT (Low)
GPIO 38
GPIO 39

CODEC_ES8388

Pin	Usage
ROUT1
LOUT1
ROUT2	speaker
LOUT2
RIN2
LIN2
RIN1
LIN1	microphone

3.5' ESP32-3248S035R/C

ESP32 based + SDReader + 3.5’ TFT (480x320) with Resistive or Capacitive touch screen
- Aliexpress

Features

ESP32
FLASH: 4MB* (*Up to 16MB with hardware mod)
PSRAM: NO* (*Up to 8MB with hardware mod - See Hardware Mod section below…)
Micro-SD card slot (SPI)
3.5-inch 480x320 TFT display - ST7796 (SPI)
Touch panel options:
- ESP32-3248S035R - Resistive touch panel - XPT2046 (SPI)
- ESP32-3248S035C - Capacitive touch panel - GT911 (i2C - 0x5D or 0x14)
1 RGB led
1 USB-Micro to Serial 0 (CH340C)
Boot and reset buttons
Power Supply: 5V / 1A
Header P3 : GND - GPIO 35 - GPIO 22 - GPIO 21
Header CN1 : GND - NC (or GPIO 22 on some boards) - GPIO 21 - V3.3
Header power : VIN - TX - RX - GND

Pins

ESP Pin	GPIO	Description
1	GND	Ground
2	VCC	+3V3
3	EN	RST / TFT_RST (Reset / LCD)
4	GPIO36	SENSOR_VP / RTP_IRQ (Res. Touchscreen)
5	GPIO39	SENSOR_VN
6	GPIO34	ADC
7	GPIO35	Header P3 Pin 3
8	GPIO32	CTP_SCL (Cap. Touchscreen)
9	GPIO33	CTP_SDA (Cap. Touchscreen) / RTP_CS (Res. Touchscreen)
10	GPIO25	CTP_RST (Cap. Touchscreen)
11	GPIO26	AUDIO IN-
12	GPIO27	TFT_BL (TFT)
13	GPIO14	TFT_SCK (TFT) / RTP_CLK (Res. Touchscreen)
14	GPIO12	TFT_SDO (TFT) / RTP_OUT (Res. Touchscreen)
15	GND	Ground
16	GPIO13	TFT_SDI (TFT) / RTP_DIN (Res. Touchscreen)
17	SHD/SD2	HOLD (SPI Flash / PSRAM*)
18	SWP/SD3	WP (SPI Flash / PSRAM*)
19	SCS/CMD	CS (SPI Flash)
20	SCK/CLK	SCK (SPI Flash)
21	SDO/SD0	SO (SPI Flash / PSRAM*)
22	SDI/SD1	SI (SPI Flash / PSRAM*)
23	GPIO15	TFT_CS (TFT)
24	GPIO02	TFT_RS (TFT)
25	GPIO0	BOOT_SW
26	GPIO04	LED_RGB
27	GPIO16	LED_RGB (PSRAM_CS*)
28	GPIO17	LED_RGB (PSRAM_SCK*)
29	GPIO05	TF_CS (SD Card)
30	GPIO18	TF_CLK (SD Card)
31	GPIO19	MCU_MISO (SD Card)
32	NC	NA
33	GPIO21	CTP_INT* (Cap. Touchscreen) / Headers: P3 Pin 1, CN1 Pin 2
34	RXD0	RXD2 Header P1 Pin 3
35	TXD0	TXD2 Header P1 Pin 2
36	GPIO22	Header P3 Pin 2 (also Header CN1 Pin 3 on some boards)
37	GPIO23	MCU_MOSI (SD Card)
38	GND	Ground
39	GND	Ground

* Requires Hardware Mod

Hardware Mod (Add Hardware Interrupt for GT911)

NOTE: This only applies to the screen with the Capacitive touch panel (ESP32_3248S035C)

There is a routing mistake on the ESP32_3248S035C board that accidentally connects the Capacitive Touch Screen’s GT911 Interrupt pin to GND instead of through the R25 jumper to GPIO21. This means that the code has to use polling (by default) instead of hardware interrupts to determine when the screen is being touched. This results in excessive CPU utilization of greater than 80%. Making the below modifications results in a significantly reduced CPU utilization of under 10% on avg (on static screens).

Steps (see picture)

Cut the PCB trace going to the GT911’s INT pin (labeled as pin 5 on the flex cable). This disconnects GT911’s INT pin from GND.
Connect a bodge wire from the GT911’s INT pin to the closest side of R25 (connecting it to GPIO21).
Remove (pull-up) resistor R18 (GPIO21 to 3V3). The GT911’s INT pin is not strong enough to drive GPIO21 low with this resistor installed.

NOTE: Remember to enable the HARDWARE_MOD_GT911_INT option in CMakeLists.txt

Hardware Mod (Add External PSRAM)

This board has an external SOIC-8 footprint near the ESP32 module that is wired in parallel to the built-in SPI Flash. This can be used (with some modifications) to add an external SPI PSRAM in order to achieve more available memory.

NOTE: There are (at least) two revisions of this board.

On one revision, the external SOIC-8 footprint is populated with the SPI Flash IC. See Option 1 below for Mod details.
On another revision, the external SOIC-8 footprint is un-populated (the SPI flash is built into the ESP32 module). See Option 2 below for Mod details.

In either case, one will first need to acquire a compatible PSRAM IC. This can be desoldered from an existing board (i.e. ESP32-CAM board), or purchased separately. Make sure whatever IC you choose supports 3.3v and at least 80 MHz. Ideally it should support Quad SPI (QIO) as well.

Some compatible 8MB PSRAM ICs are:

ESP-PSRAM64H
IPS6404L-SQ-SPN
APM6404-SQ-SPN
APS6404L-3SQR-SN

NOTE: Remember to choose the correct variant in CMakeLists.txt to enable PSRAM support.

Option 1

On this revision, the PSRAM must be piggy-backed on top of the external Flash IC.

Place the PSRAM IC directly on top of the Flash IC (with the same orientation for Pin 1).
Connect all Pins (except for Pins 1 & 6) directly to the cooresponding pins on the Flash IC below.
Remove the RGB LED, as it conflicts with GPIO 16 & 17 that are needed for the new PSRAM IC.
Connect a bodge wire from Pin 1 to GPIO 16.
Connect a bodge wire from Pin 6 to GPIO 17.
Attach a 10k resistor between Pins 1 & 8 of the PSRAM IC. This is a pull-up resistor that ensures the PSRAM is deselected by default (i.e. when the Flash IC is in use).

Option 2

On this revision, the PSRAM can be soldered to the un-populated SOIC-8 footprint.

Cut the PCB trace going to Pin 1 as well as the PCB trace going to pin 6.
Solder the PSRAM IC to the SOIC-8 footprint (making sure Pin 1 is in the correct orientation).
Remove the RGB LED, as it conflicts with GPIO 16 & 17 that are needed for the new PSRAM IC.
Connect a bodge wire from Pin 1 to GPIO 16.
Connect a bodge wire from Pin 6 to GPIO 17.
Attach a 10k resistor between Pins 1 & 8 of the PSRAM IC. This is a pull-up resistor that ensures the PSRAM is deselected by default (i.e. when the Flash IC is in use).