How it Works

IoTaWatt measures each circuit using a passive sensor that clips around one of the insulated wires of the circuit and measures the magnetic field created by current passing through the wire.  The output of the current-transformer (CT) is low voltage and plugs directly into one of the device's 14 inputs.  From the browser based configuration app, 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.

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

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.

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

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.

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 was possible to structure 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, seems to be stable and 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. IoTaWatt has some unique innovations enabled by the nodeMCU capabilities, but the fundamental concepts of power measurement were learned from the Open Energy Monitor project.

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 to respond to demand for the 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 eventually offset by sales. IoTaWatt, Inc also supplies parts to Open Energy Monitor who assemble and sell a CE only version worldwide.

The short term goals of the project are to improve the documentation, add support for PVoutput, develop more local analytic applications, and develop the community support infrastructure. Long term, porting the firmware to the ESP32 or possibly an ARM platform would be an interesting project.

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