ESP8266/ESP32

The ESP family are 32-bit MCUs that are produced by Espressif Systems, with integrated Wi-Fi (both) and Bluetooth (ESP32) functionality.

The ESP8266 first appeared in 2014, when it was sold by a third-party manufacturer, Ai-Thinker, in the form of a module (ESP-01) that could be used by another MCU or microprocessor-based systems to provide Wi-Fi functionality. The ESP-01 module contained firmware for this purpose, which allowed the module to be addressed using Hayes-style modem commands.

Its system specifications are as follows:

• Tensilica Xtensa Diamond Standard L106 microprocessor (32-bit)
• 80-160 MHz CPU speed
• Less than 50 KB of RAM available for user applications (with Wi-Fi stack loaded)
• External SPI ROM (512 KB to 16 MB)
• Wi-Fi support for 802.11 b/g/n

As the 32-bit MCU on the ESP-01 module was found to be capable of far more than the simple modem task assigned to it, it soon came to be used for more general-purpose tasks, with a range of upgraded ESP8266 modules (with integrated EEPROM chip), as well as breakout boards. Of the latter, the NodeMCU-style board has become very popular, though a number of other third-party manufacturers have made their own breakout boards, which provide different form factors and functionality.

The basic block diagram for the ESP8266EX looks as follows:

After the immense success of the ESP8266, Espressif Systems developed the ESP32, which used an upgraded, dual-core CPU, among other changes. Its block diagram looks like this:

Its specifications are as follows:

• Xtensa 32-bit LX6 (dual-core) microprocessor
• 160-240 MHz CPU speed
• 520 KB of SRAM
• Wi-Fi support for 802.11 b/g/n
• Bluetooth v4.2 and BLE (low energy)

Both the ESP8266 and ESP32 are generally sold as complete modules, with the MCU, external ROM module, and a Wi-Fi antenna either integrated into the board or with an external antenna option:

The metal shielding can covering the board helps to protect the board from electromagnetic interference,  benefiting its Wi-Fi (and Bluetooth, in the case of the ESP32) transceiver, but the whole design with a fixed antenna and geometry is required for FCC certification and later use as an approved module. Connecting an external antenna with higher gain may violate local regulations. The FCC ID it comes with is instrumental in getting a product containing such a module approved for commercialization.