ILI9341

The ILI9341 is a versatile TFT display driver IC commonly used for small to medium-sized displays with resolutions of up to 240x320 pixels at full 18bit color (262 thousand different colors). It is still a very popular TFT driver, however more modern drivers like the ST7789 are starting to replace it.

The ILI9341 is marginally less power efficient than its successors like the ST7789. It is slightly more affordable, though, so you find it in cheaper display designs.

Both drivers support the same major interfaces (like SPI), the same maximum resolution (240x320), the same 18-bit maximum colors, and can be controlled with the same software libraries (i.e. ESPHome ILI9xxx component).

Given the typical DIY use cases, both drivers can be used interchangeably for most projects.

Overview

Programming

ESPHome Support

ESPHome has dedicated support for ILI9341 through the ILI9XXX component.

PlatformIO/Arduino Support

• Adafruit ILI9341: specific library for this driver, well documented, enables the use of the hardware-neutral Adafruit GFX library on top of it
• TFT_eSPI: generic library for a wide range of TFT displays. Requires slightly confusing selection of the driver type you intend to use
• ucglib: universal library for color TFT displays, well documented, the ILI9341 driver is selected through the classes Ucglib_ILI9341_18x240x320_SWSPI and Ucglib_ILI9341_18x240x320_HWSPI.

Low Energy Modes

The ILI9341 supports a low power sleep mode (SLEEP IN) in which power consumption drops from 6mA to 100μA. Notably, the display content remains visible in sleep mode, although no updates can be made.

This feature makes the ILI9341 particularly useful for low-power devices, however the ST7789 is slightly more power efficient.

Deep Sleep

It is crucial to send the ILI9341 into SLEEP IN mode before putting your microcontroller into deep sleep. If omitted, the ILI9341 will continue drawing 4-6mA, even when the microcontroller is in deep sleep.

Arduino & PlatformIO

Here is an example of code to effectively send both an ESP32 and its display into deep sleep:

// define wakeup pin
esp_sleep_enable_ext0_wakeup(GPIO_NUM_35, 0);

// instantiate the display controller using the Adafruit Library
Adafruit_ILI9341 tft = Adafruit_ILI9341(TFT_CS, TFT_DC, TFT_MOSI, TFT_CLK, TFT_RST, TFT_MISO);

...

// send display to sleep:
tft.sendCommand(0x10);  // Send the SLEEP IN command
delay(120);             // Wait for the display to enter sleep mode
// Enter deep sleep
esp_deep_sleep_start();

ESPHome

To send an ESP32 and its display into power-efficient deep sleep in ESPHome, only a few lines of ESPHome code are required.

Here is an example of the behavior to add to your ESPHome device:

• Deep Sleep Button: When you press the deep sleep button (in this example, GPIO0 is used to leverage the existing boot button) for more than 3 seconds, the system enters the most power-efficient deep sleep mode (and sends the display to sleep as well).
• Wake-Up Button: When you press the wake-up button (assigned to GPIO35 low active in this example), both the microcontroller and display will wake up.

Here is the ESPHome code to add to your configuration for this functionality:

# enable deep sleep capabilities and set wakeup-pin (GPIO35) in energy-efficient ext1 mode
deep_sleep:
  id: deep_sleep_control
  esp32_ext1_wakeup:       # uses much less deep sleep power than wakeup_pin:
    pins:
      - number: 35
    mode: ALL_LOW 

# perform all necessary actions to send peripherals to deep sleep
script:
  - id: prepare_for_sleep
    then:
      # switch display controller in sleep mode:
      - lambda: |-
          // Send display to sleep before deep sleep
          uint8_t command = 0x10;  // Your command
          id(display1).command(command);
      - delay: 120ms    
      # send esp32 to deep sleep:
      - deep_sleep.enter: deep_sleep_control

# button to invoke deep sleep (in this case, the *boot* button is used)
binary_sensor:
  - platform: gpio
    name: "Deep Sleep Button"
    id: deep_sleep_button

    pin:
        number: GPIO0
        # low active:
        inverted: True
        mode:
        input: True
        pullup: True

    # debounce:
    filters: 
        - delayed_on: 10ms
        - delayed_off: 10ms  

    # super long press (>3s) without need to release
    on_multi_click:
        - timing:
            - ON for at least 3.1s
            then:
            # invoke deep sleep
            - script.execute: prepare_for_sleep

Low Power Display Operations

When your device needs to display static content, you can send the ST7789 to its SLEEP IN mode. The display continues to show its content.

By cleverly sending the ILI9341 to its own sleep mode when you don’t need screen updates, and waking it up via SLEEP OUT only temporarily for screen updates, you can minimize the power consumption of your device by roughly 4-6mA.

Show Display During Deep Sleep

You can even keep the display on during deep sleep. In fact, the display remained on in all of the examples above. The reason why you did not see any display content was that the display backlight was turned off.

When you power the display backlight via a GPIO pin, in the most efficient deep sleep modes, all GPIOs go low, so the display backlight is turned off.

While you could choose a less efficient deep sleep mode for your ESP32 and keep the backlight GPIO active, this is not the most power-efficient approach. Instead, you should power the backlight pin independently from the microcontroller, either by directly connecting it to a positive voltage (depending on the display breakout board you are using), or via a current-limiting resistor (or potentiometer to manually adjust brightness).

This way, when you send your device to full deep sleep, the display would still show its last content. The total power consumption would just be the backlight current (which can be as low as 20mA), and the deep sleep current (with a highly efficient FireBeetle ESP32 breakout board, this would be 12uA, whereas a Lolin32 Lite would require 350uA).

ESP32 With Active Display At 20mA

In any case, your deep sleeping device would have a running display with static content at just about 20mA power consumption (with basically only the backlight LEDs consuming power).

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