Here analog energy meter is replaced by a digital energy meter. The digital energy meter used here is a high accuracy, low cost, single phase power meter based on the ADE7757.The meter is designed for use in single phase 2 wire distribution system. A relay is connected in between power lines and the load. The relay is controlled by the primary controller.
Microcontroller 89C51 acts as the primary controller. The primary controller collects information from digital energy meter as well as from the smart card. Smart gives information about the limitation of units. The digital energy meter reading is compared with the smart card information by the primary controller and hence suitably primary controller controls the relay.