MicroPython Programming Tutorial: Getting Started with the ESP32 Thing
Shawn Hymel 
Hardware Overview
ESP32 Thing Pinout
The ESP32 has a number of features, such as:
- 18 analog-to-digital converter (ADC) channels
- 3 SPI interfaces
- 3 UART interfaces
- 2 I2C interfaces
- 16 PWM outputs
- 2 digital-to-analog converters (DAC)
- 2 I2S interfaces
One I2C, two of the UART interfaces, and one of the SPI interfaces can be assigned to any pin your project requires. However, there are a few hardware features (namely the ADC and DAC) that are assigned static pins. The graphical reference below helps demonstrate where you can find those peripherals.
Input Only Pins: 34-39
Pins 34, 35, 36, 37, 38 and 39 cannot be configured as outputs, but they can be used as either digital inputs, analog inputs, or for other unique purposes. Also note that they do not have internal pull-up or pull-down resistors, like the other I/O pins.
GPIO pins 36-39 are an integral part of the ultra low noise pre-amplifier for the ADC – they are wired up to 270pF capacitors, which help to configure the sampling time and noise of the pre-amp.
From the ESP32 Thing Schematic: GPIO 36-39 are tied together with caps. Those and pins 34 and 35 are input only!
ESP32 Thing Board Overview
The ESP32 Thing breaks out most of the pins on the ESP32 chip and gives you access to a few extra features, such as a LiPo battery charger, 4 MB of flash memory, an FTDI USB-to-Serial chip, and a user-controlled LED and button.
Powering the ESP32 Thing
The easiest ways to power the ESP32 Thing is through either the onboard USB connector or through the single-cell LiPo battery connector. Note that if a battery and USB are connected at the same time, the USB connection will charge the LiPo at a rate up to 500 mA.
⚡ The ESP32's operating voltage range is 2.2 to 3.6V. Under normal operation the ESP32 Thing will power the chip at 3.3V. The I/O pins are not 5V-tolerant! If you interface the board with 5V (or higher) components, you'll need to do some level shifting.
The 3.3V regulator on the ESP32 Thing can reliably supply up to 600mA, which should be more than enough overhead for most projects. The ESP32 can pull as much as 250mA during RF transmissions, but we've generally measured it to consume around 150mA, even while actively transmitting over WiFi. The output of the regulator is also broken out to the sides of the board (the pins labeled 3V3). These power pins can be used to supply external components.
In addition to USB and battery connectors, the VBAT, and VUSB pins are all broken out to both sides of the board. These pins can be used as an alternative supply input to the ESP32 Thing. The maximum, allowable voltage input to VUSB is 6V, and VBAT should not be connected to anything other than a single-cell LiPo battery. Alternatively, if you have a regulated voltage source between 2.2V and 3.6V, the "3V3" lines can be used to directly supply the ESP32 and its peripherals.