ESP 8xxx Family

At the moment, the ESP 8xxx family includes the following chips:

ESP8266EX (figure 1),
ESP8285 (figure 2).

The ESP8285 module continues the ESP8266 line with 1 MB of built-in flash, higher integration, and reduced dimensions.

ESP 8266

ESP 8266 General Information

The ESP8266 is a low-cost system-on-chip (SoC) microcontroller with WiFi and full TCP/IP stack capability ^[1]. The main advantages of that family are:

Low power consumption,
Availability of WiFi and Bluetooth connections,
Wide availability of low-cost modules from various suppliers,
Wide availability in a variety of form factors, including SoC.

The low price and the fact that the module had very few external components, which suggested that it could eventually be very inexpensive in volume, attracted many users to explore it.

Esp8266 Architecture Overview

The main standard features of the ESP8266EX are:
Processor

Main processor: L106 32-bit RISC microprocessor core based on the Tensilica Xtensa Diamond Standard 106Micro running at 80 MHz. Both the CPU and flash clock speeds can be doubled by overclocking on some devices. CPU can be run at 160 MHz, and flash can be sped up from 40 MHz to 80 MHz. Success varies from chip to chip.

Memory

External QSPI flash: up to 16 MB is supported (512 kB to 4 MB typically included),
32 kB instruction RAM,
32 kB instruction cache RAM,
80 kB user data RAM,
16 kB ETS system data RAM.

Interfaces

IEEE 802.11 b/g/n WiFi ,
Integrated TR switch, balun, LNA, power amplifier and matching network WEP or WPA/WPA2 authentication, or open networks,
17 GPIO pins,
SPI,
I²C (software implementation),
I²S interfaces with DMA (sharing pins with GPIO),
UART on dedicated pins, plus a transmit-only UART can be enabled on GPIO2,
10-bit ADC (successive approximation ADC).

Figure 3 shows functional block diagram of ESP8266 chip ^[2].

Figure 3: ESP8266&ESP8285 functional block diagram

ESP8266 Modules

Many still popular ESP8266-based modules are on the market ^[3]. These modules combine the ESP8266EX microcontroller and additional components mounted on the PCB.

The most popular are these produced by AI-Thinker and remain the most widely available ^[4]:

ESP-01 (512 kB Flash),
ESP-01S (1 MB Flash),
ESP-12 (FCC and CE approved),
ESP-12E,
ESP-12F (4 MB Flash, FCC and CE approved).

Popular modules from other manufacturers:

Sparkfun ESP8266 Thing,
Wemos D1 mini, D1 mini Pro ^[5].

The Espressif company also produces ready-made modules using the aforementioned chip. This is the series of ESP8266-based modules made by Espressif (table 1).

Table 1: Espressif ESP8266 modules

Name	Active pins	LEDs	Antenna	Shielded	Dimensions (mm)	Notes
ESP-WROOM-02^[6]	18	No	PCB trace	Yes	18 × 20	FCC ID 2AC7Z-ESPWROOM02
ESP-WROOM-02D^[7]	18	No	PCB trace	Yes	18 × 20	FCC ID 2AC7Z-ESPWROOM02D. Revision of ESP-WROOM-02 is compatible with both 150-mil and 208-mil flash memory chips
ESP-WROOM-02U^[8]	18	No	U.FL socket	Yes	18 × 20	Differs from ESP-WROOM-02D in that includes an U.FL compatible antenna socket connector
ESP-WROOM-S2^[9]	20	No	PCB trace	Yes	16 × 23	FCC ID 2AC7Z-ESPWROOMS2

The most widely used chipset ESP-01 is presented in (figure 4) and its pinout on (figure 5).

Module ESP12F with pinout is presented on (figure 6) and its pinout on (figure 7).

Among the other modules, it is worth being interested in WEMOS modules ^[10] (figure 8, figure 9). The WEMOS company offers dedicated sensor modules and inputs/outputs compatible with the processor modules. They are called WEMOS shields (figure 10).