Docs  /  Boards

UNO R3 WiFi (ATmega328P + ESP8266): specs and pinout

A third-party Uno-style board that carries an ATmega328P and an ESP8266 Wi-Fi chip with 4 MB flash on one board, with a CH340G USB-serial chip.

Buy on Compoden

Specs

Power

Pinout

This is a third-party board with no maker document. The table below is the standard Arduino UNO R3 header layout from the official UNO R3 manual (A000066), a different board; it is not confirmed for this one, so check your board's silkscreen. The DIP-switch routing between the ATmega328P, ESP8266 and CH340G is not documented, and neither is the board logic level.

Build with it

Project ideas for the UNO R3 WiFi (ATmega328P + ESP8266). Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.

• A Wi-Fi weather logger with an UNO R3 WiFi board and a DHT22 sensor: The ATmega328P reads the DHT22 on a digital pin and sends data to the ESP8266 over the board's serial link, which must be switched to the ESP8266 by the DIP switches (check your board's markings).
• A water tank distance reader sent over Wi-Fi with an UNO R3 WiFi board and an HC-SR04 ultrasonic sensor: The HC-SR04 is a 5 V module, which suits the 5 V ATmega328P side; keep its echo line away from the ESP8266 pins, which are 3.3 V only. A learning project, not an overflow safety system.
• A Wi-Fi controlled low voltage lamp switch with an UNO R3 WiFi board and a 5 V relay module: The ATmega328P drives the relay module input and the ESP8266 receives the on/off command over Wi-Fi. Use it for a low-voltage lamp only; mains wiring needs a qualified person.
• A Wi-Fi doorbell notifier with an UNO R3 WiFi board and a tactile push button: The button to ground on a digital pin (internal pull-up) triggers a message sent through the ESP8266; no level shifting is needed for a plain switch.

Common mistakes

• ESP8266 pins are not 5 V tolerant (VIH max 3.6 V) while the ATmega328P can run at 5 V; check the board serial link between the two chips before assuming it is level-shifted (source: link, Table 5-1, p.24; link, p.2).
• At 3.3 V the ATmega328P speed grade is limited to 10 MHz; 16 MHz needs the 4.5 to 5.5 V range (source: link, Features, p.2).
• Do not draw more than 40 mA from one pin (source: link, 29.1 Absolute Maximum Ratings).

Not covered by the official source

• No maker document is available for this third-party board: the regulator, CH340G wiring, DIP switches, ESP8266 flash/serial link and logic level are not documented.
• Header rows are copied from the official Arduino UNO R3 manual on the assumption of the UNO layout; they are not confirmed by a document for this board.
• Board-level supply current is not available.
• ESP8266 flash size (4 MB) comes from the listing title only and is not verified.

Sources

• link (ATmega48A/PA/88A/PA/168A/PA/328/P Data Sheet DS40002061B, Microchip 2020)
• link (ESP8266EX Datasheet v7.1, Espressif)
• Arduino datasheet A000066 (Arduino UNO R3 user manual A000066; a different board, used only for the standard header layout)