ESP8266 ESP-04 tips and tricks

ESP8266 ESP-04 moduleESP-04 module is one of the smallest ESP8266 boards. Its size is approximately 12.5x14.5mm i. e. smaller than 1 euro coin. It is Surface Mount Technology (SMT) module with 2mm pad spacing. The module has no on-board antenna. 
Seven GPIO pins are broken out: GPIO0, GPIO2, GPIO12, GPIO13, GPIO14, GPIO15, GPIO16. Not a record, but it's enough for many projects.

ESP-04 "external interface" consists of 14 pads arranged in two rows on the opposite sides of the board. For some reason the manufacturer left one pad not connected anywhere. (Why not to make one more GPIO pin available?)


ESP8266 ESP-201 module - antenna troubleshooting

ESP-201 external monopole antenna with U.FL connector
ESP-201 external monopole antenna
(λ - 2.4GHz wavelength - 125mm

ESP-201 module has two antenna options:

  • on-board so-called "inverted F antenna"
  • external antenna plugged into U.FL connector

The antennas are not intended to work simultaneously. By default ESP-201 board has external antenna selected. To use on-board antenna, the jumper (0 Ohm SMD resistor) should be resoldered as shown on the following pictures.

ESP8266 ESP-201 module - freeing up GPIO9 and GPIO10

Despite the fact ESP-201 module has D0, D1, D2, D3, CLK, CMD (GPIO6-GPIO11) pins broken out they provide interface to flash chip and cannot be used as regular GPIOs.

An attempt to assign GPIO function to any of these pins, e. g.


will definitely cause module hangup or reboot during the subsequent flash access.

Since it is supported by both ESP8266 and flash chip (25Q40B) the Quad I/O SPI flash interface can be downgraded to Dual I/O SPI thus freeing two data lines (SD_DATA2 and SD_DATA3) and making them available as GPIOs (GPIO9 and GPIO10, marked as D2 and D3 on ESP-201 board).

ESP8266 ESP-201 module - first impressions

ESP8266 ESP-201 module

I've been experimenting with different ESP8266 (mostly ESP-01) modules already for some time. As soon as ESP-201 became available I ordered them and yesterday received the long awaited package. And I was not disappointed. The ESP-201 module is a really good choice for prototyping ESP8266 projects.

The size of the board is 25x35mm, totally it has 26 pins with 0.1' (2.54mm) pin spacing. ESP-201 is equipped with on-board antenna and U.FL connector for the external antenna, which also was included in package.

Compared to ESP-12 this module has 6 more pins broken out - D0, D1, D2, D3, CLK, CMD (GPIO6-GPIO11).