In the previous entry, we looked in detail at the different pins of the ESP32, as well as their specific functions and utilities.
However, just like with the ESP8266, not all pins of the ESP32 are equally safe to use in our projects.
This is because some pins perform specific roles or participate in the device’s boot process. Incorrectly using these pins can cause conflicts that prevent your project from working, or even break something.
If you are using an ESP32-S3, you have a similar summary in this entry What pins can I use on an ESP32-S3
Pin Summary
Therefore, it is very useful to have a reference table that provides clear and precise information about which pins are safe for use and which have specific functions.
I recommend keeping this table handy and consulting it before starting a project with an ESP32, to avoid surprises from using a pin that we shouldn’t.
[ { “gpio”: 0, “name”: “IO0”, “funcs”: [“GPIO0”, “ADC2_CH1”, “TOUCH_CH1”, “PWM”], “tags”: [“Boot”, “PullUp”], “note”: “⚠️ HIGH at startup. LOW for flashing.”, “status”: “warn” }, { “gpio”: 1, “name”: “TX”, “funcs”: [“GPIO1”, “U0TXD”], “tags”: [“Debug”], “note”: ”❌ TX pin. Debug output at startup.”, “status”: “danger” }, { “gpio”: 2, “name”: “IO2”, “funcs”: [“GPIO2”, “ADC2_CH2”, “TOUCH_CH2”], “tags”: [“LED”, “Boot”], “note”: “⚠️ Floating/LOW for flashing. Connected to LED.”, “status”: “warn” }, { “gpio”: 3, “name”: “RX”, “funcs”: [“GPIO3”, “U0RXD”], “tags”: [“Debug”], “note”: ”❌ RX pin. HIGH at startup.”, “status”: “danger” }, { “gpio”: 4, “name”: “IO4”, “funcs”: [“GPIO4”, “ADC2_CH0”, “TOUCH_CH0”], “tags”: [], “note”: “✔️ Safe for general use.”, “status”: “safe” }, { “gpio”: 5, “name”: “IO5”, “funcs”: [“GPIO5”, “PWM”], “tags”: [“Boot”], “note”: “⚠️ Must be HIGH at startup.”, “status”: “warn” }, { “gpio”: 6, “name”: “CLK”, “funcs”: [“GPIO6”, “SPI_CLK”], “tags”: [“Flash”], “note”: ”❌ Reserved for Flash SPI.”, “status”: “danger” }, { “gpio”: 7, “name”: “D0”, “funcs”: [“GPIO7”, “SPI_Q”], “tags”: [“Flash”], “note”: ”❌ Reserved for Flash SPI.”, “status”: “danger” }, { “gpio”: 8, “name”: “D1”, “funcs”: [“GPIO8”, “SPI_D”], “tags”: [“Flash”], “note”: ”❌ Reserved for Flash SPI.”, “status”: “danger” }, { “gpio”: 9, “name”: “D2”, “funcs”: [“GPIO9”, “SPI_HD”], “tags”: [“Flash”], “note”: ”❌ Reserved for Flash SPI.”, “status”: “danger” }, { “gpio”: 10, “name”: “D3”, “funcs”: [“GPIO10”, “SPI_WP”], “tags”: [“Flash”], “note”: ”❌ Reserved for Flash SPI.”, “status”: “danger” }, { “gpio”: 11, “name”: “CMD”, “funcs”: [“GPIO11”, “SPI_CS0”], “tags”: [“Flash”], “note”: ”❌ Reserved for Flash SPI.”, “status”: “danger” }, { “gpio”: 12, “name”: “IO12”, “funcs”: [“GPIO12”, “ADC2_CH5”, “TOUCH_CH5”, “MTDI”], “tags”: [“Boot”, “JTAG”], “note”: “⚠️ Must be LOW at startup (LDO voltage).”, “status”: “warn” }, { “gpio”: 13, “name”: “IO13”, “funcs”: [“GPIO13”, “ADC2_CH4”, “TOUCH_CH4”, “MTCK”], “tags”: [“JTAG”], “note”: “✔️ JTAG debug.”, “status”: “safe” }, { “gpio”: 14, “name”: “IO14”, “funcs”: [“GPIO14”, “ADC2_CH6”, “TOUCH_CH6”, “MTMS”, “PWM”], “tags”: [“JTAG”], “note”: “⚠️ PWM at startup.”, “status”: “warn” }, { “gpio”: 15, “name”: “IO15”, “funcs”: [“GPIO15”, “ADC2_CH3”, “TOUCH_CH3”, “MTDO”], “tags”: [“Boot”, “JTAG”], “note”: “⚠️ Must be HIGH at startup.”, “status”: “warn” }, { “gpio”: 16, “name”: “IO16”, “funcs”: [“GPIO16”], “tags”: [], “note”: “✔️ Safe for general use.”, “status”: “safe” }, { “gpio”: 17, “name”: “IO17”, “funcs”: [“GPIO17”], “tags”: [], “note”: “✔️ Safe for general use.”, “status”: “safe” }, { “gpio”: 18, “name”: “IO18”, “funcs”: [“GPIO18”], “tags”: [], “note”: “✔️ Safe for general use.”, “status”: “safe” }, { “gpio”: 19, “name”: “IO19”, “funcs”: [“GPIO19”], “tags”: [], “note”: “✔️ Safe for general use.”, “status”: “safe” }, { “gpio”: 21, “name”: “IO21”, “funcs”: [“GPIO21”, “I2C_SDA”], “tags”: [“I2C”], “note”: “✔️ Standard I2C SDA.”, “status”: “safe” }, { “gpio”: 22, “name”: “IO22”, “funcs”: [“GPIO22”, “I2C_SCL”], “tags”: [“I2C”], “note”: “✔️ Standard I2C SCL.”, “status”: “safe” }, { “gpio”: 23, “name”: “IO23”, “funcs”: [“GPIO23”], “tags”: [], “note”: “✔️ Safe for general use.”, “status”: “safe” }, { “gpio”: 25, “name”: “IO25”, “funcs”: [“GPIO25”, “ADC1_CH8”, “DAC_1”], “tags”: [“DAC”], “note”: “✔️ Safe. DAC output.”, “status”: “safe” }, { “gpio”: 26, “name”: “IO26”, “funcs”: [“GPIO26”, “ADC2_CH9”, “DAC_2”], “tags”: [“DAC”], “note”: “✔️ Safe. DAC output.”, “status”: “safe” }, { “gpio”: 27, “name”: “IO27”, “funcs”: [“GPIO27”, “ADC2_CH7”, “TOUCH_CH7”], “tags”: [], “note”: “✔️ Safe for general use.”, “status”: “safe” }, { “gpio”: 32, “name”: “IO32”, “funcs”: [“GPIO32”, “ADC1_CH4”, “TOUCH_CH9”], “tags”: [], “note”: “✔️ Safe for general use.”, “status”: “safe” }, { “gpio”: 33, “name”: “IO33”, “funcs”: [“GPIO33”, “ADC1_CH5”, “TOUCH_CH8”], “tags”: [], “note”: “✔️ Safe for general use.”, “status”: “safe” }, { “gpio”: 34, “name”: “IO34”, “funcs”: [“GPIO34”, “ADC1_CH6”], “tags”: [“InputOnly”], “note”: “⚠️ Input Only.”, “status”: “warn” }, { “gpio”: 35, “name”: “IO35”, “funcs”: [“GPIO35”, “ADC1_CH7”], “tags”: [“InputOnly”], “note”: “⚠️ Input Only.”, “status”: “warn” }, { “gpio”: 36, “name”: “VP”, “funcs”: [“GPIO36”, “ADC1_CH0”], “tags”: [“InputOnly”], “note”: “⚠️ Input Only.”, “status”: “warn” }, { “gpio”: 39, “name”: “VN”, “funcs”: [“GPIO39”, “ADC1_CH3”], “tags”: [“InputOnly”], “note”: “⚠️ Input Only.”, “status”: “warn” } ]
