35. Why ESP32: Architecture, Memory and When to Leave the Uno

Project: Board passport

Before Wi-Fi and sensors, know the board on your bench. A board passport prints model, flash size and free heap so you can confirm you flashed the right kit and that there is headroom for later wireless stacks.

Sketch 1 prints the passport once. Sketch 2 is the useful meter: refresh heap every 2 s with millis and label whether heap looks comfortable for upcoming Wi-Fi labs.

The IoT shift

Units A-F taught reliable local control on the Uno. Many modern projects also need Wi-Fi, Bluetooth, larger buffers or faster math. ESP32 extends those labs when connectivity, speed or memory become the limiting factor - it does not replace Uno foundations.

CPU: ATmega328P vs Xtensa / RISC-V

Classic Uno R3: 8-bit AVR ATmega328P at 16 MHz. Classic ESP32: Xtensa dual-core at much higher clocks. Newer members (C3, C5, C6, P4 and others) use RISC-V.

Sketches still look like setup/loop, but the SoC underneath includes radio (on most chips) and megabytes of Flash on the module.

Flash, SRAM and PSRAM

Flash stores the program. SRAM is working memory. Some modules add PSRAM for large buffers. Wi-Fi stacks need far more RAM than Blink - free heap is your health check.

When Uno is enough vs when ESP32 wins

Stay on Uno for local 5 V labs, shields and simple I/O. Move to ESP32 for Wi-Fi/BT, larger sketches or faster sampling - paying the cost of 3.3 V rules and different pin maps.

Board note for this unit

Default: Tools -> Board -> esp32 -> ESP32 Dev Module. Serial Monitor at 115200. Match C3/C6/P4 board entries to your silkscreen.

Wiring and safe build sequence

1. USB data cable from PC to ESP32 DevKit
2. Select ESP32 Dev Module (or matching board) and the correct port
3. No external parts required

What this sketch is for: Discovery: confirm model, flash size and free heap after upload so you know which kit you are holding.

void setup() {
  Serial.begin(115200);
  delay(500);
  Serial.println("ESP32 board passport");
  Serial.print("Model: ");
  Serial.println(ESP.getChipModel());
  Serial.print("Flash: ");
  Serial.print(ESP.getFlashChipSize() / (1024 * 1024));
  Serial.println(" MB");
  Serial.print("Free heap: ");
  Serial.print(ESP.getFreeHeap());
  Serial.println(" bytes");
}

void loop() {}

What this sketch is for: Useful meter for later labs: reprint free heap every 2 s with millis, and label whether heap looks comfortable for Wi-Fi work (teaching threshold).

unsigned long lastPrint = 0;
const unsigned long intervalMs = 2000;
const uint32_t wifiComfortHeap = 80000;

void printPassport() {
  uint32_t heap = ESP.getFreeHeap();
  Serial.print("Model ");
  Serial.print(ESP.getChipModel());
  Serial.print("  Flash ");
  Serial.print(ESP.getFlashChipSize() / (1024 * 1024));
  Serial.print(" MB  Heap ");
  Serial.print(heap);
  Serial.print(" bytes  ");
  Serial.println(heap >= wifiComfortHeap ? "[ok for Wi-Fi labs]" : "[low heap - watch allocations]");
}

void setup() {
  Serial.begin(115200);
  delay(500);
  Serial.println("Board passport meter");
  printPassport();
  lastPrint = millis();
}

void loop() {
  if (millis() - lastPrint >= intervalMs) {
    lastPrint = millis();
    printPassport();
  }
}