What is GPIO?

GPIO (General Purpose Input/Output) pins are the physical connections on your tinyCore that let the ESP32-S3 interact with the outside world — turning things on and off, reading sensors, and communicating with other devices.

Why This Matters for Your Projects

Every time you wire up an LED, press a button, or plug in a sensor, you’re using GPIO pins. They’re the foundation of everything you’ll build with tinyCore. Understanding how they work (and which ones to use) will save you hours of debugging.

How GPIO Actually Works

Each GPIO pin on the ESP32-S3 can either send a voltage out or read a voltage in, depending on how you set it up in code.

Output Mode

When you set a pin as an output, the ESP32-S3 drives it to one of two voltage levels: 3.3V (HIGH) or 0V (LOW). That’s it — on or off. This is how you turn on an LED, trigger a relay, or send a signal to another device.

pinMode(5, OUTPUT);        // configure GPIO 5 as output
digitalWrite(5, HIGH);     // set to 3.3V (on)
digitalWrite(5, LOW);      // set to 0V (off)

Input Mode

When you set a pin as an input, the ESP32-S3 measures the voltage on that pin and tells you whether it’s HIGH (close to 3.3V) or LOW (close to 0V). This is how you detect button presses, read digital sensor outputs, or check the state of a signal.

pinMode(7, INPUT);                // configure GPIO 7 as input
int state = digitalRead(7);      // read the pin: HIGH or LOW

Analog Input

Some GPIO pins can also read analog values — voltages that fall anywhere between 0V and 3.3V. The ESP32-S3’s built-in ADC (Analog-to-Digital Converter) converts that voltage into a number from 0 to 4095. A reading of 0 means 0V, 4095 means 3.3V, and everything in between is proportional. This is how you read things like potentiometers, light sensors, and temperature probes.

int value = analogRead(1);    // read analog voltage on GPIO 1 (0–4095)

Note

The ESP32-S3 has two ADC units: ADC1 (GPIO 1–10) and ADC2 (GPIO 11–20). If your project uses WiFi, stick to ADC1 pins — ADC2 shares hardware with the WiFi radio and won’t give reliable readings when WiFi is active.

Pull-Up and Pull-Down Resistors

When a GPIO pin is set as an input but nothing is actively driving it HIGH or LOW, the pin is “floating.” A floating pin picks up random electrical noise and gives you unpredictable readings — your button will appear to randomly press itself. This is a real, common problem.

A pull-up resistor holds the pin at HIGH (3.3V) by default. When you press a button wired to GND, it overrides the resistor and pulls the pin LOW. A pull-down resistor does the opposite — holds the pin at LOW by default, and pressing a button wired to 3.3V drives it HIGH.

The ESP32-S3 has internal pull-up and pull-down resistors on every GPIO pin, so you don’t need to add external resistors for most cases. Just tell Arduino to enable them:

pinMode(7, INPUT_PULLUP);      // default HIGH, button pulls LOW
pinMode(7, INPUT_PULLDOWN);    // default LOW, button pulls HIGH

On the tinyCore

Reserved Pins

The tinyCore board uses certain GPIO pins for onboard hardware. These are already wired up, so you should avoid using them for other things unless you know what you’re doing:

Pin	Used For	Notes
GPIO 3	I2C SDA	Connected to QWIIC connectors and the IMU
GPIO 4	I2C SCL	Connected to QWIIC connectors and the IMU
GPIO 6	I2C Power	Set HIGH to power QWIIC sensors
GPIO 21	LED_BOOT	Onboard boot status LED
GPIO 33	LED_SIG	Onboard signal LED
SD Pins	SD Card	SPI bus for the microSD slot

Strapping Pins

Four GPIO pins are checked at startup to determine how the chip boots. If you have external circuits holding these pins at unexpected voltages during reset, the board might not start correctly:

Pin	Function	Default
GPIO 0	Boot mode (HIGH = normal, LOW = flash mode)	Internal pull-up (HIGH)
GPIO 45	Flash voltage (LOW = 3.3V, HIGH = 1.8V)	LOW
GPIO 46	Secondary boot mode	Internal pull-down (LOW)
GPIO 3	JTAG source	Floating (rarely relevant)

After boot completes, all strapping pins work as normal GPIO. Just be careful about what’s connected to them at power-on.

Flash and PSRAM Pins

GPIO 26–32 are used by the internal flash memory and should not be used. On S3 modules with octal PSRAM (like the ESP32-S3R8), GPIO 33–37 are also occupied.

Voltage: 3.3V Only

Caution

Every GPIO pin on the ESP32-S3 operates at 3.3V. The absolute maximum is 3.6V. Applying 5V to any pin will permanently damage the chip.

If you need to connect a 5V sensor or module, use a level shifter or voltage divider. When the ESP32-S3 outputs 3.3V, most 5V devices will still recognize it as HIGH — so level shifting is mainly needed for signals coming into the ESP32-S3.

Quick Reference

Feature	ESP32-S3
Total GPIO pins	GPIO 0–21, 26–48
Input-only pins	None (unlike the original ESP32)
Internal pull-up/pull-down	All GPIO pins
Logic voltage	3.3V
Max voltage tolerance	3.6V
ADC resolution	12-bit (0–4095)
ADC1 pins (WiFi-safe)	GPIO 1–10
ADC2 pins (no WiFi)	GPIO 11–20

Learn More

• Blink an LED — your first GPIO output project
• Read a Button Press — your first GPIO input project
• What is an ADC? — deep dive on analog readings
• What is PWM? — controlling LED brightness and motor speed with GPIO

Video: Introduction to ESP32

DroneBot Workshop — comprehensive ESP32 getting-started tutorial covering GPIO, analog I/O, WiFi, Bluetooth, and more. The first 15 minutes focus on GPIO and pin configuration.