Fig. 04 · Robotics Lab · Wi-Fi and two cores: reflow it, fit the headers, upload over the UART port

Build an ESP32-S3-DevKitC-1

ESP32-S3-DevKitC-1

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Bench

No reading yet

5 V rail

No reading yet

Current draw

0 mA

Build and break

1BuildNext up
Strip to the bare PCB
Start from the bare black board: 25.4 x 62.7 mm, two copper layers, solder paste on every pad.
2
Pick and place the SMD parts
3
Reflow
4
Fit the pin headers
5
Solder the header pins
6
Plug USB into the UART port
7
Upload the colour wheel
8
Break it: leave out R17Break it
9
Break it: a cold joint on the UART portBreak it
10
Break it: reverse polarity on the 5V pinBreak it
11
Break it: 5 V on the 3V3 pinBreak it
12
Upload the Wi-Fi web server
13
Break it: brown-out on a weak USB portBreak it
14
Upload deep sleep
15
Break it: GPIO0 held low at resetBreak it
16
Force download mode by hand
17
Exploded view

Break it on purpose

Each fault is one that catches real builders. Trigger it, read the symptom on the bench, then fix it.

R17 left out: RGB LED dark
missing part
Why it happens
Symptom: The red power LED is on and the serial monitor prints the hue every second, but the RGB LED never lights.
R17 is a 0 Ω link that carries GPIO38's data signal to the LED's DIN pin. Without it the LED gets power but no data, so it stays dark however correct the code is.
Fix: Unplug, solder R17 back on with hot air, plug back in.
Cold joint on the UART port
cold solder joint
Why it happens
Symptom: The board reboots at random, the ROM banner repeats in the serial monitor and the computer keeps dropping the port.
A cold joint on the Micro-USB socket makes contact only some of the time, so VBUS or a data line comes and goes. Every dropout restarts the chip.
Fix: Unplug, reflow the joint until the solder flows and wets the pad, plug back in.
Reverse polarity on the 5V pin
reverse polarity
Why it happens
Symptom: Nothing lights, the bench supply goes into current limit and the regulator U2 gets hot.
The 5V header pin is wired after the two Schottky diodes, so it has no reverse protection. A swapped supply drives the SGM2212's input below ground and current flows backwards through the regulator until it fails.
Fix: Unplug, swap the leads (red to 5V, black to G), replace U2 if it is damaged, power it up again.
5 V on the 3V3 pin
wrong voltage
Why it happens
Symptom: No LEDs, the module gets hot fast and the board is dead afterwards.
The 3V3 pins feed the ESP32-S3 module directly. Its absolute maximum supply is 3.6 V, so 5 V destroys it, and it back-feeds the bridge and LEDs through R24.
Fix: Unplug. Feed 5 V only to the 5V pin or a USB port and let the regulator make 3.3 V. Replace the module.
Brown-out during Wi-Fi
brown-out
Why it happens
Symptom: "Brownout detector was triggered" in the serial monitor, the ROM banner again, the board never stays connected.
Wi-Fi transmit bursts draw up to about 355 mA. Through a weak USB port, a long thin cable or an unpowered hub the 5 V input sags, the regulator drops out and the 3.3 V rail dips below the brown-out threshold, so the chip resets.
Fix: Use a short, thick cable on a powered port or a 5 V supply that gives at least 500 mA; keep a 10 µF capacitor close to the module.
GPIO0 held low at reset
strapping pin
Why it happens
Symptom: The serial monitor shows "boot:0x0 (DOWNLOAD(USB/UART0))" and "waiting for download"; the sketch never starts.
GPIO0 is a strapping pin. The chip reads it at reset: high boots from flash, low enters the ROM download mode. Anything that holds it low at that moment keeps your program from starting.
Fix: Move the button or sensor to a free GPIO such as GPIO4, or make sure it leaves GPIO0 high at reset, then press RESET.

Meet the bench

Build it, plug the UART port in, upload, then open the web page from a phone on the same Wi-Fi

The ESP32-S3 is the step up from an Uno when a robot needs Wi-Fi, Bluetooth LE, more speed or two cores, and the DevKitC-1 costs less than an Uno. The board adds what the bare module lacks: a 3.3 V regulator, a CP2102N USB-to-UART bridge with automatic download mode, BOOT and RESET buttons and an addressable RGB LED on GPIO38 (this is v1.1; v1.0 used GPIO48). Everything runs at 3.3 V: never put 5 V on a GPIO or on the 3V3 pin. Use the Arduino core to get things working fast, ESP-IDF when you need control over the cores and power, and MicroPython for quick sensor tests, never for a balancing loop.

Sources

On the bench

Selected

Sketch uses 289,680 bytes of program storage

Code: Blink RGB

// Blink the on-board RGB LED red once a second and count the blinks
const uint8_t RGB_PIN = 38;   // v1.1 board: the RGB LED's data line is GPIO38 (v1.0: GPIO48)
uint32_t count = 0;

void setup() {
  Serial.begin(115200);
}

void loop() {
  rgbLedWrite(RGB_PIN, 64, 0, 0);   // red at 64 of 255: bright enough at arm's length
  Serial.printf("blink #%lu\n", (unsigned long)count);
  count++;
  delay(500);
  rgbLedWrite(RGB_PIN, 0, 0, 0);    // all three colours off
  delay(500);
}

Practice tasks

0/4 tasks

Write the code, then run the checks. The run uses a virtual clock and a scripted world, so the same code always gives the same result.

Light the RGB LED on a v1.1 board

Arduino C++

This sketch was written for a v1.0 board and lights nothing on yours. Blink the RGB LED green twice a second on the right pin, and print green and off on each change.

Checks

Not run yetRuns for 3 s without an error
Not run yetDrives GPIO38 with rgbLedWrite, not RGB_BUILTIN
Not run yetPrints green at least three times in 3 s
Not run yetPrints off at least three times in 3 s

Hints

Arduino's generic ESP32-S3 Dev Module puts RGB_BUILTIN on GPIO48, the v1.0 pin. Look at the silkscreen next to the LED: RGB@IO38.
Name the pin yourself: const uint8_t RGB_PIN = 38; then rgbLedWrite(RGB_PIN, 0, 64, 0).

Code for Light the RGB LED on a v1.1 board

Switch the LED from your phone

Arduino C++

Extend the web server: /on lights the RGB LED green, /off switches it off and /data answers with live readings (Wi-Fi signal strength and uptime) as JSON. Print one line per request.

Checks

Not run yetJoins bench-lab and prints its IP address within 3 s
Not run yetGET /on switches the LED on
Not run yetGET /data reports the signal strength and the uptime
Not run yetGET /off switches the LED off
Not run yetHas handlers for /on, /off and /data

Hints

One handler per page: server.on("/on", handleOn); each handler ends with server.send(200, type, body).
WiFi.RSSI() gives the signal strength in dBm, millis() / 1000 the uptime in seconds.
Print exactly GET /on -> LED on, GET /off -> LED off and GET /data -> rssi <n> dBm, up <s> s.

Code for Switch the LED from your phone

Count the wake-ups

Arduino C++

Each wake prints boot #1 again because the counter lives in normal RAM, which deep sleep wipes. Keep the count across sleeps, make sure each line reaches the serial monitor, and sleep 5 s at a time with the LED dark.

Checks

Not run yetPrints boot #1 at the first start
Not run yetPrints boot #2 after the first sleep
Not run yetPrints boot #3 after the second sleep
Not run yetUses RTC_DATA_ATTR, Serial.flush() and esp_deep_sleep_start()

Hints

RTC_DATA_ATTR puts a variable in RTC memory, which stays powered in deep sleep.
Serial.flush() waits until the line has left the UART; switch the LED off before esp_deep_sleep_start().

Code for Count the wake-ups

Reaction timer on the BOOT button

Arduino C++

After a random 1 to 3 s the RGB LED turns green; press BOOT as fast as you can and print reaction <n> ms. Use an interrupt for the button, debounce it, time with millis() and never call delay().

Checks

Not run yetPrints a reaction time for the first press
Not run yetPrints one reaction time per press, bounces ignored
Not run yetUses an interrupt and millis(), and no delay()

Hints

BOOT is GPIO0 and reads LOW while pressed: attachInterrupt(digitalPinToInterrupt(0), onPress, FALLING).
Keep the interrupt short: store millis() and set a flag; ignore edges less than 50 ms after the last one.
random(1000, 3000) picks the wait; compare millis() - roundStart against it in loop() instead of waiting.

Code for Reaction timer on the BOOT button

Build and break

1BuildNext up

Strip to the bare PCB

Start from the bare black board: 25.4 x 62.7 mm, two copper layers, solder paste on every pad.

Pick and place the SMD parts

Reflow

Fit the pin headers

Solder the header pins

Plug USB into the UART port

Upload the colour wheel

Break it: leave out R17Break it

Break it: a cold joint on the UART portBreak it

Break it: reverse polarity on the 5V pinBreak it

Break it: 5 V on the 3V3 pinBreak it

Upload the Wi-Fi web server

Break it: brown-out on a weak USB portBreak it

Upload deep sleep

Break it: GPIO0 held low at resetBreak it

Force download mode by hand

Exploded view

On the bench

Selected

Sketch uses 289,680 bytes of program storage

Code: Blink RGB

// Blink the on-board RGB LED red once a second and count the blinks
const uint8_t RGB_PIN = 38;   // v1.1 board: the RGB LED's data line is GPIO38 (v1.0: GPIO48)
uint32_t count = 0;

void setup() {
  Serial.begin(115200);
}

void loop() {
  rgbLedWrite(RGB_PIN, 64, 0, 0);   // red at 64 of 255: bright enough at arm's length
  Serial.printf("blink #%lu\n", (unsigned long)count);
  count++;
  delay(500);
  rgbLedWrite(RGB_PIN, 0, 0, 0);    // all three colours off
  delay(500);
}

Build an ESP32-S3-DevKitC-1

The bench

Build and break

Strip to the bare PCB

Pick and place the SMD parts

Reflow

Fit the pin headers

Solder the header pins

Plug USB into the UART port

Upload the colour wheel

Break it: leave out R17Break it

Break it: a cold joint on the UART portBreak it

Break it: reverse polarity on the 5V pinBreak it

Break it: 5 V on the 3V3 pinBreak it

Upload the Wi-Fi web server

Break it: brown-out on a weak USB portBreak it

Upload deep sleep

Break it: GPIO0 held low at resetBreak it

Force download mode by hand

Exploded view

Break it on purpose

R17 left out: RGB LED dark

Cold joint on the UART port

Reverse polarity on the 5V pin

5 V on the 3V3 pin

Brown-out during Wi-Fi

GPIO0 held low at reset

Live status

Current draw

Check yourself

After: Reflow

After: Solder the header pins

After: Upload the colour wheel

After: Upload the Wi-Fi web server

After: Upload deep sleep

End of bench quiz

Meet the bench

Sources

On the bench

Practice tasks

Light the RGB LED on a v1.1 board

Checks

Switch the LED from your phone

Checks

Count the wake-ups

Checks

Reaction timer on the BOOT button

Checks

Build an ESP32-S3-DevKitC-1

The bench

Build and break

Strip to the bare PCB

Pick and place the SMD parts

Reflow

Fit the pin headers

Solder the header pins

Plug USB into the UART port

Upload the colour wheel

Break it: leave out R17Break it

Break it: a cold joint on the UART portBreak it

Break it: reverse polarity on the 5V pinBreak it

Break it: 5 V on the 3V3 pinBreak it

Upload the Wi-Fi web server

Break it: brown-out on a weak USB portBreak it

Upload deep sleep

Break it: GPIO0 held low at resetBreak it

Force download mode by hand

Exploded view

Break it on purpose

R17 left out: RGB LED dark

Cold joint on the UART port

Reverse polarity on the 5V pin

5 V on the 3V3 pin

Brown-out during Wi-Fi

GPIO0 held low at reset

Live status

Current draw

Check yourself

After: Reflow

After: Solder the header pins