ESP8266

Notes on the ESP8266 chip.

Overview

This board enables Arduinos and other embedded devices to communicate with wireless networks via the 802.11 protocol.

The board has a microchip that implements the entire TCP/IP stack, so you don't have to implement it on your embedded device. The embedded device simply uses serial commands to control and interact with the chip. Think of it as a dumbed-down, physical API for wifi.

The chip has an 8-pin array on the underside. The pins here use 3.3 V logic, so it is important you use it with embedded devices that also use 3.3 V logic! Some embedded devices (such as the Arduino Uno) use 5 V logic. If you have a device using 5 V logic, you need a down-converter (also called a level shifter) to convert the 5 V logic signals to 3.3 V logic signals.

Pinout

The 8 pins on the chip are arranged as follows:

___________________________________________
|        _______            _____________  |
|   (1)  | O O | (2)        |   _________| |
|        |     |            |   |________  |
|   (3)  | O O | (4)        |    ________| |
|        |     |            |   |________  |
|   (5)  | O O | (6)        |    ________| |
|        |     |            |   |________  |
|   (7)  | O O | (8)        |            | |
|        -------            |            | |
|__________________________________________|

(1) TXD     (2) GND
(3) CH_PD   (4) GPIO2
(5) RST     (6) GPIO0
(7) VCC     (8) RXD

Serial Communication

To communicate with the chip, use serial commands, at a baud rate of 57600.

Commands fall into three different categories:

• Set
  • Modify the parameters on the chip
• Inquiry
  • Read the current state of the chip's parameters
• Test
  • Return the different modes supported

The AT commands are all listed in the following table: http://wiki.iteadstudio.com/ESP8266_Serial_WIFI_Module#AT_Commands

Mini USB to Serial UART Board

I was using a PL2303 board, which has a Mini USB connector on one side and four serial pins on the other. Once nice aspect of this board is, you can control the voltage level with a jumper, so it can operate in 3.3 V or 5 V mode, depending on how you place the jumper.

Originally, I made the mistake of using an ArmorView USB to TTL 4-pin connector, which was a cheap knockoff of a USB-to-serial adapter from Prolific. I hooked it up to the board and tried to send a signal to it. However, the ESP8266 requires 3.3 V, so I fried the board. The board was only hooked up for about 5 seconds, but it still got cooked - it smelled like overheated electronics and was physically hot.

Using the PL2303 board solves that problem. It is relatively straightforward:

Wiring of PL2303 and ESP8266

To wire up the Mini USB to serial adapter,

Serial Software

To communicate with the serial device, I used Pyserial, which is a Python library for communicating with serial devices.

The program we will write will communicate with the wifi chip by sending various AT commands out over the transmit wire. There is a comprehensive list of all of the AT commands here: http://wiki.iteadstudio.com/ESP8266_Serial_WIFI_Module#AT_Commands

To test communication with the device, I started by sending a simple "AT" command. The ESP8266 should return an "OK" message.

Serial Experiments

Because this didn't work immediately, I had to try a couple of combinations of different parameters.

Variables:

• Baudrate - 57600 or 115200 (depending on chip/board version)
• RX/TX pinouts
• High/floating CH_PD pin

First round (slow rate, v 1):

Test 1A: 57600 baud rate, RX on ESP8266 connected to TX on PL2302 (mini usb to serial board), CH_PD pin floating

• Nope.

Test 2A: 57600 baud rate, RX on ESP8266 connected to TX on PL2302 (mini usb to serial board), CH_PD pin high

• Nope.

Test 3A: 57600 baud rate, RX on ESP8266 connected to RX on PL2302 (mini usb to serial board), CH_PD pin floating

• Nope.

Test 4A: 57600 baud rate, RX on ESP8266 connected to RX on PL2302 (mini usb to serial board), CH_PD pin high

• Nope.

Second round (fast rate, v 2):

Test 1B: 115200 baud rate, RX on ESP8266 connected to TX on PL2302 (mini usb to serial board), CH_PD pin floating

Test 2B: 115200 baud rate, RX on ESP8266 connected to TX on PL2302 (mini usb to serial board), CH_PD pin high

Test 3B: 115200 baud rate, RX on ESP8266 connected to RX on PL2302 (mini usb to serial board), CH_PD pin floating

Test 4B: 115200 baud rate, RX on ESP8266 connected to RX on PL2302 (mini usb to serial board), CH_PD pin high

Useful Links

Comprehensive Guide

There is a comprehensive guide to this chip here: http://wiki.iteadstudio.com/ESP8266_Serial_WIFI_Module

Github Pages

The ESP8266 has a wiki and a collection of related repositories on Github.

Link to wiki: https://github.com/esp8266/esp8266-wiki/wiki

Link to Github repos: https://github.com/esp8266