Smart system sets up a platform for electricity meters and smartphones to dance together (Part 1)

Today, smartphones are entering almost all markets, bringing consumers greater intelligence and efficiency. Consumer expectations have increased several fold, requiring all information to be available at the touch of a button, and this demand has motivated designers to integrate smartphones into various systems designed today.

　　Today's consumers are particularly concerned about energy efficiency and expect to minimize energy costs and related carbon emissions. Energy-efficient solutions that are energy-saving and environmentally friendly have a competitive advantage and help maintain the sustainable development of the ecosystem model.

　　How to monitor energy consumption and costs?

　　Electricity meters have evolved from mechanical systems to electronic smart meters. Smart meters now monitor not only the total electricity consumption of a household, but also the power consumption of each appliance. For example, some appliances currently on the market have built-in meter functions that can monitor the power consumption of home appliances; smart sockets can monitor the power consumption of connected appliances. Some smart meters provide some kind of network communication interface to support centralized or remote meter reading functions.

　　How to check home electricity usage information on smartphone?

　　Text messages are the easiest way to display electricity usage data on a smartphone. However, text messages are not very convenient when long-term monitoring of electricity usage is required, and text messages have certain limitations if users want to view chart data.

　　What is the solution?

　　Near Field Communication (NFC) is an emerging smartphone connectivity technology that enables mobile phone users to exchange data over a short distance (a few centimeters). NFC tags can exchange data with NFC devices without the need for power.

　　NFC devices share the same basic technology with short-range (13.56MHz) radio frequency identification (RFID) tags and contactless smart cards. The International Organization for Standardization/International Electrotechnical Commission (ISO/IEC), the European Telecommunications Standards Institute [ETSI] and the European Information and Communication Systems Standardization Association (ECMA) have accepted this standard. The communication distance between an NFC reader and an NFC tag is less than 4cm, and a payload of data can be exchanged between an NFC tag and an NFC reader or between two NFC devices.

　　This technology allows users to easily access and store electricity usage data from smart meters. NFC smartphones can read data from NFC tags (NFC passive devices), and consumers can then view electricity usage analysis curves and other meter information on their phones.

　　How can we enable a smart meter to have a simple NFC interface?

　　Today, there is a dual-interface electrically erasable programmable read-only memory (EEPROM) [3] on the market. This innovative RFID product can connect to any microcontroller via the I2C bus, enabling the smart meter solution to have an NFC interface. The host device can read and write to the dual-interface EEPROM via the I2C or RFID interface. When the smart meter uses this dual-interface EEPROM, the smartphone can directly read the electricity consumption data for a fixed period of time, and then interpret and display the electricity consumption data in a graphical way so that electricity users can understand their electricity consumption.

　　How to design a smart meter?

　　When we install a dual-interface EEPROM in a smart meter, the EEPROM acts like an NFC tag of the NFC-V class and supports the ISO 15693 standard. The energy meter continuously records the monthly electricity usage information and other important electricity usage data on the dual-interface EEPROM. The Android application can read the monthly electricity usage data and compare the electricity usage in a chart. Below we will introduce the application software we developed for the above needs in detail.

STMicroelectronics' Energy Meter Platform

　　STMicroelectronics has multiple single-phase or multi-phase energy meter reference designs. The energy meter industry is moving from basic designs to advanced energy meters featuring wide-range high-precision current measurement, fast digital calibration, anti-data tampering, and anti-meter tampering. To meet these market needs, STMicroelectronics has launched an electronic energy meter reference design platform. The following functional diagram describes this smart meter platform:

　　Figure 1: Smart meter

　　STEVAL-IPE020V1：

　　The STEVAL-IPE020V1 is a single-phase energy meter based on the STPM10 meter chip and the STM8L152C6 microcontroller, with an M24LR64 dual-interface EEPROM memory built in. This is a full-featured single-phase meter solution equipped with parameter display, anti-meter tamper management, maximum demand (MD) calculation, dual interface (radio frequency (RF) and integrated circuit interconnect (I2C) [5]) EEPROM data logging and low power management. This energy meter supports the IEC 61036:1996 + A1: 2000, static meter for active energy class 1 for Ib=10 A international standard. In addition, the energy meter has multiple anti-meter tamper detection functions: absence of ground and neutral wires, reverse polarity, chassis tampering and magnetic tampering.

　　Figure 2: STEVAL-IPE020V1 single-phase electricity meter with built-in dual-interface EEPROM

　　System function diagram:

　　Figure 3: Functional block diagram of the STEVAL-IPE020V1 single-phase energy meter

　　The block diagram describes the system architecture:

　　STM8L152C6T6: STMicroelectronics' ultra-low-power microcontroller [MCU], which is responsible for all data management and power management tasks, consumes much less power than similar products, and has a built-in real-time clock [RTC] for data and time management.

　　STPM10BTR: The programmable single-phase energy meter chip [IC] is connected to the microcontroller via a three-wire serial peripheral interface [SPI]. The STPM10 meter IC provides active energy, apparent energy, instantaneous voltage and current, and automatic calibration functions.

　　Dual-interface EEPROM M24LR64-RMN6T/2: connected to the microcontroller via the I2C bus. This is a dual-interface EEPROM that can communicate with I2C devices via the I2C bus (wired) and with RF readers (NFC smartphones) via the RF radio frequency interface (wireless). The memory can record various important parameters such as cumulative power consumption, maximum demand, average power factor, and anti-meter tampering information for 7 consecutive months.