Testing the new ESP32-S2

I got one ESP32-S2 Saola board and I will be making some tests on this repository:


ESP32-S2 integrates a rich set of peripherals, with 43 programmable GPIOs which can be flexibly configured to provide USB OTG, LCD interface, camera interface, SPI, I2S, UART, ADC, DAC and other common functionality. ESP32-S2 provides the optimal HMI solution for touchscreen and touchpad-based devices.
The arduino-espressif32 is getting it’s finals touches of grace before being available and I will just do a small repository and try to test as much as I can and also make some benchmark comparisons.

In the first tests the impression is that most of the arduino framework is already working with a few exceptions. Not all the features are supported yet but they will be soon.
Sadly the deepsleep is still not optimized correctly in this first revisions of the Saola board and on 3.4 v I measured 0.79 mA/hour. On a good ESP32 board like tinyPICO it’s 0.08 mA/hour (10 times less) now that’s something you can plug to a battery and make it wake up every hour to do something.
Please note this is not a fair comparison at this point. It’s only a test with same firmware, same conditions and bypassing power regulator to see how much it consumes directly powering the board with the 3.3V pin.
On the other hand, making processor intensive tests like receiving UDP packets or receiving and decompressing at the same time, it showed similar speed with much less consumption than the ESP32.

But other than this small annoyance in this first board revision it’s a really promising product and very powerful System on a Chip. The feature list is impressive:

  • Xtensa® single-core 32-bit LX7 microcontroller
  • 43 programmable GPIOs.
  • Standard peripherals including SPI, I2C, I2S, UART, ADC/DAC and PWM.
  • LCD (8-bit parallel RGB/8080/6800) interface and also support for 16/24-bit parallel.
  • Camera interface supports 8 or 16-bit DVP image sensor, with clock frequency of up to 40 MHz.

Please follow the repository and add issues or just leave a comment here if you want me to test any of the features and I will publish the results. Note that the only condition is that the results should be shared with the community on the internet. It’s all open-source, so we will keep the same spirit and share the results with everyone else.
Another example of ESP32-S2 in action, controlling 144 RGB Neopixels using Makuna library https://twitter.com/martinfasani/status/1267015931689144320

What GPIOs not to use in ESP32-S2

GPIODescription / default configuration
26PSRAM pin
46Pull-down – INPUT only
43 *default UART0 pin on S2
44 *default UART0 pin on S2
NOTE: GPIO26 it applies primarily to WROVER as those come with PSRAM.
* not sure if you should not use 43,44 but if you will use UART0 output in your project is the best you don’t use them

Important documentation
ESP32-S2 Technical reference manual (page 39-40 for the not-use GPIOs)

Arduino-esp32 course – General-purpose input/output (GPIO) – Chapter 3

I want to state here that I’m not an electronics engineer and I know the basics only after years of tinkering and because I use to soldier PCBs for my father since I’m 8 or so. So if there is anything that is not correctly explained just comment and I will try to document it better.
The ESP8266 has 17 GPIO pins (0-16), however, you can only use 11 of them, because 6 pins (GPIO 6 – 11) are used to connect the flash memory chip.
The ESP32 chip has 40 physical GPIO pins. Not all of them can be used and some of them are only input GPIOs meaning you cannot use them for output communication (Refer to your board tech specs fot that) According to Espressif documentation on the ESP32:

  • GPIO 6-11 are usually used for SPI flash.
  • GPIO 34-39 can only be set as input mode and do not have software pullup or pulldown functions.

Electronics ABC
pull-up resistor connects unused input pins to the dc supply voltage, (3.3 Vcc in ESP32) to keep the given input HIGH
pull-down resistor connects unused input pins to ground, (GND 0V) to keep the given input LOW.
Analog-to-Digital Converter (ADC)
The Esp32 integrates 12-bit ADCs and supports measurements on 18 channels (analog-enabled pins). The Ultra low power (ULP-coprocessor) in the ESP32 is also designed to measure voltages while operating in sleep mode, which allows for low power consumption.
Digital-to-Analog Converter (DAC)
Two 8-bit DAC channels can be used to convert two digital signals to two analog voltage outputs. These dual DACs support the power supply as an input voltage reference and can drive other circuits. Dual channels support independent conversions.

A detailed walkthrough over GPIOs and electronics is out-of-scope in this blog post series since it’s a thema on it’s own and I think a engineer could be the best suited to expand on this properly. There are many instructables and videos about it if you are interested in researching more.

So now back to ESP32 Arduino framework coding, let’s use this GPIO information, to declare one as output and blink a LED.

#include "Arduino.h"
// HINT: Many ESP32 boards have an internal LED on GPIO5
// If it's on another PIN just change it here:
int ledGpio = 5; 

void setup() { 
  Serial.println("Hello blinking LED");
  pinMode(ledGpio, OUTPUT);
void loop() { 
  digitalWrite(ledGpio, HIGH); 
  digitalWrite(ledGpio, LOW); 

As a good reference here is the pinMode entry in Arduino documentation. modes can be:


This very short program will just set the GPIO5 in output mode and in the loop just turn it HIGH(1) and send 3.3V to the GPIO or LOW(0). Keep in mind that the ESP32 can draw a max. consumtion of about 10 mA per GPIO so always use a resistance (10K or similar) if you connect your own LED or you may damage the board.
Now seeing that the GPIO state is 1 or 0, we can also write this program in a shorter way, let’s give it a second round:

include "Arduino.h"
int ledGpio = 25;
bool ledState = 0; // New bool variable
void setup() {
  pinMode(ledGpio, OUTPUT);
void loop() {
  digitalWrite(ledGpio, ledState);
  ledState = !ledState;

We are just doing one digitalWrite per loop now and right after that just redeclaring the variable using the logical NOT operator. That way it will flip between 0 and 1, turning the LED on and off quite fast since we added just a 20 millis delay. So fast is almost always on!
So now we are in this point we can start with the next topic that is called pulse width modulation or PWM.

PWM provides the ability to ‘simulate’ varying levels of power by oscillating the output from the microcontroller. By varying (or ‘modulating’) the pulsing width we can effectively control the light output from the LED, hence the term PWM or Pulse Width Modulation. Arduino also had PWM pins with a scale from 0 – 255 so we could have 255 brightness level on a LED.

This PWM image is from Arduino tutorial – credits: https://www.arduino.cc/en/tutorial/PWM

ESP32 / ESP8266 PWM example for one Channel

// Since someone asked about a modern AnalogWrite PWM example
// Just try to compile this one
include "Arduino.h"

// use first channel of 16 channels (started from zero)
define LEDC_CHANNEL_0 0
// use 13 bit precission for LEDC timer
define LEDC_TIMER_13_BIT 13
// use 5000 Hz as a LEDC base frequency
define LEDC_BASE_FREQ 5000
// fade LED PIN (replace with LED_BUILTIN constant for built-in LED)
define LED_PIN 25
bool brightDirection = 0;
int ledBright = 0;

void setup() {
  Serial.println("Hello PWM LED");
  // Setup timer and attach timer to a led pin
  ledcAttachPin(LED_PIN, LEDC_CHANNEL_0);
// Arduino like analogWrite: value has to be between 0 and valueMax
void ledcAnalogWrite(uint8_t channel, uint32_t value, uint32_t valueMax = 255) {
  // calculate duty, 8191 from 2 ^ 13 - 1
  uint32_t duty = (8191 / valueMax) * min(value, valueMax);
  ledcWrite(channel, duty);

void loop() {
  // set the brightness on LEDC channel 0
  ledcAnalogWrite(LEDC_CHANNEL_0, ledBright);
  if (ledBright == 255 || ledBright == 0) {
    brightDirection = !brightDirection;
  if (brightDirection) {
  } else {

The ESP32 has a PWM controller with 16 independent channels that can be configured to generate PWM signals with different properties. Just wanted to mention this possibility but I’m not going to extend myself in this topic since they are hundred of pages that explain it much better than I could do. Please check https://randomnerdtutorials.com/esp32-pwm-arduino-ide to have a nice PWM example.

Keep tuned and follow this blog to get more. In next chapter we are going to explore I2C communication and connect a thermometer to our ESP32 to display via Serial the room temperature.