ESP32-S3 board
The brain that runs your uploaded sketch — its Bluetooth radio is built in.
01 First, know the pieces
What you need
Six things, most of them old friends from your first circuits. Tap Define on any part you haven't met — the answer opens as a field note you can read and dismiss without losing your place.
GPIO extension board
Spreads the pins into rows you can reach and label.
LED
The light your phone will switch — it only works one way round.
220 Ω resistor
Sits in series with the LED to keep the current gentle.
2 jumper wires (M/M)
Two are enough today — the LED's feed and its return to ground.
Arduino IDE
Uploads the sketch and opens Serial Monitor.
02 Make the physical circuit
Chart the circuit
The official Freenove diagram is your chart — schematic on top, the same circuit built on a breadboard below. Click it to enlarge. The circuit is the one-LED layout you know from Blink; the command now arrives by radio.
LED long leg (+)
→GPIO 2 via 220 Ω
This pin obeys the command your phone sends.
LED short leg (−)
→GND
Completes the LED's path back to zero volts.
Mind the LED's legs. The LED only lights one way round — long leg toward GPIO 2 through the 220 Ω resistor, short leg to ground. Unplug USB before you move any wire.
03 One action at a time
Build it
This is the main path — you can finish the day without opening a single field note. Tap each step as you go to keep your place.
0 / 9 done
Seat the ESP32-S3 on the GPIO extension board and keep USB unplugged while you wire.
Place the LED so its long leg (+) is on the GPIO 2 side and its short leg (−) heads toward ground.
Put the 220 Ω resistor in series between GPIO 2 and the LED's long leg.
Compare every wire to the chart, then plug in USB.
Open
Sketch_20.2_BluetoothToLed.inoin Arduino IDE and upload it.Open Serial Monitor at
115200and look for the "device started" line.On your phone, open LightBlue and connect to
ESP32S3_Bluetooth, exactly as you did on Day 27.Find the write characteristic, set the format to utf-string, and write
led_on— underscore, exact spelling.Watch the LED light, then write
led_offto put it out.
04 Read just enough code
Read the code
The BLE plumbing at the top of this sketch is Day 27's, line for line — same service, same name. Today's new idea lives in loop, where the board compares whatever arrived against two known commands and acts. Switch to MicroPython if you'd rather see the same idea in Python — the wiring never changes.
#define LED 2
void setup() {
pinMode(LED, OUTPUT);
setupBLE("ESP32S3_Bluetooth");
Serial.begin(115200);
Serial.println("\nThe device started, now you can pair it with Bluetooth!");
}
void loop() {
long now = millis();
if (now - lastMsg > 100) {
if (deviceConnected && strlen(rxload) > 0) {
if (strncmp(rxload, "led_on", 6) == 0) {
digitalWrite(LED, HIGH);
}
if (strncmp(rxload, "led_off", 7) == 0) {
digitalWrite(LED, LOW);
}
Serial.println(rxload);
memset(rxload,0,sizeof(rxload));
}
lastMsg = now;
}
}setupBLE("ESP32S3_Bluetooth")The same radio setup as Day 27 — the board advertises under the same name, with the same service underneath. strncmp(rxload, "led_on", 6) == 0True when the first six characters the phone wrote spell led_on — underscore included. The buffer rxload holds whatever landed in the write characteristic. digitalWrite(LED, HIGH)The matched command drives GPIO 2 HIGH and the LED lights; led_off drives it LOW again. Serial.println(rxload)Echoes every received command to Serial Monitor, so you can watch the words arrive as the LED obeys. Optional side path · same circuit
led=Pin(2,Pin.OUT)
def on_rx(rx_data):
print("Received: ", rx_data)
if rx_data == b'led_on':
led.value(1)
elif rx_data == b'led_off':
led.value(0)rx_data == b'led_on'Compares the received bytes to the exact command — every character must match, where the Arduino sketch checks only the front of the buffer.led.value(1)Drives GPIO 2 HIGH and the LED lights.Same pin, same wiring. Copy ble_advertising.py onto the board alongside this file. The Python version broadcasts as ESP32S3, so look for that name in LightBlue. Run it in Thonny if MicroPython is set up; otherwise skip it — it should never block the Arduino-first path.
05 Understand, don't memorise
The shape of a command
Day 27 gave you a pipe between phone and board. Day 4 gave you digitalWrite. Put them together and you have remote control — and the pattern in today's loop is the skeleton of every protocol you'll ever meet.
Phone writes
LightBlue writes your text into the board's write characteristic.
Buffer fills
The sketch copies the incoming bytes into rxload.
Two known words
strncmp checks the buffer against led_on and led_off.
Pin moves
digitalWrite drives GPIO 2 HIGH or LOW and the LED follows.
The model
phone text → match a known command → digitalWrite
Why spelling is the whole protocol
The board compares raw characters. led_on with an underscore is a command; anything else is just text that scrolls past, and the LED holds its state.
What the radio adds
BLE only carries the bytes. The meaning — which words count as commands and what they do — lives entirely in the sketch you wrote.
06 Know it worked
Test & debug
The proof is the LED obeying your phone — Serial Monitor backs it up by echoing each command as it lands.
What you should see
- Write led_on in LightBlue (utf-string format) — the LED lights.
- Write led_off — the LED goes dark.
- Any other text leaves the LED exactly as it was — the sketch only acts on its two known commands.
Serial Monitor at 115200 shows "The device started, now you can pair it with Bluetooth!" on boot, then echoes every command the board receives.
If it doesn't
- LED never reacts? Send the underscore spelling led_on exactly, in utf-string format.
- LED wired but dead? Long leg to GPIO 2 through the 220 Ω resistor, short leg to GND.
- Can't find the board? Repeat Day 27's LightBlue steps, and press reset before reconnecting.
- Monitor blank? Set the baud rate to 115200.
07 Make the idea yours
Try this: grow the protocol
Same working circuit, one new power: you decide what the commands are. It fits inside today's 25 minutes.
Add led_blink
Add a third strncmp branch for led_blink that flashes the LED twice — HIGH, a short delay, LOW, and again. Upload and send your new word.
Rename the commands
Change led_on and led_off to words of your own — keep the character counts in each strncmp honest — and drive the light with your own vocabulary.
Logbook
08 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-DAY28-BTLED
Context packet
How the agent should behave: guide one physical step at a time, wait for you to confirm, explain terms on request, and always check wiring, board, port, and USB before changing code.