The Software
The Arduino environment can be used to program ESP8266 WiFi boards. To configure the Arduino IDE v1.6.5
or newer, go to File -> Preferences and add the following Additional Boards Manager URL:
http://arduino.esp8266.com/stable/package_esp8266com_index.json
Then go to Tools -> Board -> Boards Manager. Install the latest esp8266 board manager.
Libraries
Available libraries include HTTP servers, mDNS / Bonjour & SSDP service discovery alongside
any other Arduino libraries which don’t make use of native ATMEL hardware functions.
An implicit ESP object provides access to platform native functionality not found in the other
Arduino environments.
The Hardware
The most common board is the ESP01. It’s a tiny 3.3v device with 2 rows of 4pin headers at one end and
a pcb antenna at the other. It’s capable of WiFi b/g/n in client or access point modes at up to 300m range.
The processor runs at 80MHz and has a 512K SPI flash alongside it which runs at 40MHz. 64K of this flash
is used as a filesystem (SPIFFS).
There are 4 GPIO pins, 2 of which double up as UART Tx/Rx. The UART defaults to 115200 baud rate. There’s
also a blue LED on the GPIO1 / UART TXD pin, it is active when the GPIO1 line is pulled low.
Pinouts
With the board sitting so that the PCB antenna is facing upwards on the right hand side, the pins are:
| GPIO1 / UART TXD / Blue LED | GND |
| Chip Enable (pullup to Vcc) | GPIO2 |
| RST | GPIO0 |
| Vcc | GPIO3 / UART RXD |
If using GPIO1 and / or GPIO3, then the Serial port is unavailable. Likewise, if using the serial port
then only 2 GPIOs are available for use.
The nature of the pinout means these boards are not particularly easy to use with a protoyping
breadboard. I went with this idea: http://tim.jagenberg.info/2014/11/08/diy-esp8266ex-breadboard-adapter/
Programming Connections
Whatever the pins are used for in your circuit, they are automatically overridden when the board is in
programming mode.
Connections to a 3.3v USB Serial adapter are:
| ESP8266 | Serial Adapter |
| GPIO1 / Tx | Rx |
| GND | GND |
| Chip Enable | 3.3v |
| GPIO2 | N/A |
| RST | RTS |
| GPIO0 | DTR |
| Vcc | 3.3v |
| GPIO3 / Rx | Tx |
Other Boards
Other boards are available, almost all of them expose more pins than the ESP01. The most flexible
appears to be the NodeMCU v1.0 which for around £5 comes with an ESP-12E, a much larger 4MB SPI flash,
an onboard voltage regulator and an onboard CP2012 USB to serial adapter all in a breadboard-friendly
sized package.