ESP32 Basics

The ESP32 is a low-cost microcontroller with integrated WiFi and Bluetooth, made by Espressif Systems. It's the heart of this telemetry project.

Key Specifications

Power Consumption

This is important for car applications where the ESP32 runs on OBD port power (12V stepped down).

Power Modes Explained

Active Mode: CPU running, radios active. Use this while driving.

Modem Sleep: WiFi maintains connection but radio sleeps between beacons. Good for reducing power while staying connected.

Light Sleep: CPU paused, RAM retained. Can wake on GPIO/timer. Good between transmissions.

Deep Sleep: Only RTC memory preserved (8KB). Everything else powered off. Wake on timer or external signal. Good when car is parked.

In Our Project

While driving: ~200mA at 3.3V = 0.66W Car OBD provides 12V, so with a buck converter: 0.66W / 12V = 55mA from car

This is negligible - car alternator produces 50-150A.

Dual-Core Architecture

ESP32 has two CPU cores:

• Core 0 (PRO_CPU): Usually handles WiFi/BLE stack
• Core 1 (APP_CPU): User application code

The Arduino framework runs your code on Core 1 by default. You can pin tasks to specific cores:

xTaskCreatePinnedToCore(
  taskFunction,  // Function
  "TaskName",    // Name
  10000,         // Stack size
  NULL,          // Parameters
  1,             // Priority
  NULL,          // Task handle
  0              // Core (0 or 1)
);

Memory Layout

┌─────────────────────────────┐
│        Flash (4MB)          │
│  ├── Bootloader             │
│  ├── Partition table        │
│  ├── Application (your code)│
│  └── SPIFFS/LittleFS (files)│
├─────────────────────────────┤
│         SRAM (520KB)        │
│  ├── .data (globals)        │
│  ├── .bss (zero-init)       │
│  ├── Heap (malloc)          │
│  └── Stack                  │
├─────────────────────────────┤
│      RTC Memory (8KB)       │
│  └── Survives deep sleep    │
└─────────────────────────────┘

BLE on ESP32

The ESP32's BLE stack is based on the Bluedroid stack (or NimBLE as alternative).

Key concepts:

• GATT: Generic Attribute Profile - how data is structured
• Service: A collection of characteristics (like a class)
• Characteristic: A data point (like a property)
• UUID: Unique identifier for services/characteristics

In our project, the ELM327 adapter exposes:

• Service UUID: 0000fff0-0000-1000-8000-00805f9b34fb
• TX Characteristic: 0000fff2-... (we write commands here)
• RX Characteristic: 0000fff1-... (we receive responses here)

WiFi on ESP32

#include <WiFi.h>

void setup() {
  WiFi.begin("SSID", "password");

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }

  Serial.println(WiFi.localIP());
}

The ESP32 supports:

• Station mode (connect to AP)
• Access Point mode (be an AP)
• Both simultaneously

Arduino vs ESP-IDF

We use Arduino framework for simplicity. ESP-IDF is Espressif's official SDK with FreeRTOS.

Common Pitfalls

1. Watchdog Timer: Long blocking operations trigger watchdog reset. Use yield() or delay(1) in loops.

2. Stack Overflow: Default task stack is small. Increase if using recursion or large local variables.

3. WiFi + BLE: Using both simultaneously increases power and memory. BLE stack alone uses ~70KB RAM.

4. String fragmentation: Using Arduino String class can fragment heap. Prefer char[] for embedded.

Resources

• ESP32 Datasheet
• ESP32 Technical Reference
• Arduino-ESP32 GitHub