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There's something very nice about ESP32 Wroom modules: you can use fixtures to quickly debug things, remove a module, solder it and viola, you have something working.
Or a bad board. Mostly those options.

====== Introduction ======

I've been using a fixture by [[http://www.diymalls.com/|DIYMall]] for some time at this point. From my perspective, its main feature is the support for ESP32-S3-WROOM-1U and ESP32-S3-WROOM-1 ([[https://www.espressif.com/sites/default/files/documentation/esp32-s3-wroom-1_wroom-1u_datasheet_en.pdf|datasheet]]).

{{:tamiwiki:users:6r1d:signal-2025-10-18-123252_002.jpeg?400|}} {{:tamiwiki:users:6r1d:signal-2025-10-18-123334_002.jpeg?400|}}

It is very helpful as a fixture. It is not helpful whatsoever in terms of having a proper documentation. If you open the DIYMalls site, it shows 403 and doesn't give you anything.

So, the fixture is easy to buy on AliExpress, for example, [[https://aliexpress.com/item/1005008525778779.html|here]], it works without hassle, and it will also require you trace all pins unless you have a reference.

Thus, I've traced everything I found so you don't have to.

====== Pin assignments ======

^ ESP32-S3-Wroom contact pad ^ Datasheet reference ^ Arduino pin ^ Board pin ^
| 39                         | IO1                 | 1           | D36       |
| 38                         | IO2                 | 2           | D35       |
| 4                          | IO4                 | 4           | D1        |
| 5                          | IO5                 | 5           | D2        |
| 6                          | IO6                 | 6           | D3        |
| 7                          | IO7                 | 7           | D4        |
| 12                         | IO8                 | 8           | D9        |
| 17                         | IO9                 | 9           | D14       |
| 18                         | IO10                | 10          | D15       |
| 19                         | IO11                | 11          | D16       |
| 20                         | IO12                | 12          | D17       |
| 21                         | IO13                | 13          | D18       |
| 22                         | IO14                | 14          | D19       |
| 8                          | IO15                | 15          | D5        |
| 9                          | IO16                | 16          | D6        |
| 10                         | IO17                | 17          | D7        |
| 11                         | IO18                | 18          | D8        |
| 23                         | IO21                | 21          | D20       |
| 31                         | IO38                | 38          | D28       |
| 32                         | IO39                | 39          | D29       |
| 33                         | IO40                | 40          | D30       |
| 34                         | IO41                | 41          | D31       |
| 35                         | IO42                | 42          | D32       |
| 24                         | IO47                | 47          | D21       |
| 25                         | IO48                | 48          | D22       |
| 36                         | RXD0                | 36          | D33       |
| 37                         | TXD0                | 37          | D34       |

===== Notes =====

  * GPIO pin 48 is the onboard LED, usually blue.
  * Initially, I thought that onboard USB-UART is connected to something else than RXD0 / TXD0. It was not. It is the main UART.
 
====== Tracing code: Arduino ======

You may disagree with me and want to run a quick check. For your convenience, there's a code to do so. I didn't bother to write it manually, but I have tested it and it worked for me.

Flash from Arduino IDE. Use the ESP32 board package by Espressif, pick ESP32S3 Dev Module, pick 115200 baud in Serial Monitor.

<file cpp esp32_s3_pin_tracer.ino>
#include <Arduino.h>

// ====== CONFIG ======
// Blink timing (change at runtime with: delay <ms>)
static uint32_t BLINK_DELAY_MS = 100;

// Conservative "test-safe GPIO" set for ESP32-S3 modules.
// Excludes pins that commonly serve boot strapping, USB D-/D+, PSRAM/flash, UART0 console, or JTAG,
// which can interfere with programming, boot, or board-level functions during quick tests.
//
// Notes (summarized from the ESP32-S3 module/chip docs):
// - 0, 3, 45, 46 are strapping/boot-related or JTAG-related; driving them can change boot modes or disable debug.
// - 19, 20 are the on-chip USB D-/D+ differential pair; toggling them breaks USB comms.
// - 35, 36, 37 are wired to Octal PSRAM on some variants; not available as GPIO there.
// - 43 (U0TXD), 44 (U0RXD) are UART0 console pins used by Serial; poking them disrupts logs/flashing.
// - 47, 48 form a differential SPI clock pair; safe as GPIO but mind 1.8 V I/O level on some R16V variants.
const uint8_t TEST_SAFE_GPIO[] = {
  1, 2,                      // ADC/Touch-capable, OK for digital use
  4, 5, 6, 7,                // "
  8, 9, 10, 11, 12, 13, 14,  // "
  15, 16, 17, 18,            // "
  // 19,20 excluded (USB D-/D+)
  21,  // plain GPIO
  // 22..34 don't exist on S3 modules
  // 35,36,37 excluded (PSRAM on some variants)
  38, 39, 40, 41, 42,  // JTAG-capable if configured, but OK as GPIO when JTAG is not in use
  // 43,44 excluded (UART0 TX/RX used by Serial)
  47, 48  // differential clock pair; OK as GPIO (watch 1.8 V I/O on some R16V variants)
};
const size_t TEST_SAFE_GPIO_COUNT = sizeof(TEST_SAFE_GPIO) / sizeof(TEST_SAFE_GPIO[0]);

// ====== RUNTIME STATE ======
static int currentPin = -1;
static bool blinking = false;

// ====== HELPERS ======
bool isTestSafe(int gpio) {
  for (size_t i = 0; i < TEST_SAFE_GPIO_COUNT; ++i) {
    if ((int)TEST_SAFE_GPIO[i] == gpio) return true;
  }
  return false;
}

void printTestSafePins() {
  Serial.println(F("\nTest-safe GPIOs (ESP32-S3):"));
  for (size_t i = 0; i < TEST_SAFE_GPIO_COUNT; ++i) {
    Serial.print(F(i ? ", " : "  "));
    Serial.print(TEST_SAFE_GPIO[i]);
  }
  Serial.println();
  Serial.println(F("Excluded (reason): 0,3,45,46 (boot/strap/JTAG) | 19,20 (USB D-/D+) | 35-37 (PSRAM on some) | 43,44 (UART0 console)"));
}

void stopBlink() {
  if (currentPin >= 0) {
    digitalWrite(currentPin, LOW);
    pinMode(currentPin, INPUT);  // leave safe
  }
  blinking = false;
  currentPin = -1;
  Serial.println(F("Stopped. Pin released to INPUT."));
}

void startBlink(int gpio) {
  if (!isTestSafe(gpio)) {
    Serial.print(F("Restricted: GPIO "));
    Serial.print(gpio);
    Serial.println(F(" is not in the test-safe set."));
    return;
  }
  if (blinking && currentPin == gpio) {
    Serial.print(F("Already blinking GPIO "));
    Serial.println(gpio);
    return;
  }
  // switch pin if needed
  if (blinking && currentPin != gpio) stopBlink();

  currentPin = gpio;
  pinMode(currentPin, OUTPUT);
  digitalWrite(currentPin, LOW);
  blinking = true;

  Serial.print(F("Blinking GPIO "));
  Serial.print(currentPin);
  Serial.print(F(" at "));
  Serial.print(BLINK_DELAY_MS);
  Serial.println(F(" ms."));
}

// Parse commands like:
//   list
//   pin 10
//   delay 250
//   stop
void handleCommand(String line) {
  line.trim();
  if (line.length() == 0) return;

  line.toLowerCase();
  if (line == "list") {
    printTestSafePins();
    return;
  }
  if (line == "stop") {
    stopBlink();
    return;
  }
  if (line.startsWith("pin ")) {
    int gpio = line.substring(4).toInt();
    startBlink(gpio);
    return;
  }
  if (line.startsWith("delay ")) {
    int v = line.substring(6).toInt();
    if (v < 10) v = 10;  // clamp a bit
    BLINK_DELAY_MS = (uint32_t)v;
    Serial.print(F("Set blink delay to "));
    Serial.print(BLINK_DELAY_MS);
    Serial.println(F(" ms."));
    return;
  }

  // Single-number shortcut: just type the GPIO number
  bool allDigits = true;
  for (size_t i = 0; i < (size_t)line.length(); ++i) {
    if (!isDigit(line[i])) {
      allDigits = false;
      break;
    }
  }
  if (allDigits) {
    startBlink(line.toInt());
    return;
  }

  Serial.println(F("Commands:"));
  Serial.println(F("  list               -> show test-safe GPIOs"));
  Serial.println(F("  pin <gpio>         -> start blinking that GPIO"));
  Serial.println(F("  <gpio>             -> same as 'pin <gpio>'"));
  Serial.println(F("  delay <ms>         -> set blink delay"));
  Serial.println(F("  stop               -> stop and release pin"));
}

void setup() {
  Serial.begin(115200);
  // give USB-Serial/JTAG a moment
  delay(400);
  Serial.println(F("\nESP32-S3 GPIO Quick Tester"));
  Serial.println(F("Type 'list' to see test-safe pins, 'pin <gpio>' to blink, 'delay <ms>' to change speed, 'stop' to release.\n"));
  printTestSafePins();
}

void loop() {
  // Process serial line input
  static String line;
  while (Serial.available()) {
    char c = (char)Serial.read();
    if (c == '\r') continue;
    if (c == '\n') {
      handleCommand(line);
      line = "";
    } else {
      line += c;
    }
  }

  // Blink the selected pin
  if (blinking && currentPin >= 0) {
    digitalWrite(currentPin, HIGH);
    delay(BLINK_DELAY_MS);
    digitalWrite(currentPin, LOW);
    delay(BLINK_DELAY_MS);
  } else {
    delay(5);
  }
}
</file>


====== Feedback ======


If you’d like to suggest corrections or aren’t satisfied with how I wrote this short article, feel free to ping me on [[https://t.me/I_am_6r1d|Telegram]].

This topic might deserve to be expanded into a document outside of my personal page.
Then again, I’m not sure how many people around here actually use ESP32-S3.
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