About ESP32 Wroom 32D
This chip is a powerful, generic WiFi + BT + BLE MCU module that targets a wide variety of applications, ranging from low-power sensor networks to the most demanding tasks, such as voice encoding, music streaming, and MP3 decoding.
Just like it, this module also has an ESP32-D0WD chip at its core. This chip has 2 CPU cores which can be individually controlled. The clock frequency is adjustable from 80 Mhz to 240 Mhz. The user can also power off the CPU and instead make use of the low-power co-processor to constantly monitor the peripheral changes or crossing of thresholds. This chip integrates a rich set of peripherals, from capacitive touch sensors, Hall sensors, SD Card interface, ethernet, high-speed SPI, UART, I2S, and I2C.
The integration of Bluetooth, Bluetooth LE, and WiFi ensures that a wide range of applications can be targeted and that the module is all-around. Using WiFi allows a large physical range and direct connection to the Internet through a WiFi router while using Bluetooth allows the user to conveniently connect to the phone or broadcast low-energy beacons for its detection.
The sleep current of the ESP32 chip is less than 5 µA. So, it’s suitable for battery-powered and wearable electronics applications. The module supports a data rate of up to 150 Mbps, and 20 dBm output power at the antenna to ensure the widest physical range. As such the module does offer industry-leading specifications and the best performance for electronic integration, range, power consumption, and connectivity.
Additionally, there are pins with specific features that make them suitable or not for a particular project. The following table shows what pins are best to use as inputs, outputs and which ones you need to be cautious.
The pins highlighted in green are OK to use. The ones highlighted in yellow are OK to use, but you need to pay attention because they may have an unexpected behavior mainly at boot. The pins highlighted in red are not recommended to use as inputs or outputs.
|0||pulled up||OK||outputs PWM signal at boot, must be LOW to enter flashing mode|
|1||TX pin||OK||debug output at boot|
|2||OK||OK||connected to on-board LED, must be left floating or LOW to enter flashing mode|
|3||OK||RX pin||HIGH at boot|
|5||OK||OK||outputs PWM signal at boot, strapping pin|
|6||x||x||connected to the integrated SPI flash|
|7||x||x||connected to the integrated SPI flash|
|8||x||x||connected to the integrated SPI flash|
|9||x||x||connected to the integrated SPI flash|
|10||x||x||connected to the integrated SPI flash|
|11||x||x||connected to the integrated SPI flash|
|12||OK||OK||boot fails if pulled high, strapping pin|
|14||OK||OK||outputs PWM signal at boot|
|15||OK||OK||outputs PWM signal at boot, strapping pin|
Continue reading for a more detail and in-depth analysis of the ESP32 GPIOs and its functions.
Input only pins
GPIOs 34 to 39 are GPIs – input only pins. These pins don’t have internal pull-up or pull-down resistors. They can’t be used as outputs, so use these pins only as inputs:
- GPIO 34
- GPIO 35
- GPIO 36
- GPIO 39
SPI flash integrated on the ESP-WROOM-32
GPIO 6 to GPIO 11 are exposed in some ESP32 development boards. However, these pins are connected to the integrated SPI flash on the ESP-WROOM-32 chip and are not recommended for other uses. So, don’t use these pins in your projects:
- GPIO 6 (SCK/CLK)
- GPIO 7 (SDO/SD0)
- GPIO 8 (SDI/SD1)
- GPIO 9 (SHD/SD2)
- GPIO 10 (SWP/SD3)
- GPIO 11 (CSC/CMD)
Capacitive touch GPIOs
The ESP32 has 10 internal capacitive touch sensors. These can sense variations in anything that holds an electrical charge, like the human skin. So they can detect variations induced when touching the GPIOs with a finger. These pins can be easily integrated into capacitive pads and replace mechanical buttons. The capacitive touch pins can also be used to wake up the ESP32 from deep sleep.
Those internal touch sensors are connected to these GPIOs:
- T0 (GPIO 4)
- T1 (GPIO 0)
- T2 (GPIO 2)
- T3 (GPIO 15)
- T4 (GPIO 13)
- T5 (GPIO 12)
- T6 (GPIO 14)
- T7 (GPIO 27)
- T8 (GPIO 33)
- T9 (GPIO 32)
Learn how to use the touch pins with Arduino IDE: ESP32 Touch Pins with Arduino IDE
Analog to Digital Converter (ADC)
The ESP32 has 18 x 12 bits ADC input channels (while the ESP8266 only has 1x 10 bits ADC). These are the GPIOs that can be used as ADC and respective channels:
- ADC1_CH0 (GPIO 36)
- ADC1_CH1 (GPIO 37)
- ADC1_CH2 (GPIO 38)
- ADC1_CH3 (GPIO 39)
- ADC1_CH4 (GPIO 32)
- ADC1_CH5 (GPIO 33)
- ADC1_CH6 (GPIO 34)
- ADC1_CH7 (GPIO 35)
- ADC2_CH0 (GPIO 4)
- ADC2_CH1 (GPIO 0)
- ADC2_CH2 (GPIO 2)
- ADC2_CH3 (GPIO 15)
- ADC2_CH4 (GPIO 13)
- ADC2_CH5 (GPIO 12)
- ADC2_CH6 (GPIO 14)
- ADC2_CH7 (GPIO 27)
- ADC2_CH8 (GPIO 25)
- ADC2_CH9 (GPIO 26)
Learn how to use the ESP32 ADC pins:
Note: ADC2 pins cannot be used when Wi-Fi is used. So, if you’re using Wi-Fi and you’re having trouble getting the value from an ADC2 GPIO, you may consider using an ADC1 GPIO instead. That should solve your problem.
The ADC input channels have a 12-bit resolution. This means that you can get analog readings ranging from 0 to 4095, in which 0 corresponds to 0V and 4095 to 3.3V. You can also set the resolution of your channels on the code and the ADC range.
The ESP32 ADC pins don’t have a linear behavior. You’ll probably won’t be able to distinguish between 0 and 0.1V, or between 3.2 and 3.3V. You need to keep that in mind when using the ADC pins. You’ll get a behavior similar to the one shown in the following figure.
Digital to Analog Converter (DAC)
There are 2 x 8 bits DAC channels on the ESP32 to convert digital signals into analog voltage signal outputs. These are the DAC channels:
- DAC1 (GPIO25)
- DAC2 (GPIO26)
There is RTC GPIO support on the ESP32. The GPIOs routed to the RTC low-power subsystem can be used when the ESP32 is in deep sleep. These RTC GPIOs can be used to wake up the ESP32 from deep sleep when the Ultra Low Power (ULP) co-processor is running. The following GPIOs can be used as an external wake up source.
- RTC_GPIO0 (GPIO36)
- RTC_GPIO3 (GPIO39)
- RTC_GPIO4 (GPIO34)
- RTC_GPIO5 (GPIO35)
- RTC_GPIO6 (GPIO25)
- RTC_GPIO7 (GPIO26)
- RTC_GPIO8 (GPIO33)
- RTC_GPIO9 (GPIO32)
- RTC_GPIO10 (GPIO4)
- RTC_GPIO11 (GPIO0)
- RTC_GPIO12 (GPIO2)
- RTC_GPIO13 (GPIO15)
- RTC_GPIO14 (GPIO13)
- RTC_GPIO15 (GPIO12)
- RTC_GPIO16 (GPIO14)
- RTC_GPIO17 (GPIO27)
Learn how to use the RTC GPIOs to wake up the ESP32 from deep sleep: ESP32 Deep Sleep with Arduino IDE and Wake Up Sources
The ESP32 LED PWM controller has 16 independent channels that can be configured to generate PWM signals with different properties. All pins that can act as outputs can be used as PWM pins (GPIOs 34 to 39 can’t generate PWM).
To set a PWM signal, you need to define these parameters in the code:
- Signal’s frequency;
- Duty cycle;
- PWM channel;
- GPIO where you want to output the signal.
Learn how to use ESP32 PWM with Arduino IDE: ESP32 PWM with Arduino IDE
The ESP32 has two I2C channels and any pin can be set as SDA or SCL. When using the ESP32 with the Arduino IDE, the default I2C pins are:
- GPIO 21 (SDA)
- GPIO 22 (SCL)
If you want to use other pins when using the wire library, you just need to call:
Learn more about I2C communication protocol with the ESP32 using Arduino IDE: ESP32 I2C Communication (Set Pins, Multiple Bus Interfaces and Peripherals)
By default, the pin mapping for SPI is:
|VSPI||GPIO 23||GPIO 19||GPIO 18||GPIO 5|
|HSPI||GPIO 13||GPIO 12||GPIO 14||GPIO 15|
Learn more about SPI communication protocol with the ESP32 using Arduino IDE: ESP32 SPI Communication: Set Pins, Multiple SPI Bus Interfaces, and Peripherals (Arduino IDE)
All GPIOs can be configured as interrupts.
Learn how to use interrupts with the ESP32:
The ESP32 chip has the following strapping pins:
- GPIO 0 (must be LOW to enter boot mode)
- GPIO 2 (must be floating or LOW during boot)
- GPIO 4
- GPIO 5 (must be HIGH during boot)
- GPIO 12 (must be LOW during boot)
- GPIO 15 (must be HIGH during boot)
These are used to put the ESP32 into bootloader or flashing mode. On most development boards with built-in USB/Serial, you don’t need to worry about the state of these pins. The board puts the pins in the right state for flashing or boot mode. More information on the ESP32 Boot Mode Selection can be found here.
However, if you have peripherals connected to those pins, you may have trouble trying to upload new code, flashing the ESP32 with new firmware, or resetting the board. If you have some peripherals connected to the strapping pins and you are getting trouble uploading code or flashing the ESP32, it may be because those peripherals are preventing the ESP32 from entering the right mode. Read the Boot Mode Selection documentation to guide you in the right direction. After resetting, flashing, or booting, those pins work as expected.
Pins HIGH at Boot
Some GPIOs change their state to HIGH or output PWM signals at boot or reset. This means that if you have outputs connected to these GPIOs you may get unexpected results when the ESP32 resets or boots.
- GPIO 1
- GPIO 3
- GPIO 5
- GPIO 6 to GPIO 11 (connected to the ESP32 integrated SPI flash memory – not recommended to use).
- GPIO 14
- GPIO 15
Enable (EN) is the 3.3V regulator’s enable pin. It’s pulled up, so connect to ground to disable the 3.3V regulator. This means that you can use this pin connected to a pushbutton to restart your ESP32, for example.
GPIO current drawn
The absolute maximum current drawn per GPIO is 40mA according to the “Recommended Operating Conditions” section in the ESP32 datasheet.
ESP32 Built-In Hall Effect Sensor
The ESP32 also features a built-in hall effect sensor that detects changes in the magnetic field in its surroundings.
We hope you’ve found this reference guide for the ESP32 GPIOs useful. If you have more tips about the ESP32 GPIOs, please share by writing a comment down below.
If you’re just getting started with the ESP32, we have some great content to get started:
- Learn ESP32 with Arduino IDE
- Getting Started with the ESP32 Development Board
- 20+ ESP32 Projects and Tutorials
- ESP32 Web Server Tutorial
- ESP32 vs ESP8266 – Pros and Cons
Thanks for reading.