Lights that move on their own
Nine of the thirty-six GPIOs are already busy on the ESP32-S3 before your sketch touches them — the serial port, the native USB socket, the memory inside the module, the BOOT button and the RGB LED — and every one has an LED on the shield. Here is what each does, and which to leave alone.
Before your sketch runs
Plug the board in with nothing uploaded and look at the shield. Most LEDs shimmer or sit half-lit — those are floating, the subject of the previous page. A few are steady from the first instant, and they are the interesting ones.
setup() gets to them.The ESP32-S3's datasheet lists which pins it pulls up or down itself at reset. GPIO 0, 43 and 44 are pulled up, so their LEDs light. GPIO 45 and 46 are pulled down, so theirs stay dark. GPIO 20 has the USB pull-up, and lights too. The shield's inverter inputs do not disturb any of that: the datasheet says these defaults hold with nothing attached or with "an external high-impedance circuit", which is what an inverter input is.
The serial port: 43 and 44
The left-hand USB socket on the ESP32-S3 goes to a USB-serial chip, which talks to the S3 over two wires: GPIO 43 out and GPIO 44 in. A serial line rests HIGH, so both LEDs are normally lit.
Print something and LED 43 flickers dark. Upload a sketch through that socket and LED 44 flickers while the new program arrives. It is the most useful activity light on the board, and both pins are hands off in your own wiring.
The native USB socket: 19 and 20
The right-hand USB socket is wired straight to the S3 on GPIO 19 and GPIO 20. With a cable in that socket, both LEDs flicker while the computer and the board talk. Use either pin for something else and that socket stops working.
The memory: 35, 36 and 37
The kit's ESP32-S3 is an N16R8: 16 MB of flash and 8 MB of PSRAM, the extra memory that large programs and screens need. That PSRAM uses a fast bus inside the module, and GPIO 35, 36 and 37 are three of its lines. They still come out to the header, so the shield still gives them LEDs, which may flicker or glow while a sketch uses memory.
Never drive them. The program is running in that memory.
The two you can use with care: 0 and 48
GPIO 0 is the BOOT button, held HIGH by a resistor on the ESP32-S3. Its LED is lit and goes out while you hold BOOT, which is a quick way to see the shield working without uploading anything. After the board has started, GPIO 0 is an ordinary pin — but anything that holds it LOW at the moment of reset stops your sketch starting.
GPIO 48 is the data line of the RGB LED on the ESP32-S3. Its LED blinks briefly whenever that RGB LED is set. You can use the pin, and the RGB LED will show a colour you did not ask for.
When it does not work
GPIO 43 is the transmit line of the serial port behind the left-hand USB socket. It rests HIGH, so the LED is lit, and each character pulls it LOW in quick bursts. That is the serial port working, and a free activity light.
Those two pins are the serial link to your computer. Setting either as an output or using it for something else takes the Serial Monitor down, and on the left-hand socket it takes uploads down too. Move that wire to a pin that is not spoken for.
On the N16R8 module in this kit those three pins carry the 8 MB of PSRAM inside the module. Driving one corrupts the memory the program is running in. Use any other GPIO; the shield's LEDs on 35 to 37 are only for watching.
GPIO 0 is the BOOT button, held HIGH by a 10 kΩ resistor on the ESP32-S3. The LED goes out while the button is pressed. If it stays out, something wired to row 0 is pulling it LOW, which also stops the board booting your sketch at the next reset.
Those are that socket's two data wires. Using them as ordinary pins disconnects the socket. Re-upload through the left-hand socket, which uses GPIO 43 and 44 instead, and pick different pins in your sketch.
All 36 GPIOs, what the marks beside them mean, and which are already spoken for.
The pins at the edge →Edit this page — content/books/esp32s3-base/lights-that-move-on-their-own.mdx
Questions people ask first
Which way round does the ESP32-S3 go on the base?
Its USB sockets go over the two boxes printed USB, at the bottom of the base, with the antenna end at the top under the display connector.
Nothing stops the other way: the two sockets are identical, so the board seats just as firmly end for end. Put in backwards, its 3.3 V regulator output ends up wired to ground, and the board can be damaged for good. Seat the board first and plug the USB cable in second, every time.
Where does the power for my sensors come from?
The base has no regulator, no battery connector and no power input. It is powered through the ESP32-S3's own USB sockets, and every power way on it is one of that board's pins carried out.
The 3V3 ways are the output of the regulator on the ESP32-S3. The 5V ways are the board's 5V pin: about 4.6 V with a USB cable plugged in, and nothing without one. Nothing on the way is switched, fused or filtered.
Can I run a motor, relay or LED strip from the base?
Not from its power ways. Motors, relays, servos and long LED strips need their own supply, with its ground joined to a GND way on the base, because the ESP32-S3's regulator is small and is also running your sketch.
Small sensors and a display can take 3V3 and ground from the base. No current rating is quoted for the ways, because none has been checked.
How many GPIOs does the Pluggable Terminal Base bring out?
24 of the ESP32-S3 Gold's 36 GPIOs, once each, on two 12-way push-in blocks, plus two 4-way power blocks.
Twelve do not come out: 0, 1, 2, 3, 4, 35, 36, 37, 43, 44, 45 and 46, and the RST pin. GPIO 1, 2 and 4 reach the display connector and nothing else. All of the I²C and SPI pins are on the left block, and GPIO 19 and 20 (the native USB pair, on the right block) should be left alone while a sketch is using USB.
How many GPIOs does the Screw Terminal Base bring out?
26 of the ESP32-S3's GPIOs, once each, on two 15-way screw terminal blocks, with 3V3 on the left block and 5V on the right. Ten GPIOs do not come out.
The native USB pins (GPIO 19 and 20) are on the right block: a wire on either one shares the USB lines with the computer, so leave them alone unless the sketch is not using native USB.
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