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[中文]

ESP32 OLED Demo Walkthrough

Solution Features

The ESP32 OLED demo has the following features:

  • Collects temperature and humidity data
  • Connects to the internet and gets local time
  • Displays temperature/humidity data and local time on separate OLED screens
  • Switches screens through touch sensors or using touchless hand gestures
  • Enters low-power mode through touch sensor

The image belows shows an ESP32 development board with an OLED display.
screen demo

Hardware Preparation

This demo uses the ESP32_Button_Module_V2 as a development board that contains:

  • Proximity/ambient light sensor (APDS9960)
  • OLED display with 132 x 64 dot matrix panel(SSD1306)
  • Temperature/humidity sensor (HTS221)
  • Two touch sensor buttons

For the complete schematics of ESP32_Button_Module_V2, please click here.

The image below shows the section for power supply and power control of the screen and sensor.
apds9960

VDD33 is the output terminal of the LDO, with 3.3V power supply for ESP32, peripherals and flash. VDD33_PeriP is the power supply for the screen, temperature/humidity sensor and hand-gesture sensing module. The SI2301 transistor is used as a power switch that controls the voltage on VDD33_PeriP. By default, the transistor's gate terminal maintains a high level, that is, the power switch is turned off. You can turn it on by putting Power_ON to low level.

Software Design

The OLED display demo:

  • Uses esp-iot-solution development kit
  • Is based on FreeRTOS that supports multi-tasking
  • Gets local time with SNTP protocol
  • Enters low-power mode through touch sensor
  • Wakes up the device through touch sensor

Introduction to Low-power Mode

Hardware Design

To achieve a minimal power consumption in low-power mode, the solution implements:

  • Power control of screen, temperature/humidity sensor and hand-gesture sensing module
  • A low-power LDO with quiescent current of about 1 μA
  • Power management for the touch sensor

Touch Sensor Working Cycles

The touch sensor has two statuses: sleep and measurement. The touch sensor will sleep after each measurement. In normal working mode, the sleep period can be short, while in low-power mode, it can be long to reduce power consumption.

Call touch_pad_set_meas_time(uint16_t sleep_cycle, uint16_t meas_cycle) to set the sleep and measurement time before the touch sensor enters low-power mode.

Parameters:

  • sleep_cycle: sleep_cycle determines the interval between two measurements. t_sleep = sleep_cycle / (RTC_SLOW_CLK frequency)。

    Get the frequency value of RTC_SLOW_CLK by using rtc_clk_slow_freq_get_hz() function.

  • meas_cycle: meas_cycle determines the measurement time. t_meas = meas_cycle / 8M. The maximum value is 0xffff / 8M = 8.19 ms.

Low-power Mode

Long tap any touch sensor button to enable low-power mode. The sampling frequency is the lowest in this mode. Long tap the sensor button to release it from low-power mode. The images below show the current sampling waveforms.

  • Current sampling on LDO VOUT 3.3V (including the current consumption of ESP32, screen and touch sensor):
    figure_3.3V

Note: In low-power mode, the average current on LDO VOUT 3.3V is about 30 μA, while the maximum current is 1.6 mA, when the touch sensor is taking measurement.

  • Current sampling on LDO VIN 5V (including the current consumption of ESP32, screen, touch sensor and LDO):
    figure_5V

Note: In low-power mode, the average current on LDO VIN 5V is about 45 μA, while the maximum current is 2.1 mA.

Compile and Run the Demo

Preparation

Make sure you have installed the ESP32 toolchain on your PC. For the toolchain installation, you can refer to README.md.

Get IoT Solution Program Code

Run the following commands to download the iot-solution repository.

  • You can use the recursive option to automatically initialize all the submodules.

    git clone --recursive https://github.com/espressif/esp-iot-solution.git

  • You can also initialize the submodules manually, by first running:

    git clone https://github.com/espressif/esp-iot-solution.git

    • Then, switch to the root directory of the program and run the following command to get all the other dependent submodules.

      git submodule update --init --recursive

Compilation and Running

After downloading all the submodules, you can compile and run the oled_screen_module program. Go to the esp-iot-solution/examples/oled_screen_module directory, and follow the steps below:

  • Configure the settings for serial port.

Run the following command to configure the serial port settings. Set the port number and download speed by configuring Serial flasher config option.

    cd YOUR_IOT_SOLUTION_PATH/examples/oled_screen_module
    make menuconfig
  • Compile, download and run the program.

Run the following command to compile oled_screen_module. flash in the command enables downloading, while the optional monitor enables system printing.

    make flash monitor

Note: If the program cannot be downloaded automatically, you can download it mannually. After downloading, press the reset button on the board to run the program and check the logs on the serial port.