ST7789

The ST7789 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). Many TFT display boards and ESP32 development boards with integrated display use this device driver.

The driver supports SPI and the Parallel interface, plus some lesser used ones.

Versions

Although ST7789 exists in a number of variants, there seem to be no substantial differences between the 2012 version ST7789S and the 2021 version ST7789P3. Apparently, the different versions are mere maintenance releases with minor hardware adjustments to chip size, pad locations, and supported voltage ranges.

The key display features remain identical:

The power consumption also remains identical.

That said, the data sheets are 300 pages+, filled with technical glibber and timing protocols. If you spot significant differences or know of compatibility issues, please leave a comment below.

Regardless of which ST7789 variant your display uses, they are all supported by the same libraries. If your display does not work, it is most likely due to incorrect GPIO assignments on your side, or due to incompatibilities between the display breakout board and your microcontroller (i.e. incompatible operating voltage, incompatible interface (Parallel instead of SPI), no exposed CS pin, etc.). It may help to test with different libraries (Adafruit, TFT_eSPI) as they use different default behaviors.

Programming

ESPHome Support

ESPHome started to support ST7789 with a dedicated component called ST7789V TFT LCD. This component has been made redundant since the ST7789 is now supported by the more generic ILI9XXX component.

platformio/Arduino Support

Adafruit provides a free Adafruit library for ST77* drivers (including the ST7789). It is also supported by TFT_eSPI.

Low Energy Modes

The ST7789 supports a low power sleep mode (SLEEP IN) in which power consumption drops from 6mA to 30uA. It is important to note that the display keeps working (although you cannot change its content in sleep mode).

This opens up exciting opportunities for low-power devices.

Deep Sleep

It is critical to send the ST7789 to its own SLEEP IN mode before you are sending your microcontroller to deep sleep. Else, the ST7789 would stay awake and continue to consume 4-6mA even though the microcontroller has switched to deep sleep.

Arduino & platformio

Here is the core of the code to effectively send an ESP32 and its display to sleep:

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

// instantiate the display controller using the Adafruit Library
Adafruit_ST7789 tft = Adafruit_ST7789(TFT_CS, TFT_DC, TFT_MOSI, TFT_SCLK, TFT_RST);

...

// 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

Likewise, to send an ESP32 and its display to power-efficient deep sleep in ESPHome, just a few lines of ESPHome code are needed.

Here is the example behavior to add to your *ESPHome device:**

• Deep Sleep Button: when you press the deep sleep button (in this example, GPIO0 is used to utilize 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 microcontroller and display wake up.

And this is the ESPHome code to add to your configuration to add the behavior to your ESPHome device:

# 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 ST7789 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 display 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 respect, 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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