CWX ESP8266 BME280 v2 – Specification


CWX 2 –  Compact Weather Station IoT Home Automation


This CWX-2, Compact Weather Station for IoT Home Automation, is great for either indoor and outdoor use.

  • Designed to be battery powered, via a standard CR123A Lithium Battery, or from an external DC supply.
  • Allows remote sensing and sending data over Wi-Fi, such as to Domoticz or another Home Automation system.
  • The board is designed to fit into a Waterproof Clear Cover Enclosure, available separately.


CWX v2 specification overview:

  • Bosch BME 280 Module
    • Barometric Pressure 300…1100 hPa (millibar)
      • Accuracy ±0.25%
        • which is equivalent to 1m at 400m height change
      • RMS Noise 0.2 Pa
        • which is equivalent to 1.7 cm
    • Temperature -40 to 85°C
      • Temperature coefficient offset ±1.5Pa/K.
        • which is equivalent to ±12.6cm at 1 °C temperature change
    • Humidity
      • 0 to 100 %
      • Accuracy tolerance ±3% relative humidity
      • Hysteresis ≤2% relative humidity
  • SFH2440 Ambient Light Sensor
    • Light Level Spectral sensitivity
      • Std. Light A; T = 2856 K Minimum 7 nA/lx
      • Spectral range of sensitivity λ10% typically 400 to 690 nm
      • Wavelength of max sensitivity λS max typically 620 nm
  • Battery Voltage Monitor
    •  ADC switching provides a separate battery voltage reading
  • Powered by:
    • 1 x CR123 Lithium battery
    • External DC such as USB 5V
  • Connections
    • USB (CH340)
    • I2C (expansion)
  • Display
    • An optional OLED display can be connected to the I2C header
  • Enclosure


An example of the output can be seen here  as highlighted below.

Based on the industry standard ESP8266 (ESP-12S Series), the SDK includes:

  • BME-280, to provide a low power
    • Barometric Pressure, 300-1100 hPa
    • Temperature, -40 to +85°C
    • Humidity, 0-100% Relative (± 3%)
  • SFH2440, to provide a high linearity Ambient Light Sensor.
    • Spectral range of 400 to 690 nm



The CWX has four headers.

  • BMx Sensor header
  • Micro USB (for flashing and development)
  • I2C (expansion)
  • DC In (5V)


Software Code

Arduino IDE based software / firmware code for this CWX ESP project will be provided in our Wiki, to easily get you up and running.  This code connects the CWX to your Wi-Fi and then uploads to a ThingSpeak channel.  FREE ThingSpeak accounts for small non-commercial projects are available (providing up to four channels), so you could have more than one project running at once.

The CWX-2 has been designed with an in-board ‘Wemos D1 Compatible’ USB interface, which includes a standard Micro USB Socket.


This board will work with all three BMx sensors, including the low cost BMP180.  However, in order to get Humidity and better resolution, you require to use the much better BME280 – which is included with our CWX-2 SDK Kit.

Further reading on BME280.



The CWX PCB has cut-out to allow the BME280 sensor to fit flush and also the light sensor to be swapped facing up (PCB top) or down (PCB bottom).  (Default is up).



The CWX PCB is designed to fit into a standard 85x58x33mm Waterproof Clear Cover Plastic enclosure


3D printed enclosures can also be downloaded free of charge, resized if needed. and used for this project.  Examples below:


Battery Holder

The CR123A Battery Holder is supplied with the SDK but can be optionally soldered as needed.

It has a locating pin, to aid correct fitting.

Note: What is the difference between CR123 and CR123A?  There are no difference between CR123 and CR123A batteries. They have the same size, only their names are different because CR123A is a most common name.


In the Box

CWX-2 ESP8266 board.

You will need to update the firmware with your preferred open source firmware, using a standard micro USB cable (not included).  Working examples of test code can be found in our Wiki

  • 1 x CWX-2 ESP8266 Board
    • SMD (Surface Mounted Components) Populated.
    • Fully Tested
  • 1 x BME280 Module
  • 1 x Strip of straight pin header
  • 1 x CR123A Battery Holder (Not Soldered)


Battery not included

  • Due to potential shipping restrictions and being readily available, a standard CR123A Lithium Battery is not included and should be sourced locally.


Important Foot Note.

These Wiki pages are MOVING to the GitHub Wiki.   Simply select a repository pertaining to the board and click Wiki.


Other Details

Further information on this product may be found in our downloads and Wiki pages.  Other technical information and code examples are also shared in our GitHub Pages.  Project information may also be found on

We value our customers and should you have any other questions, please feel free to contact us.

Leave a Reply

This site uses User Verification plugin to reduce spam. See how your comment data is processed.

Cart Summary (Discounts shown at checkout)

    Product Price Quantity Subtotal

Basket totals

Subtotal £0.00
Total £0.00