DIY ESP 12 Programmer | ESP8266 Programmer
How to make an esp 12f/12 or esp8266 programmer. ESP-01 is a low-cost esp8266 module, with built-in WIFI.

It was created as an Arduino WIFI module, but It's more powerful than an Arduino, than now if you must do a little module to control a relay or some simple digital datalogger It's the best solution.
Exists some variant of this module, but all have a processor L106 32-bit RISC microprocessor core based on the Tensilica Xtensa Diamond Standard 106Micro running at 80 MHz, when you buy one of It you must pay attention only to Flash, some have 512 KiB Flash, other 1MiB

Pin Definition

VCC: Power 3.0 ~ 3.6V
GND: Ground
RESET: External reset signal (Low voltage level: Active)
CH_PD: Chip Enable. High: On, the chip works properly; Low: Off, a small current
GPIO0: (FLASH) I/O General purpose IO, If low while reset/power on takes chip into serial programming mode
GPIO1: (TX)I/O General purpose IO and Serial TXd
GPIO3: (RX)I/O General purpose IO and Serial RXd
GPIO2: I/O General purpose IO and Serial1 TXd