WattVision Base v1.0

This design accepts an LPC1768 mbed module, and was created with a couple of primary purposes in mind, so is what I'd call a 110% design. With some small changes in component population it could serve a few needs, and it has an expansion interface, to scale it further than shown here.

Spare PCBs for sale

The PCB price was right to buy 10, even though plans were to build 5 devices. If you have interest in a bare PCB for $16 + shipping, contact me and check if I still have them.


See also SmartBoard for general purpose usage.

Virtual Build /media/uploads/WiredHome/wattwatcher.png

Primary Purpose

  • Monitor electrical energy consumption using current transformers (e.g. Split-core sensor) with 3.5 mm plug.
  • Scaleable (to 48 total channels):
    • 16 "base-board" channels.
    • Design supports expansion up to 2 "daughter-boards".
    • Each Daughter-board has 16-channels.
  • Alternate interface with 2-pin screw terminals.
  • An additional circuit (on the far-left) wires directly to the split 240v line to sample the voltage and is then electrically isolated from the rest of the circuitry. This is done with a separate micro and opto-isolator.


As originally designed as a device that is intended to monitor electrical energy, it may commonly be connected in or near an electrical breaker panel, and connected to the line voltage, which can be lethal.

Only those familiar with working with high voltage should work this project in that configuration.

Power Source

  • PoE module, or USB adapter, or screw terminal.

Other features

  • micro SD card slot
  • USB Host (e.g. for memory stick)
  • RTC battery holder
  • Display adapter (3 connectors) (see RA8875 display)
    • 4-wire SPI for display
    • I2C for Capacitive touch
    • 4-wire SPI for display mounted micro SD
  • Small relay
  • On-board Temp/Humidity sensor (this is definitely the most challenging part to solder)



  • Shown is version 1, which is the only version that has been built.
  • 5 Units were built with slightly different purposes.
  • A few errata exist on this version, which would improve flexibility and usage. See the user-guide for known issues.

Versions built

  1. Electric Water Boiler controller - in use. This version monitors 10 thermostat controlled zones, and gates the demand request to the boiler. It can then monitor the boiler as the 3 stages of heating elements activate. This version also has an RA8875 touch-display, to monitor and adjust some of the behavior.
  2. Garage Door controller - in use. This version does not populate the left side of the PCB. It is powered from the PoE module, and monitors the state of the garage door. It [optionally] sends email on door open/close/stuck/open-a-long-time events, as well as high temp alerts. It hosts a web page which permits seeing the status and remote open/close-ing the door.
  3. Electrical Energy monitoring - still "in the lab".

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