This ESP8266 breakout has a ton of pins available, compared to the mini ESP-01 module. When programming the breakout in Lua or via the Arduino IDE, you can control these I/O pins to light up LEDs, read buttons, talk to sensors etc. There's also a bunch of pins for power and control.
Power Pins
The ESP8266 requires 3.3V power voltage and peaks at 500mA or so of current for small periods of time. You'll want to assume the ESP8266 can draw up to 250mA so budget accordingly. To make it easier to power, we put a high-current-capable 3.3V voltage regulator on the board. It can take 3.4-6V in but you should stick to 4-6V since the ESP8266 has high current usage when WiFi is on.
There are two inputs for the regulator, V+ and VBat. Both have Schottky diodes so you can connect both at different voltages and the regulator will simply power from the higher voltage. The V+ pin is also on the FTDI/serial header at the bottom edge.
We recommend connecting your LiPoly or AA battery pack directly to VBat and then keeping V+ unused for when an FTDI cable is attached. You can also use the extra V+ pin for getting the 5V USB power from the FTDI connector for servos, NeoPixels, etc!
There's also a 3.3V output from the regulator available on the 3V pin
Serial pins
RX and TX are the serial control and bootloading pins, and are how you will spend most of your time communicating with the ESP module.
The TX pin is the output from the module and is 3.3V logic.
The RX pin is the input into the module and is 5V compliant (there is a level shifter on this pin)
The pins are available in two places, one set is on the right side breakout. The same pins are also at the bottom on the "FTDI/Serial" breakout
GPIO pins
This breakout has 9 GPIO: #0, #2, #4, #5, #12, #13, #14, #15, #16 all GPIO are 3.3V logic level in and out, and are not 5V compatible. Read the full spec sheet to learn more about the GPIO pin limits, but be aware the maximum current drawn per pin is 12mA.
These pins are general purpose and can be used for any sort of input or output. Most also have the ability to turn on an internal pullup. Many have special functionality:
GPIO #0, which does not have an internal pullup, and is also connected to both a mini tactile switch and red LED. This pin is used by the ESP8266 to determine when to boot into the bootloader. If the pin is held low during power-up it will start bootloading! That said, you can always use it as an output, and blink the red LED.
GPIO #2, is also used to detect boot-mode. It also is connected to the blue LED that is near the WiFi antenna. It has a pullup resistor connected to it, and you can use it as any output (like #0) and blink the blue LED.
GPIO #15, is also used to detect boot-mode. It has a pulldown resistor connected to it, make sure this pin isn't pulled high on startup. You can always just use it as an output
GPIO #16 can be used to wake up out of deep-sleep mode, you'll need to connect it to the RESET pin
GPIO #4 and #5 are used for I2C SDA and SCL (respectively) by default on Arduino IDE. We recommend that if you are using Arduino, connect your I2C devices there!
Rev A of this board had GPIO #4 and #5 swapped (the modules changed pinouts on us) so if #4/#5 aren't working for you, try swapping!
Analog Pins
There is also a single analog input pin called A. This pin has a ~1.0V maximum voltage, so if you have an analog voltage you want to read that is higher, it will have to be divided down to 0 - 1.0V range
Other control pins
We have a few other pins for controlling the ESP8266
- LDO - this is the enable pin for the regulator. By default it's pulled high, when connected to ground it will turn off the 3.3V regulator and is an easy way to cut power off to the whole setup. There is a 10K pullup is to whatever has a higher voltage, V+ or VBat. (See the schematic if you're unclear)
- RST - this is the reset pin for the ESP8266, pulled high by default. When pulled down to ground momentarily it will reset the ESP8266 system. This pin is 5V compliant.
- EN (CH_PD) - This is the enable pin for the ESP8266, pulled high by default. When pulled down to ground momentarily it will reset the ESP8266 system. This pin is 3.3V logic only
