Wi-Fi
Interfacing ESP 01 Wi-Fi with ESP32
What is the ESP 01?
A bare-bones ESP8266 Wi-Fi module controllable via AT commands, a cheap way to bolt Wi-Fi connectivity onto non-networked microcontrollers. The ESP-01 exposes just enough pins — power, UART, and two GPIO — to run the module in its simplest mode: forward AT commands over serial from an existing microcontroller like an Arduino Uno, and let the ESP-01 handle all the Wi-Fi networking, making it a low-cost bridge for otherwise offline projects that just need occasional connectivity (sending sensor data to the cloud, receiving simple remote commands).
Specifications
| Wi-Fi chipset | ESP8266 SoC, 802.11 b/g/n 2.4GHz Wi-Fi |
| Operating voltage | 3.3V DC only (NOT 5V tolerant on any pin) |
| Operating current | ~80 mA average, spikes to 200-300 mA during Wi-Fi transmit bursts |
| Flash memory | Typically 1MB onboard SPI flash on standard ESP-01 boards (ESP-01S variants may have more) |
| GPIO | Only 2 usable GPIO pins broken out (GPIO0, GPIO2) — the most limiting factor of this module |
| Programming interface | UART (TX/RX), controlled via AT command firmware by default, or reflashed with custom Arduino-core firmware |
| Form factor | Very small 8-pin module, the smallest and cheapest of the common ESP8266 breakout family |
ESP 01 Pinout
| Pin | Name | Description |
|---|---|---|
| 1 | VCC | Power, 3.3V DC only — do not supply 5V |
| 2 | GND | Ground |
| 3 | TX | UART transmit — connect to microcontroller RX |
| 4 | RX | UART receive — connect to microcontroller TX (3.3V logic, level-shift from 5V boards) |
| 5 | GPIO0 | General I/O; must be pulled LOW at boot to enter flashing mode, HIGH for normal AT-command run mode |
| 6 | GPIO2 | General I/O; must be pulled HIGH at boot for normal operation |
| 7 | CH_PD / EN | Chip enable — must be pulled HIGH for the module to run |
| 8 | RST | Active-LOW reset pin |
All ESP-01 pins are strictly 3.3V — connecting directly to a 5V Arduino's logic pins without a level shifter or resistor divider will damage the chip. The module also draws current spikes during Wi-Fi transmission that a microcontroller's onboard 3.3V regulator often can't supply reliably, so a separate 3.3V regulator capable of a few hundred mA is strongly recommended rather than powering it from an Arduino's 3.3V pin.
Setting Up ESP 01 with ESP32
Library
ESP8266WiFi by ESP8266 Community
Bundled with the ESP8266 Arduino core
Wiring
| Component pin | ESP32 pin | Note |
|---|---|---|
| VCC | 3.3V | ESP-01 needs a stable 3.3V supply capable of ~300mA peaks during Wi-Fi TX -- use a dedicated regulator if you see resets |
| GND | GND | — |
| TX | GPIO16 (RX2) | ESP-01 TX is 3.3V logic -- safe to connect directly |
| RX | GPIO17 (TX2) | — |
| CH_PD / EN | 3.3V | Must be pulled HIGH for the module to run |
| GPIO2 | 3.3V | Must be pulled HIGH at boot for normal operation |
| GPIO0 | Floating or pulled HIGH | Pull LOW only when re-flashing firmware; HIGH for normal AT-command operation |
Example code
This bridges the ESP32's UART2 to the ESP-01 running its stock AT-command firmware. Since the ESP32 already has its own Wi-Fi radio, pairing it with an ESP-01 is mainly useful for learning AT commands -- for new projects, using the ESP32's built-in WiFi library directly is simpler.
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