Playing With a ESP8266 WiFi Module

2015-03-26: I open-sourced EspWiFi, a Arduino driver for the ESP8266 WiFi Module.

Lately, I started to play with some Arduino-based technologies after having made my very own Arduino DIY at AcoLab, a hackerspace based in Clermont-Fd. My new world domination plan, named coffuino, is to put a coffee machine over the Internets. I will write more on this project in the coming weeks, but as you may imagine for now, this project requires an Internet connection, hence the aim of this article. Let me introduce the ESP8266 WiFi Module, courtesy of Paul.

This is a serial module with a built-in TCP/IP stack, so you can use it standalone but you will be likely limited. You need a FTDI to connect this module to your computer, and start communicating with it. FTDI is a common name for USB-to-TTL (or serial) converter, FTDI being the company making and selling these products.

Wiring

I got a ESP-01 version of this module, which has 8 pins: VCC, GND, CH_PD, TX, RX, RST, GPIO0, and GPIO1. Wiring the module is not complicated and should be the same for all versions of this module:

• VCC needs 3.3V
• CH_PD has to be pulled-up (meaning it has to be connected to 3.3V as well)
• GND is connected to FTDI’s GND pin
• RX is connected to FTDI’s TX pin, because you want to create a loop: RX -> TX => RX -> TX
• TX is connected to FTDI’s RX pin
• other pins are left floating

The important detail here is that this module needs 3.3V, not 5V which is what most FTDIs supply. Mine has a jumper to supply either 3.3V or 5V. In case yours only supplies 5V, you need a voltage devider. Talking about power, this module requires more than 200mA, so use a dedicated power supplier for it. This is really important because a lack of intensity causes various issues!

I read that CH_PD should be pulled-up with a resistor (from 3k to 10k Ohms), however it did not work for me, so I connected this pin to VCC.

Connecting the Module

Now you can plug your USB cable to your laptop and try to reach your module using screen or any tool that can talk to a serial interface:

screen /dev/tty.usbserial-A50285BI 9600

Depending on the firmware version, baud rate is different: 9600, 57600 or 115200. This is another thing that can cause communication issues. Try different baud rates, it will either work, display gibberish, or simply fail… 115200 seems to be the default value, however most FTDIs are not able to work well at such a rate.

Once you find a decent baud rate, you can send a first AT comand to the module. The following AT command asks the module whether it is up:

AT

It should respond with OK. The AT command set is quite large, I cover a few commands in this post but feel free to try them all. Before having dug more with these commands, I chose to flash the module first, and then set 57600 as baud rate. It allowed me to communicate with the module in a reliable manner.

Upgrading the Firmware

Look at the espressif/esp8266_at repository to find recent (official) firmwares. In order to flash the module, you have to pull-down GPIO0 by wiring its pin to GND, then run esptool:

./esptool.py -p /dev/tty.usbserial-A50285BI write_flash 0x0000 boot_v1.1.bin \
    0x01000 user1.bin 0x7C000 esp_init_data_default.bin 0x7E000 blank.bin

boot_v1.1.bin, esp_init_data_default.bin, and blank.bin don’t really change, however choose the right user1.bin (see newest/ folder for instance). Recent firmwares obviously support cloud updates, but I did not try yet.

In order to change the baud rate, you have to connect to your module, then send the AT+CIOBAUD command with a value (57600 in this case):

AT+CIOBAUD=57600

If you want to use the module in a standalone mode, you will probably be interested in nodemcu, a lua based interactive firmware for mcu like ESP8266. Now that the communication with the module is ok, let’s join an access point.

Joining an Access Point

I chose pyesp8266, a Python script to tell the module to connect to an Access Point and ensure everything works:

python esp8266test.py <serial_port> <ssid> <password>

A few hints in case something is wrong with your setup:

• Is the red LED on the module lit? If it is not, the board is not getting power
• When trying to issue commands, do you see the blue LED on the module blinking? If not, check the RX/TX connections. If the LED is constantly lit, then one of the connections is wrong - probably RX/TX or one of the other pins
• Are you seeing gibberish? You are probably doing well, but try a different baud rate. In one of the provided scripts, run the AT+CIOBAUD command first (you have to modify the script)
• The script gets stuck on the AT+CWJAP command? Increase the timeout in the script (default is: 5 seconds, mine works with 10)

Running a TCP Server

As I said previously, this module embeds a TCP/IP stack, so you can tell the module to open a socket and listen at a given port. This is doable by manually sending AT commands or by using the esp8266server.py script, bundled with the pyesp8266 tool:

The script runs a simple TCP server on port 80 by sending the following AT commands:

# allow multiple connections
AT+CIPMUX=1

# run a TCP server on port 80
AT+CIPSERVER=1,80

In case you did not notice, it also send the AT+CIFSR to retrieve the IP address. Browsing it will give you a message starting wit GOT IT!

Coffuino, You Said?

coffuino is the project I am working on during my spare time, and it needs an Internet connection. I used this WiFi module and implemented a library to manage it in C++, which should be opensourced soon. There are a few libraries for Arduino, but I did not find any simple library that worked with my setup (my Arduino only has one hardware serial for instance).

The picture below is the prototype of coffuino (PS: you will find more teasers on Twitter):

The Arduino is powered by a former Apple USB cable (\o/) whereas the WiFi module uses the 3.3V output of my FTDI. Note that I set the baud rate to 115200 in order to connect the module to my Arduino (which perfectly handles such a rate).

I will give more details on the software part in another article.

Links

Because it would not have been possible without these articles and useful resources, thanks!

• Getting started with the esp8266 and Arduino
• noob’s guide to ESP8266 with Arduino Mega 2560 or Uno
• ESP8266 Teensy Time
• ESP8266 WiFi module
• ESP8266 - Upgrading the Firmware
• ESP8266 Community Forum
• ESP8266 Electrodragon
• esp8266/esp8266-wiki - Toolchain @ GitHub
• ESP8266 WiFi Module Quick Start Guide
• ESP8266 Offical AT+ Command @ GitHub