The 5 pin version of the ESP8266 Esp-05 WiFi module has the following connections on the 5 pin header
Reset – active low reset (apply low voltage level to reset), EXT_RSTB pin 32 on ESP8266 chip
GND – GND or 0V of power supply
(Rx – UART receive pin (3.3V logic level
(Tx – UART transmit pin (3.3V logic level
Vcc – 3.3V power supply Vcc connection
There is an aerial or antennae connector at the top left of the board for an external aerial / antennae.
An additional GND connection can be found at the top right of the board.
The ESP8266 chip and ESP-05 module operate at a voltage of 3.3V (working range is 3.0V to 3.6V). I/O pins including the UART pins operate with 3.3V logic.
The chip and module I/O and UART pins are NOT 5V tolerant.
A operating current average value of 80mA is given for the EXP8266 chip in the datasheet.
The ESP8266 SDK getting started guide gives the following note for their evaluation board modules:
The ESP8266 Wi-Fi module needs 3.3V power supply and may draw current in the order of 500mA.
Note that this current value is for the Espressif modules and not the ESP-05, but it does give some idea of the current that some modules can draw. The following current consumption values are for the EXP8266 chip when transmitting and receiving. These are the highest typical values from the datasheet.
The datasheet for the ESP8266 shows a highest typical current consumption of 170mA under the following conditions: Tx802.11b, CCK 11Mbps, P OUT=+17dBm
The datasheet for the ESP8266 shows a highest typical current consumption of 56mA under the following conditions: Rx 802.11g, 1024 bytes packet length, -70dBm