📖 What You'll Learn in This Tutorial:

✓ Understanding ESP32 pinout and capabilities
✓ Differences between ESP32 and ESP8266
✓ Wiring relays to ESP32 (safe GPIO selection)
✓ Connecting DHT22, DS18B20, and NTC sensors
✓ ESP32 power requirements and best practices

ESP32 Overview

The ESP32 is the powerful successor to the ESP8266. It adds Bluetooth, dual-core processing, more GPIO pins, and better analog-to-digital converters. It's the ideal choice for advanced IoT projects that need more processing power or Bluetooth connectivity.

📊 ESP32 vs ESP8266 Comparison:

Feature	ESP8266	ESP32
Processor	Single-core 80/160 MHz	Dual-core 240 MHz
RAM	80 KB	520 KB
Flash	4 MB	4-16 MB
GPIO Pins	16	34+
ADC Channels	1 (10-bit)	18 (12-bit)
Bluetooth	No	Yes (BLE + Classic)
Touch Sensors	No	Yes (10)
Price	$3-5	$8-12

ESP32 Board Variants

OceanRemote works with most ESP32 development boards:

ESP32 Dev Module (30-pin) - Most common. Fits breadboards.
ESP32 Dev Module (36-pin) - More GPIO pins exposed.
ESP32-WROOM-32 - Standard module with 4MB flash.
ESP32-WROVER - Includes 4MB PSRAM for larger applications.
NodeMCU-32S - NodeMCU-style ESP32 board.
LOLIN D32 - Compact ESP32 board.

💡 Recommendation:

For most users, get a standard ESP32 Dev Module (30-pin). It's widely available, well-documented, and fully compatible with OceanRemote.

ESP32 Pinout Diagram (30-pin version)

                    ESP32 Dev Module (30-pin) Pinout
            ┌─────────────────────────────────────────────────────────────┐
            │                                                             │
            │  EN    ────┐  ┌────  3.3V          USB ┌───┐              │
            │  VP    ────┤  ├────  EN                 │   │              │
            │  VN    ────┤  ├────  VP                 │USB│              │
            │  GPIO34───┤  ├────  VN                 │   │              │
            │  GPIO35───┤  ├────  GPIO34             └───┘              │
            │  GPIO32───┤  ├────  GPIO35                                 │
            │  GPIO33───┤  ├────  GPIO32                                 │
            │  GPIO25───┤  ├────  GPIO33                                 │
            │  GPIO26───┤  ├────  GPIO25                                 │
            │  GPIO27───┤  ├────  GPIO26                                 │
            │  GPIO14───┤  ├────  GPIO27                                 │
            │  GPIO12───┤  ├────  GND                                    │
            │  GND     ────┘  └────  GPIO13                              │
            │  GPIO13───┐  ┌────  GPIO12                                 │
            │  GPIO9 ────┤  ├────  GPIO14                                 │
            │  GPIO10────┤  ├────  GPIO27                                 │
            │  GPIO11────┤  ├────  GPIO26                                 │
            │  GPIO6 ────┤  ├────  GPIO25                                 │
            │  GPIO7 ────┤  ├────  GPIO33                                 │
            │  GPIO8 ────┘  └────  GPIO32                                 │
            │                                                             │
            │  GPIO5 ────┐  ┌────  GPIO18                                 │
            │  GPIO17────┤  ├────  GPIO19                                 │
            │  GPIO16────┤  ├────  GPIO21                                 │
            │  GPIO4 ────┤  ├────  GPIO22                                 │
            │  GPIO0 ────┤  ├────  GPIO23                                 │
            │  GPIO2 ────┘  └────  GPIO15                                 │
            └─────────────────────────────────────────────────────────────┘

Important ESP32 Pin Notes

}

Pins	Status	Notes
GPIO0, GPIO2, GPIO5, GPIO12, GPIO15	⚠️ Boot pins	Have pull-up/down at boot, use with caution
GPIO34, 35, 36, 39	📥 Input-only	Cannot be used as outputs (relays won't work)
GPIO6-11	🚫 Avoid	Connected to internal flash, do not use
GPIO16, 17	⚠️ Used for PSRAM	Avoid if PSRAM enabled, safe otherwise
GPIO1, 3 (TX/RX)	🔧 Serial	Used for USB communication, avoid using

⚠️ Critical ESP32 Pin Warnings:

GPIO0 - LOW at boot = flashing mode. Keep HIGH or floating.
GPIO2 - Affects boot if pulled LOW. Onboard LED may be connected.
GPIO12 - Affects flash voltage (3.3V vs 1.8V). Keep floating or high.
GPIO15 - Affects boot if pulled HIGH. Keep LOW or floating.
Input-only pins (34-39) - Cannot output signals. Do NOT connect relays here!

OceanRemote Default Pin Assignments for ESP32

OceanRemote firmware uses these safe GPIO pins for relays:

}

Relay	GPIO	Safe for Boot?	Notes
Relay 1	GPIO2	⚠️ Caution	Must be HIGH at boot (relay OFF)
Relay 2	GPIO4	✅ Safe	No boot constraints
Relay 3	GPIO5	⚠️ Caution	Has pull-up at boot, but safe if relay OFF
Relay 4	GPIO12	⚠️ Caution	Affects flash voltage if pulled LOW
Relay 5	GPIO13	✅ Safe	No boot constraints
Sensor (DHT/DS18B20)	GPIO15	⚠️ Caution	Has pull-down at boot, ensure sensor doesn't pull HIGH
NTC Thermistor	GPIO34	✅ Safe	Input-only pin (perfect for analog sensor)

💡 Better ESP32 Pin Choices (for custom firmware):

If you want to change the pin assignments, these are the safest GPIOs: GPIO4, GPIO13, GPIO14, GPIO18, GPIO19, GPIO21, GPIO22, GPIO23, GPIO25, GPIO26, GPIO27, GPIO32, GPIO33. Avoid GPIO0, GPIO2, GPIO5, GPIO12, GPIO15 for relays.

Wiring Relays to ESP32

Here's how to connect 5 relay channels to your ESP32:

}

Relay	ESP32 GPIO	Relay Module Connection
Relay 1	GPIO2	IN1 → GPIO2, VCC → 5V, GND → GND
Relay 2	GPIO4	IN2 → GPIO4, VCC → 5V, GND → GND
Relay 3	GPIO5	IN3 → GPIO5, VCC → 5V, GND → GND
Relay 4	GPIO12	IN4 → GPIO12, VCC → 5V, GND → GND
Relay 5	GPIO13	IN5 → GPIO13, VCC → 5V, GND → GND

Wiring Sensors to ESP32

DHT22 Temperature & Humidity Sensor

}

DHT22 Pin	Connect to ESP32
VCC	3.3V or 5V
DATA	GPIO15
GND	GND

DS18B20 Digital Temperature Sensor

}

DS18B20 Pin	Connect to ESP32
VDD	3.3V
DATA	GPIO15 + 4.7kΩ pull-up to 3.3V
GND	GND

⚠️ DS18B20 Pull-up Resistor Required!

A 4.7kΩ resistor must be connected between DATA (GPIO15) and 3.3V. Without it, readings will fail.

NTC 10kΩ Thermistor (Analog)

NTC Thermistor Voltage Divider (ESP32):
         
         3.3V
          │
          ▼
        ┌───┐
        │NTC│  ← 10kΩ NTC (resistance changes with temperature)
        └───┘
          │
          ├──────► GPIO34 (ADC1_CH6)  ← Voltage measured here (12-bit ADC)
          │
        ┌───┐
        │10k│  ← Fixed 10kΩ resistor (R_series)
        │Ω  │
        └───┘
          │
         GND

📊 ESP32 ADC Notes:

The ESP32 has 12-bit ADC (0-4095) which is much more precise than ESP8266's 10-bit (0-1023). Use GPIO34, GPIO35, GPIO36, or GPIO39 for analog inputs. GPIO36 and GPIO39 are recommended for better linearity.

Complete Wiring Diagram

                    COMPLETE ESP32 WIRING (30-pin)
            ┌─────────────────────────────────────────────────────────────┐
            │                                                             │
            │  ┌─────────┐      ┌─────────────────────────────────────┐  │
            │  │ ESP32   │      │       5-Channel Relay Module        │  │
            │  ├─────────┤      ├─────────────────────────────────────┤  │
            │  │   USB   │      │  IN1 │ GPIO2                        │  │
            │  │   5V    ├──────┤  IN2 │ GPIO4                        │  │
            │  │   GND   ├──────┤  IN3 │ GPIO5                        │  │
            │  │   3.3V  ├───┐  │  IN4 │ GPIO12                       │  │
            │  │   GPIO2 ├───┤  │  IN5 │ GPIO13                       │  │
            │  │   GPIO4 ├───┤  │  VCC │ 5V                           │  │
            │  │   GPIO5 ├───┤  │  GND │ GND                          │  │
            │  │   GPIO12├───┤  └─────────────────────────────────────┘  │
            │  │   GPIO13├───┘                                           │
            │  │   GPIO15├─────┐    ┌─────────────────────────────┐     │
            │  │   GPIO34├─────┤    │        DHT22 Sensor         │     │
            │  └─────────┘     │    ├─────────────────────────────┤     │
            │                  └────┤ DATA │ GPIO15               │     │
            │                       │ VCC  │ 3.3V                 │     │
            │                       │ GND  │ GND                  │     │
            │                       └─────────────────────────────┘     │
            │                                                           │
            │                  ┌─────────────────────────────┐         │
            │                  │     NTC Thermistor          │         │
            │                  │  (Between 3.3V and GPIO34)  │         │
            │                  │  + 10kΩ to GND              │         │
            │                  └─────────────────────────────┘         │
            └─────────────────────────────────────────────────────────────┘

ESP32 Power Requirements

USB Power (Recommended for Testing)

Use a quality USB cable (not charge-only)
5V, 500mA minimum (2A recommended with relays)
Phone charger works well
Computer USB port works (may be limited to 500mA)

External Power (For Permanent Installation)

Connect 5-12V DC to the VIN pin (has voltage regulator)
Or connect regulated 3.3V directly to 3.3V pin (advanced users)
ESP32 consumes ~240mA with WiFi active
Each active relay adds ~70mA
Use 5V 2A power supply for 5 relays + ESP32

⚠️ Power Warning:

Do NOT power relays from the ESP32's 3.3V pin! Relays need 5V. Use the 5V pin (from USB) or an external 5V power supply.

The ESP32's voltage regulator can provide up to 600mA. If you're powering many relays, use an external 5V supply.

ESP32 Special Features

Dual-Core Processing - OceanRemote runs WiFi on Core 0 and your application on Core 1.
Bluetooth - Future OceanRemote versions may support Bluetooth control.
Touch Sensors - GPIO0, 2, 4, 12, 13, 14, 15, 27, 32, 33 have touch sensing.
Hall Effect Sensor - Built-in magnetic field sensor on most ESP32 boards.
Deep Sleep - Can go into deep sleep (μA range) and wake on timer or external trigger.

💡 When to Choose ESP32:

Choose ESP32 for: Bluetooth projects, better ADC accuracy, more GPIO pins, dual-core performance
Choose ESP8266 for: Simpler projects, lower cost, smaller physical size
Choose Pico W for: Python programming, 12-bit ADC, official Raspberry Pi ecosystem

Troubleshooting ESP32

Device Won't Boot / Continuously Resets

Check GPIO0, GPIO2, GPIO5, GPIO12, GPIO15 - ensure they're not in wrong state at boot
Disconnect all sensors and relays, test with bare board first
Try a different USB cable (many are charge-only)
Check serial monitor for boot loop error messages

Upload Fails (Connecting... timeout)

Hold the BOOT button while uploading, release when you see "Connecting..."
Lower upload speed to 115200
Check port selection
Press EN/RST button after upload attempt

WiFi Connection Issues

Check antenna connection (some boards have external antenna)
Move ESP32 closer to router
Check for 2.4GHz interference (microwave, cordless phones)

Relays Not Responding

Verify relay VCC connected to 5V (not 3.3V)
Check relay logic (Positive vs Negative) in dashboard settings
Test GPIO pin with a simple blink sketch before connecting relay
Check that you're not using input-only pins (34-39) for relays

🔧 ESP32 Boot Mode Pins Summary: }

Pin	Normal Boot	Flash Mode
GPIO0	HIGH or floating	LOW
GPIO2	HIGH or floating	Don't care
GPIO5	HIGH or floating	Don't care
GPIO12	HIGH or floating (3.3V flash)	LOW (1.8V flash)
GPIO15	LOW	HIGH

Next Steps

Now that you understand ESP32 wiring, continue with:

Tutorial 13: Raspberry Pi Pico W Pinout and Wiring
Tutorial 16-20: Working with sensors (DHT22, DS18B20, NTC)
Return to Tutorial 02: Generate and flash your firmware!

🎯 You're Ready!

Your ESP32 is now properly wired. You can now generate firmware from the OceanRemote dashboard and flash your device!

Tutorial 12: ESP32 - Pinout and Wiring Guide