This ESP-201 board is recommended as its offer more pins over ESP-01 with a cheaper price than ESP-12. ESP-201 utilizes ESP8266EX chip by Espressif Systems. ESP8266EX has been designed for mobile, wearable electronics and Internet of Things applications with the aim of achieving the lowest power consumption with a combination of several proprietary techniques. The power saving architecture operates mainly in 3 modes: active mode, sleep mode and deep sleep mode. The major application of this ESP8266EX chip to IoT includes home appliances, home automation, smart lug and lights, mesh network, industrial wireless control, baby monitors, IP cameras, sensor networks, wearable electronics, WiFi location-aware devices, security ID tags and WiFi positioning system beacons.

 

There are up to 17 GPIO pins.  They can be assigned to various functions by the firmware. Each GPIO can be configured with internal pull-up (except XPD_DCDC, which is configured with internal pulldown), input available for sampling by a software register, input triggering an edge or level CPU interrupt, input triggering a level wakeup interrupt, open-drain or push-pull output driver, or output source from a software register, or a sigma-delta PWM DAC. These pins are multiplexed with other functions such as I2C, I2S, UART and PWM.