In this how to guide on Using ESP IDF with STPM32, we are going to build Smart Meter IoT Application Software. This will use SPI interface for communication between esp32 wroom32 and STPM32/33 energy metering application. Using this sample code I will show you how to build mobile application for smart energy meter with Metrology Accuracy of class 0.2. In Indian households most of the energy meters are of accuracy class 1. After reading this guide you will know how to build digital energy meter suitable for advanced metering infrastructure (AMI) and is compatible with smart grid communication technologies with support of distributed generation (DG). Building smart meter IoT application software requires four things, hardware, firmware, mobile application software and webserver.