ESP32-S3 board
The brain — and today, the radio.
01 First, know the pieces
What you need
Just the board and its USB cable from the kit — plus your phone. Today's extra tool is a free app called LightBlue (iOS App Store or Google Play) that speaks BLE and lets you see exactly what the board broadcasts. Tap Define on anything unfamiliar — the answer opens as a field note you can read and dismiss without losing your place.
Arduino IDE
Uploads the sketch and opens Serial Monitor.
Official sketch
Sketch_20.1_BLE_USART.ino
02 One action at a time
Build it
Two ends today — the board end in Serial Monitor and the phone end in LightBlue. Tap each step as you go to keep your place; you can finish without opening a single field note.
0 / 10 done
On your phone, install the free LightBlue app from the iOS App Store or Google Play, and turn Bluetooth on. (On Android, Serial Bluetooth Terminal also works if you already have it.)
Plug the ESP32-S3 into your computer with a data-capable USB cable.
Open
Sketch_20.1_BLE_USART.inoin Arduino IDE — the BLE libraries ship with the ESP32 board package, so there is nothing extra to install.Press Upload, then open Serial Monitor and set the baud rate to
115200.Watch for
Waiting a client connection to notify...— the board is now broadcasting its name.In LightBlue, open the Scan page, swipe down to refresh, and tap ESP32S3_Bluetooth. BLE devices are opened inside a GATT app like this — the name never shows up in your phone's Settings→Bluetooth pairing list.
To hear the board, open the characteristic ending 0003, set Data Format to
utf-string, and tap Subscribe.Type a line in Serial Monitor's send box and press Enter — it appears on the phone.
To talk back, open the characteristic ending 0002, set Data Format to
utf-string, type a message, and tap Write.Watch your message appear in Serial Monitor.
03 Read just enough code
Read the code
The sketch is about seventy lines; the parts that matter fit here. A helper called setupBLE() builds the radio's public face — it creates the service with a write characteristic for phone→board and a notify characteristic for board→phone, then starts advertising. The BLE libraries ship with the ESP32 board package, so it compiles as-is.
#include "BLEDevice.h"
#include "BLEServer.h"
#define SERVICE_UUID "6E400001-B5A3-F393-E0A9-E50E24DCCA9E"
#define CHARACTERISTIC_UUID_RX "6E400002-B5A3-F393-E0A9-E50E24DCCA9E"
#define CHARACTERISTIC_UUID_TX "6E400003-B5A3-F393-E0A9-E50E24DCCA9E"
void setup() {
Serial.begin(115200);
setupBLE("ESP32S3_Bluetooth");
}
void loop() {
long now = millis();
if (now - lastMsg > 100) {
if (deviceConnected&&rxload.length()>0) {
Serial.println(rxload);
rxload="";
}
if(Serial.available()>0){
String str=Serial.readString();
const char *newValue=str.c_str();
pCharacteristic->setValue(newValue);
pCharacteristic->notify();
}
lastMsg = now;
}
}setupBLE("ESP32S3_Bluetooth")The helper shown in the full sketch. It creates the service with a write characteristic for phone→board and a notify characteristic for board→phone, then starts advertising this name. #define CHARACTERISTIC_UUID_RX …UUIDs are the fixed names each side looks up to find the right data lane — this trio is the widely adopted Nordic UART set. Serial.println(rxload)Whatever the phone wrote arrives in rxload and prints straight to Serial Monitor. pCharacteristic->notify()Pushes whatever you typed in Serial Monitor out over the radio to every subscribed phone. Optional side path · no wiring
_UART_UUID = bluetooth.UUID("6E400001-B5A3-F393-E0A9-E50E24DCCA9E")
p = BLESimplePeripheral(ble)
p.on_write(on_rx)
print("Please use LightBlue to connect to ESP32S3.")
tx_data = input("Enter anything: ")
p.send(tx_data)_UART_UUID = bluetooth.UUID("6E400001-…")The same Nordic UART service UUID as the Arduino sketch — the phone app sees the same service either way.p.on_write(on_rx)Registers the function that runs whenever the phone writes — the Python side of the pass-through.Copy ble_advertising.py onto the board alongside BLE.py — the script imports it. This version broadcasts the shorter name ESP32S3, so scan for that in LightBlue. If MicroPython isn't set up yet, skip this — it should never block the Arduino-first day.
04 Understand, don't memorise
A serial pipe over radio
BLE organises everything a device offers into services, and each service into characteristics — small named mailboxes the phone can read, write, or subscribe to. Today's service holds exactly two, one for each direction.
The board calls out
The sketch broadcasts the name ESP32S3_Bluetooth so nearby phones can find it.
The phone answers
LightBlue opens a connection and finds the service by its UUID.
Phone → board
Text written to the characteristic ending 0002 lands in the sketch and prints to Serial Monitor.
Board → phone
Text typed in Serial Monitor is pushed through the characteristic ending 0003 to every subscriber.
Useful model
one write lane in + one notify lane out = a two-way text pipe
Why the long UUIDs
A UUID is a name long enough that nobody else's gadget will ever share it by accident. This particular trio is the Nordic UART set — a convention so common that serial-over-BLE apps recognise it on sight.
Why you must subscribe
A notify characteristic only sends to phones that asked. Subscribing is how the phone says "keep me posted" — until then, the board's messages have nowhere to go.
05 Know it worked
Test & debug
Success and recovery sit side by side, so you never have to go hunting when something looks off.
What you should see
Waiting a client connection to notify...hello from the phone
The waiting line prints once at start-up. After you connect and write from the phone, each message appears as its own line — a stray `Test` right after connecting is just the sketch's starter value.
If it doesn't
- ESP32S3_Bluetooth never appears in LightBlue? Power-cycle the board and swipe down to rescan — it starts advertising at boot. Look for it inside the app; BLE devices skip the phone's Settings→Bluetooth pairing list.
- Nothing arrives on the phone? Open the characteristic ending 0003 and tap Subscribe first — notifications only flow to subscribers.
- Garbled symbols on the phone? Set the characteristic's Data Format to utf-string.
- Nothing lands in Serial Monitor? Confirm 115200 baud, and that you're writing to the characteristic ending 0002.
- Can't reconnect after a disconnect? Press the board's reset button, then rescan — this sketch advertises once at boot, a known quirk.
06 Make the idea yours
Try this: name your boat, find the edge
Same working sketch, two experiments — one line of code, then a walk. It fits inside today's 25 minutes.
Fly your own name
Change setupBLE("ESP32S3_Bluetooth") to setupBLE("YourBoatName"), re-upload, and rescan in LightBlue — your board now broadcasts under its own flag.
Find the range edge
Stay subscribed on the phone and walk to the far end of your home while a helper (or a repeated send) keeps messages coming from Serial Monitor. Note where they stop arriving.
Logbook
07 Learn it with a hand on the tiller
Coach me through it
Every lesson ships with a code and a machine-readable packet, so an agent can guide you with full context.
Lesson code
TSK-DAY27-BLE
Context packet
How the agent should behave: work one end at a time — board side in Serial Monitor, phone side in LightBlue — confirm the waiting line before touching the app, and treat subscribe, data format, and reset-after-disconnect as the first checks.