Such a chip is born in order to supply the WiFi connectivity to mobile or wearable devices that are battery powered, and thus implements low energy consumption modes; in fact the module may be operating in different modes: active mode, sleep mode and deep sleep mode, accordingly to the active peripherals.
In the sleep mode, the radio module is turned off while the real-time clock and the watchdog remain active, the absorption is only 12 µA; in this mode it is possible to program the internal timer so that it may activate the radio module at regular intervals in order to send or receive data. Even the external signals may activate the radio module and enable the transmissions. By means of the internal software it is also possible to reduce the emission power and to reduce the energy consumption in applications for which short range communications are required (such as wearable devices). The CHIP_PD line, that is available on the external connector, allows to bring the module to the low power state, with a power absorption close to zero.
The power absorption during the active mode reaches a maximum of 215 mA at the maximum transmission power, with a 802.11b protocol at 11 Mbps, dropping to 145 mA with a 802.11g protocol at 54 Mbps, and also only 60 mA for sending a 1.024 byte packet with an antenna power of -65dBm.
Inside the ESP8266 chip we find a 32 bit microcontroller, completed of ROM, RAM and SRAM for the program and data; the chip has several digital I/O lines and analog inputs, in addition to different communication ports such as I²C, SPI and UART. The communication ports may act as slave, so to interface memories that are external to the module, and to expand their functioning. The available digital lines are sixteen, and configurable as inputs or outputs, all have a pull-up resistor and are configurable in order to generate an interrupt; some lines may be configured so to remotely activate different energy saving modes. Some analog input and output lines – based on a PWM sigma-delta converter – are available as well.
The chip has been designed in order to operate at a 3.3V voltage, with a tolerable maximum of 3.6V, the digital inputs have a dedicated circuit (overvoltage protection) so to protect the integrated circuit from input voltages above 6V.
Lastly, we mention the support for all the most modern encryption protocols:WEP (RC4), CCMP (CBC-MAC, counting mode), TKIP (MIC, RC4) o WAPI (SMS4), WEP (RC4), CRC, WPA, WPA2 and WPS.
An integrated circuit, many WiFi modules
On the market there are various versions of the WiFi module that are based on the ESP8266 chip, and that are differentiated as for size and pins made available on the communication connector, besides the different versions of the internal firmware.
ESP-01: the most common module, with an antenna that is integrated in the PCB
– 2×4 contacts pinout, 2,54 step;
– antenna on PCB;
– 2 GPIOs;
– UART URXD/UTXD;
– reset and CH_PD (Power Down) function;
– size: 14,2 x 14,2 mm.
ESP-02: module with a connector for an external antenna, that is compatible with a breadboard
– 2×4 contacts pinout, 2,54 DIP step;
– 2 GPIOs;
– UART URXD/UTXD;
– reset and CH_PD (Power Down) function;
– size: 14,7 mm x 14,2 mm.
ESP-03: SMT (Sufrace Mount Technology) version, with all the pins made available and a ceramic integrated antenna
– 2 rows of 7 contacts, 2,54 mm step;
– ceramic integrated antenna;
– 7 GPIOs;
– UART URXD/UTXD;
– reset and CH_PD (Power Down) function;
– size 12,2 mm x 17,4 mm.
ESP-04: SMT (Sufrace Mount Technology) version with all the pins made available but without antenna
– 2 rows of 7 contacts, 2,54 mm step;
– external antenna;
– 7 GPIOs;
– UART URXD/UTXD;
– reset and CH_PD (Power Down) function;
– size: 12 mm x 15 mm.
ESP-05: Version with UART communication only and antenna connector
– 2×4 contacts pinout, 2,54 mm step;
– U-FL connector for an external antenna;
– no GPIO;
– UART URXD/UTXD;
– reset and CH_PD (Power Down) function;
– size 14,2 x 14,2 mm.
In order to complete the ESP8266 chip’s description, we will refer the functioning of the single pins in Table.
Function of the pins in the ESP8266 chip.
In some modules, some LEDs are found: the red LED indicates that there is power voltage (POWER STATUS) while the blue LED flashes when the module starts the boot (MODULE STATUS) or communication operations.
ESP03 module’s pinout.
