The WeMos D1 mini was developed for the tinkerers. It's based on the ESP8266 chip. There are many cool DIY projects that you can achieve with this board. It's very similar to the Arduino, has a built-in WiFi, and much cheaper (around $3 on eBay).

I currently have 2 of these, and I will be using them soon in 2 home projects.

The ESP8266 chip is soldered on the front side. It has 16 pins and a WiFi antenna.

Front of the WeMos D1 mini

On the back, we find the micro USB connector, a USB to serial interface "CH340G", a voltage regulator, a reset button, a 12MHz resonator, and a fuse.

Back of the WeMos D1 mini

ESP8266-12S

The ESP8266 has a single core 32-bit CPU that runs at 80 MHz.

  • 4MB Flash
  • 3.0 ~ 3.6V (recommendation 3.3V)
  • 80mA Nominal working current
  • 802.11 b / g / n
  • 2.4GHz-2.5GHz (2400M-2483.5M), PCB trace antenna
  • UART / HSPI / I2C / I2S / Ir Remote Control / GPIO / PWM
  • 24 x 16mm PCB, 2x8 castellated connections
  • Operating temperature: -40°C ~ 125°C

CH340G

The "WCH CH340G" is an USB to UART interface. It provides a virtual serial port to a PC. The role of this chip is to make communication with the ESP8266 easier. No need for a separate FTDI serial adapter.

The resonator schematics:

Here you can find the pinout of the chip (the grayed pins are not used):

Pin# Name Direction Comment
1 GND Power Ground reference of the chip. Connect to the ground of USB bus.
2 TXD Output UART Data Transmit output.
3 RXD Input UART Data Receive input.
4 V3 Power Internal 3.3V reference for USB physical layer. Decouple with a 4.7-20nF capacitor when in 5V operation, or tie to VCC when in 3.3V operation.
5 UD+ Analog USB D+ signal.
6 UD- Analog USB D- signal.
7 XI Input Input of the crystal oscillator. Connect to the crystal resonator and load capacitors.
8 XO Output Output of the crystal oscillator. Connect to the crystal resonator and load capacitors.
9 CTS# Input UART flow control signal Clear to Send.
10 DSR# Input UART flow control signal Data Set Ready.
11 RI# Input UART flow control signal Ring In.
12 DCD# Input UART flow control signal Data Carrier Detect.
13 DTR# Output UART flow control signal Data Terminal Ready.
14 RTS# Output UART flow control signal Request to Send.
15 R232 Input Auxiliary RS232 enable. Active high, internal pull down.
16 VCC Power Supply rail for the chip.

ME6211 Voltage Regulator

  • has a maximum output of 500 mA.
  • Operating Voltage Range: 2V~6.0V
  • Low Power Consumption: 40 µA
  • Standby Current: 0.1 µA

In the next post, we will see how to connect the WeMos to a PC, and upload programs using the Arduino IDE.