How it Works

IoTaWatt measures each circuit using a passive sensor that clips around one of the insulated wires of the circuit to measure the magnetic field created by current passing through the wire.  The output of the current-transformer (CT) is low voltage and plugs into one of the device's 14 inputs.  From the browser based configuration app, you select the model CT that is connected. IoTaWatt knows how to interpret the signal from the device to produce an accurate measure of the power being used at any moment.

How it Works

IoTaWatt measures each circuit using a passive sensor that clips around one of the insulated wires of the circuit to measure the magnetic field created by current passing through the wire.  The output of the current-transformer (CT) is low voltage and plugs into one of the device's 14 inputs.  From the browser based configuration app, you select the model CT that is connected. IoTaWatt knows how to interpret the signal from the device to produce an accurate measure of the power being used at any moment.

Measures 14+ circuits

Standard 3.5mm stereo jack input for 14 input channels. Each input is typically one current-transformer measuring one circuit, but a single CT can be installed to monitor multiple circuits, and/or several CTs can be combined into a single input.

Intuitive Configuration

All of the inputs are listed with the current name, CT type, and various options.  To edit, click on the input number.

Change the name, or specify a different CT model from the dropdown list.  Save and IoTaWatt begins using the new configuration immediately.

Comprehensive Status Display

The status of inputs and outputs is updated continuously.  Outputs can be defined to make additional details available.  The status of server uploads and context of the data-logs is available in drop-down tabs.

Integrated Analytic Tools

Integrated analytic tools allow viewing usage graphically. Show total power use along with individual circuits by selecting from a menu.

This graph app runs directly from IoTaWatt's web server. It was adapted from OpenEnergyMonitor's Emoncms system, which is well integrated with IoTaWatt.

Uploads to influxDB and Emoncms

More sophisticated users can configure data upload to influxDB and use Grafana or one of several other visualization tools to create stunning dashboards.

There is also an option to upload to the Emoncms system with it's own integrated graphical tools.

Emoncms dashboard

grafana dashboard with influxDB data source

Both of these external databases are open-software and available as commercial services or hosted on various personal platforms including windows and RaspberryPi.

PVoutput live-status display

Uploads to PVoutput

PVOutput is a free online service for sharing and comparing photovoltaic solar panel output data. 
Output data can be graphed, analysed and compared with other pvoutput contributors over various time periods.

While pvoutput is primarily focused on monitoring energy generation, it also provides equally capabable facilities to upload and monitor energy consumption data. Both solar generation and energy consumption data can be combined to
provide a 'Net' view of energy being either generated or consumed live.

Simple Powerful Scripting


The "calculator" is IoTaWatt's simple interface for creating scripts to combine and export data. You specify the units to calculate (Amps, Watts, Volts etc.) and then enter the function to calculate the value. It's as easy as using a basic four-function calculator.

Three Phase Capability

IoTaWatt can handle three-phase power in several ways.  The easy way uses just one voltage/phase reference transformer plugged into any of the three-phases.  Power measurements on the two other phases are made using a "derived" three-phase reference signal.

For utmost accuracy, two additional transformers can be connected to inputs for "direct" voltage and phase reference of all phases.

Fully Certified

IoTaWatt has been tested for compliance with regulatory and safety standards of North America and Europe including:

  • Compliance with FCC part B
  • CE compliance including Radio Emissions Directive (RED) and Low-voltage Directive
  • Low-voltage safety standards for US (UL) and Canada (CSA).  Testing and certification by Intertek and bears the ETL certification mark.
  • Accessories sold by IoTaWatt, Inc are UL listed or UL recognized and listed for use with IoTaWatt.

About the IoTaWatt Project

The project grew from an informal effort to produce a versatile electric power meter that was easier to configure and use. Employing the popular and powerful ESP8266 nodeMCU chip, it has an operating environment with a modular approach to data collection, storage, and reporting along with an integrated WiFi web-server. The resulting firmware, after more than a year of development, is very robust.

Early efforts concentrated on using available kit boards and shields with a minimum of custom hardware. Eventually, it became obvious that a single custom board was needed to provide the platform necessary for the software to be useful. The current open-hardware design is commercially produced.

Although the schematics and PCB layout are open and available in the project Git, there is a lot more to making a viable commercial product. IoTaWatt, Inc. is a legal entity that was established in response to demand for production hardware. The basic device, as well as related equipment, can be purchased by using the “Buy” tab above. The costs to develop and certify the hardware were substantial and hopefully will be offset by sales.

The short term goals of the project are to develop more local analytic applications, and develop the community support infrastructure. 

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