A precursor to the GTEM Energy Monitor project, was the amalgamation of an ESP8266 and CT Clamp (YHDC Current Transformer SCT-013), which was used to provide feedback of power usage to Domoticz.

Many such projects exist in this area but for a particular requirement, I wanted this to also be portable and not rely on an external power supply.

In addition for another ongoing project, a current clamp extender was required for the Grid Tie Inverters (principally the SUN-1000GTIL2 and SUN-2000GTIL2). GTIE would in effect also be used as the 'current clamp sender' and the forthcoming GTIL project would be the 'current clamp receiver', this board connecting to the GTIL2 Inverter current clamp input and RS232 port in order to gather additional information from the GTIL Inverter.

To extend this project further, it has an OPTO input for optionally reading the Electric Meter kWh flashing LED. For this, a 3DU5C Phototransistor, TSL257 Photodetector or lower sensitive GL5528 Light Dependent Photoresistor can be attached.

As the project also needed to be battery powered, a deep sleep link was added to the board, being powered from a CR123 Lithium Battery, the project can be housed in a small 85x58x33mm enclosure for completeness.