ESP32 Introduction & Hardware Overview

What is ESP32?

ESP32 is a low-cost, low-power system-on-chip (SoC) microcontroller developed by Espressif Systems. It's the successor to the popular ESP8266 and has become the go-to choice for IoT projects, wearables, and connected devices.

Why ESP32 for Product Development?

ESP32 Family Overview

Espressif has released several variants. Understanding them helps you choose the right chip for your product.

ESP32 (Original)

The classic ESP32, still widely used.

Cores:          2x Xtensa LX6 @ 240MHz
SRAM:           520 KB
Flash:          External, typically 4MB
WiFi:           802.11 b/g/n (2.4GHz)
Bluetooth:      Classic + BLE 4.2
GPIO:           34 pins
ADC:            18 channels (12-bit)
DAC:            2 channels (8-bit)
Touch:          10 capacitive touch pins
Temperature:    -40°C to 85°C (industrial versions to 125°C)

Best for: General IoT, when you need both WiFi and Classic Bluetooth

ESP32-S2

Single-core, USB native, lower power.

Cores:          1x Xtensa LX7 @ 240MHz
SRAM:           320 KB
Flash:          External, typically 4MB
WiFi:           802.11 b/g/n (2.4GHz)
Bluetooth:      None
USB:            Native USB OTG
GPIO:           43 pins
ADC:            20 channels (13-bit)
DAC:            2 channels (8-bit)
Touch:          14 capacitive touch pins

Best for: USB devices, HID applications, lower power WiFi-only devices

ESP32-S3

Enhanced AI/ML capabilities, USB native.

Cores:          2x Xtensa LX7 @ 240MHz
SRAM:           512 KB + 8MB PSRAM option
Flash:          External, up to 16MB
WiFi:           802.11 b/g/n (2.4GHz)
Bluetooth:      BLE 5.0
USB:            Native USB OTG
GPIO:           45 pins
ADC:            20 channels (12-bit)
Vector Instructions: Yes (AI acceleration)

Best for: AI/ML edge computing, camera applications, USB devices with BLE

ESP32-C3

RISC-V architecture, cost-optimized.

Cores:          1x RISC-V @ 160MHz
SRAM:           400 KB
Flash:          External, typically 4MB
WiFi:           802.11 b/g/n (2.4GHz)
Bluetooth:      BLE 5.0
GPIO:           22 pins
ADC:            6 channels (12-bit)

Best for: Cost-sensitive WiFi/BLE products, simpler applications

ESP32-C6

WiFi 6 and Thread/Zigbee support.

Cores:          1x RISC-V @ 160MHz + 1x low-power RISC-V
SRAM:           512 KB
Flash:          External, typically 4MB
WiFi:           802.11 ax (WiFi 6, 2.4GHz)
Bluetooth:      BLE 5.0
802.15.4:       Thread, Zigbee, Matter
GPIO:           30 pins
ADC:            7 channels (12-bit)

Best for: Smart home (Matter), Thread/Zigbee mesh, WiFi 6 requirements

ESP32-H2

Thread/Zigbee focused, no WiFi.

Cores:          1x RISC-V @ 96MHz
SRAM:           320 KB
Flash:          External, typically 4MB
WiFi:           None
Bluetooth:      BLE 5.0
802.15.4:       Thread, Zigbee, Matter
GPIO:           26 pins

Best for: Battery-powered Thread/Zigbee devices, Matter accessories

Comparison Chart

*Relative pricing, actual costs vary by volume and distributor

Development Boards

When prototyping, you'll use a development board rather than the bare chip. Here are the main options:

Official Espressif Boards

ESP32-DevKitC

The standard reference board.

• Direct USB programming
• All GPIO pins exposed
• Built-in USB-to-UART bridge
• Breadboard-friendly (barely)
• Recommended for beginners

ESP32-DevKitM

Compact version with ESP32-MINI module.

• Smaller form factor
• Fewer exposed pins
• Good for space-constrained prototypes

Popular Third-Party Boards

NodeMCU-32S

• Similar to DevKitC
• Different pin layout
• Wide community support

WROOM vs WROVER Modules

WROOM: Standard module, external flash only

• ESP32-WROOM-32E (latest revision)
• Most common choice
• 4MB flash typical

WROVER: Includes PSRAM (extra RAM)

• ESP32-WROVER-E (latest revision)
• 8MB PSRAM
• Needed for: camera, audio buffers, large data

Specialized Boards

Choosing a Development Board

For Learning:

• ESP32-DevKitC v4 or NodeMCU-32S
• Widely documented, community support

For Product Prototyping:

• Choose based on your target chip (S3, C3, etc.)
• Consider form factor for enclosure design
• Check if you need PSRAM

For Quick Demos:

• M5Stack or TTGO with display
• Faster iteration, built-in UI

ESP32 Pinout Deep Dive

Understanding the pinout is critical for hardware design.

GPIO Overview (ESP32 Original)

Total GPIO:     34 pins
Input only:     GPIO 34, 35, 36, 39
Input/Output:   All others
Touch capable:  GPIO 0, 2, 4, 12, 13, 14, 15, 27, 32, 33
ADC1:           GPIO 32-39 (available with WiFi)
ADC2:           GPIO 0, 2, 4, 12-15, 25-27 (NOT available with WiFi!)
DAC:            GPIO 25, 26

Pin Categories

Boot Configuration Pins

These affect boot behavior, so be careful!

Strapping Pins Summary

GPIO 0:  LOW = Download mode, HIGH = Normal boot
GPIO 2:  Should be LOW or floating at boot
GPIO 5:  SDIO timing (usually fine to use)
GPIO 12: Flash voltage select (keep LOW for most boards)
GPIO 15: Silences boot messages if LOW

Safe GPIO for General Use

These pins have no boot restrictions:

GPIO 4, 13, 14, 16, 17, 18, 19, 21, 22, 23, 25, 26, 27, 32, 33

Input-Only Pins

GPIO 34, 35, 36, 39

• No internal pull-up/pull-down
• Often used for analog input
• Cannot drive outputs

ADC Considerations

ADC1 (Use with WiFi):

• Channels: GPIO 32, 33, 34, 35, 36, 39
• Always available

ADC2 (Conflicts with WiFi):

• Channels: GPIO 0, 2, 4, 12, 13, 14, 15, 25, 26, 27
• Cannot use while WiFi is active!
• Plan accordingly for IoT devices

ADC Characteristics:

• 12-bit resolution (0-4095)
• Non-linear response (needs calibration)
• Reference voltage ~1.1V (attenuated to 3.3V)
• Noisy, so average multiple readings

SPI Pins

ESP32 has multiple SPI interfaces:

VSPI (SPI3) - Default for user applications:
  MOSI: GPIO 23
  MISO: GPIO 19
  CLK:  GPIO 18
  CS:   GPIO 5 (or any GPIO)

HSPI (SPI2) - Alternative:
  MOSI: GPIO 13
  MISO: GPIO 12
  CLK:  GPIO 14
  CS:   GPIO 15

I2C Pins

Software-configurable (any GPIO), but defaults:

SDA: GPIO 21
SCL: GPIO 22

UART Pins

UART0 (Programming/Debug):
  TX: GPIO 1
  RX: GPIO 3

UART1 (User available):
  TX: GPIO 10 (default, often remapped)
  RX: GPIO 9 (default, often remapped)

UART2 (User available):
  TX: GPIO 17
  RX: GPIO 16

Complete Pinout Reference

                    ┌─────────────────┐
                    │    ESP32-WROOM  │
                    │                 │
           EN ──────┤ 1            38 ├────── GPIO 23 (VSPI MOSI)
   (Input) GPIO 36 ─┤ 2            37 ├────── GPIO 22 (I2C SCL)
   (Input) GPIO 39 ─┤ 3            36 ├────── GPIO 1  (TX0)
   (Input) GPIO 34 ─┤ 4            35 ├────── GPIO 3  (RX0)
   (Input) GPIO 35 ─┤ 5            34 ├────── GPIO 21 (I2C SDA)
   (Touch) GPIO 32 ─┤ 6            33 ├────── GND
   (Touch) GPIO 33 ─┤ 7            32 ├────── GPIO 19 (VSPI MISO)
   (DAC1)  GPIO 25 ─┤ 8            31 ├────── GPIO 18 (VSPI CLK)
   (DAC2)  GPIO 26 ─┤ 9            30 ├────── GPIO 5  (VSPI CS)
   (Touch) GPIO 27 ─┤ 10           29 ├────── GPIO 17 (TX2)
   (HSPI)  GPIO 14 ─┤ 11           28 ├────── GPIO 16 (RX2)
   (HSPI)  GPIO 12 ─┤ 12           27 ├────── GPIO 4  (Touch)
          GND ──────┤ 13           26 ├────── GPIO 0  (Boot)
   (HSPI)  GPIO 13 ─┤ 14           25 ├────── GPIO 2  (LED/Boot)
   (Flash) GPIO 9  ─┤ 15           24 ├────── GPIO 15 (HSPI CS)
   (Flash) GPIO 10 ─┤ 16           23 ├────── GPIO 8  (Flash)
   (Flash) GPIO 11 ─┤ 17           22 ├────── GPIO 7  (Flash)
          5V ───────┤ 18           21 ├────── GPIO 6  (Flash)
          GND ──────┤ 19           20 ├────── 3V3
                    └─────────────────┘

Note: GPIO 6-11 are used for flash - DO NOT USE

Electrical Specifications

Power Requirements

Operating Voltage:    3.0V - 3.6V (3.3V typical)
I/O Voltage:          3.3V (NOT 5V tolerant!)
Current (Active WiFi): 80-240mA
Current (Active BLE):  27-100mA
Current (Deep Sleep):  10µA
Current (Hibernation): 5µA

GPIO Electrical Characteristics

Output High (VOH):    ~3.3V (VDD)
Output Low (VOL):     ~0V
Max Output Current:   40mA per pin (20mA recommended)
Total GPIO Current:   1.2A max (all pins combined)
Input High (VIH):     >2.5V (0.75 × VDD)
Input Low (VIL):      <0.8V (0.25 × VDD)
Internal Pull-up:     ~45kΩ
Internal Pull-down:   ~45kΩ

Level Shifting for 5V Devices

ESP32 is 3.3V only! For 5V peripherals:

For Inputs (5V → 3.3V):

• Voltage divider (2:1 ratio)
• Level shifter IC (TXS0108E, 74LVC245)

For Outputs (3.3V → 5V):

• Level shifter IC
• Many 5V devices accept 3.3V logic

5V Input to ESP32 (Voltage Divider):

5V Signal ──┬── 10kΩ ──┬── ESP32 GPIO
            │          │
           GND        20kΩ
                       │
                      GND

Output: 5V × (20k/(10k+20k)) = 3.33V

Module Options for Production

When moving from development board to product, you'll use a module.

Popular Modules

Certification Advantage

Using pre-certified modules (like WROOM) means:

• No RF testing required for your product (intentional radiator)
• Faster time to market
• Lower certification costs
• Must follow module placement guidelines

Custom Design Considerations

If designing your own module (advanced):

• Full RF certification required
• Antenna design critical
• EMC compliance testing
• Higher NRE costs
• Only for very high volumes

Summary: Choosing Your ESP32

Decision Flowchart

Need Bluetooth Classic?
├── Yes → ESP32 (Original)
└── No
    └── Need WiFi?
        ├── No → ESP32-H2 (Thread/BLE only)
        └── Yes
            └── Need USB?
                ├── Yes
                │   └── Need BLE?
                │       ├── Yes → ESP32-S3
                │       └── No → ESP32-S2
                └── No
                    └── Need Thread/Matter?
                        ├── Yes → ESP32-C6
                        └── No
                            └── Cost priority?
                                ├── Yes → ESP32-C3
                                └── No → ESP32-S3

Quick Recommendations

Next: Development Environment Setup →