Application Note. Energy Meter LAN Interface

Transcription

1 Application Note AN2xxx Energy Meter LAN Interface Author: Sunil Jha Associated Project: Yes Associated Part Family: CY8C27xxx PSoC Designer Version: 4.10 Summary Automated Meter Reading (AMR) now a day become quite popular and implemented in most of the countries. This project is an effort to develop a low cost Local Area Network (LAN) interface to Energy Meters for automated meter reading and energy distribution management. A three wire output interface is taken from existing electronic energy meter based on Analog devices ADE7751 chip. This output is then connected to the Energy Meter LAN Interface board developed around Cypress PsoC CY8C MOXA Technologies Serial to Ethernet module NE4110S is configured as UDP client to send data packets containing unique meter identification number and energy consumption data at periodic interval. A server side PERL script receives and parses the data to store in Microsoft access database. This database is then further made accessible to the users and managers through Internet web server for online access. Introduction The idea of interfacing Energy meters on LAN originated from practical difficulties faced in periodic meter reading and regular billing. In this project a low cost simple LAN interface for energy meters is designed, developed, and tested for automatic meter reading and making them available online. At the heart of the design is Cypress PsoC CY8C27443 controlling all on-board devices. MOXA Technologies NE4110S Ethernet network enabler is used to transmit collected energy consumption data periodically over 10 Mbps LAN in the form of UDP (User Datagram Protocol) packets. The unique feature of the developed board is that it can be interfaced to multiple meters. The Dallas semiconductor s 1-wire 4kb RAM with counter DS2423 with 3-V lithium battery is used to count pulses from meter and store them. So data remains in the battery backed RAM even when the power goes off. Another advantage of using it is that it has two externally triggered low-going pulse 32-bit counters. In this way a single DS2423 can handle two energy meters independently. This has 1-Wire interface to outer world so any number of devices can be connected on single PsoC I/O pin. In multistorey apartments where cluster of meters are located at single place, a single interface board connect them all to LAN for automated meter reading at very low cost. Functional Description The Energy Meter LAN Interface board consists of a 16x2 alphanumeric LCD for status display, a CY8C27443 PSoC as main controller, a NE4110- S Ethernet network enabler for RS-232 devices, and DS2423 4kbit 1-Wire RAM with 32 bit counters. ADE7751 Energy Metering chip in Electronic meter sends a low going pulse at every 0.01 kwh energy consumption. This pulse is directed to counter A of DS2423 through MCT2E optocoupler. In this way energy consumption keep on accumulating inside counter RAM irrespective of PSoC functions. NE4110S is configured to transmit serial data in buffer after receiving delimiter # as UDP packet to server IP address. CY8C27443 after displaying welcome message on LCD, read DS2423 s 64-bit unique identification number and display it on LCD. This number is used to identify the meter whose consumption is reported by the interface board to the server. Every data UDP packet contains the 6/11/04 Revision A - 1 -

2 unique 64-bit meter ID and the energy unit consumed till that particular time. MAX233 is use to interface PSoC s UART to NE4110S RS-232 interface. PSoC is programmed to read DS2423 through 1-Wire interface and send data serially to NE4110S with ending # after predefined time interval. For testing it was set as 1 min, but for real implementation it is 1 Hr. On the server side, a PERL script captures the UDP packet and parses the unique meter ID and energy consumption data received and mark it with the time stamp. The data is then directed to be stored in the Microsoft Access Database for further processing. 16x2 Alphanumeric LCD NE4110S 10/100M Ethernet Network Enabler Module RJ45 MOXA Technologies CY8C27443 PSoC Invention Board M A X DS MCT2E From ADE7751 Figure 1: Functional block diagram of Energy Meter LAN Interface Hardware Description PSoC Invention board containing CY8C27443 with USB programming interface is used at the heart of interface board. The details of I/O pin usage of PSoC are: Pin P2 [0] P2 [1] P2 [2] P2 [3] P2 [4] P2 [5] P2 [6] P2 [1] P0 [5] P0 [6] P0 [7] Usage Description DB4 of LCD DB5 of LCD DB6 of LCD DB7 of LCD Enable pin of LCD RS control of LCD R/W control of LCD DB5 of LCD RxD of MAX233 1-Wire Bus TxD of MAX233 Lots of options have been explored before finally selecting the DS2423 as counter to store meter readings. The limitation with the use of microcontroller Flash or any external EEPROM is their Read/Write endurance limit. EEPROMs generally have 1,000,00 Read/Write cycle limit which restrict maximum meter reading that can be stored to 50,000 and after that EEPROM has to be replaced. This is the major bottleneck in their use. DS2423 has two main advantages i.e. firstly each device has unique factory-lasered and tested 64-bit registration number. This helps in identifying the individual meter in multiple interface environments. Secondly, It works independent of PSoC, without any need of interrupt generation on low-going pulse capture. Additionally it has 16 memory pages of 256 bits each and two page written counters, which can be used further to enhance capability of interface 6/11/04 Revision A - 2 -

3 board. The four main data components of DS2423 are: a) 64-bit lasered ROM, b) 256-bit scratchpad, c) 4096-bit SRAM, and d) four 32-bit read-only counters. Fig. 2 shows the block diagram of DS2423 control and memory sections. 1-Wire Bus 1-Wire Function Control 64-bit Lasered ROM Parasite Powered Circuitry Memory Function Control 256-bit Scratchpad Vbat SRAM 4096-bit A B RPI (256-bit pages) Page Write Cycle Counters Externally Triggered Counters Figure 2: Block diagram of DS2423 The RAM of DS2423 is to be backed up by 3V lithium battery but the triggered signal available from the energy meter is of 5V. Optocoupler MCT2E is used to isolate counter RAM circuitry from Meter pulse output and also for voltage shifting from 5V to 3V. MOXA Technologies NE-4110S Ethernet network enabler module for RS-232 devices is used to provide LAN connectivity to the interface board using in-built TCP/IP stack. The module is configured as UDP client with serial data parameters as baud, 1 stop bit, no parity, no flow control. The serial data delimiter is set as #. Once the module receives the # it packs all serial data received before and transmit on LAN in the form of UDP packet. The NE4110S module board pin interface is shown in Figure 3. MAX233 serial line driver is used to interface CY8C27443 UART TTL signals to NE4110S RS- 232 interface. Figure 3: NE4110S pin interface The complete circuit diagram is shown in Fig. 4 (in separate file EMNI_circuit.pdf). Actual photograph of interface board is also shown in Fig. 5. Software Description The software code for CY8C27443 is written in C using Image craft C compiler in PSoC Designer v4.1. The user modules used for the project are LCD Toolbox, UART, and One wire software OneWIreSW module developed by Wes Randall and downloaded from The complete PSoC Designer 4.1 project is attached separately with this submission. Figure 6. shows the program flow chart for the algorithm. 6/11/04 Revision A - 3 -

4 Figure 5: Photograph of working Energy Meter Network Interface board 6/11/04 Revision A - 4 -

5 START Display Welcome Msg. Read Counter ID. Display Counter ID. Read Counter A value. Display the Counter value in Hexadecimal on LCD. Transmit Counter ID and Counter value separated by comma. Transmit # Delay 1 Min or 1 Hr (Interval for taking reading) Figure 6: Program Flow Chart List of Required Parts Below is the list of parts used in the construction of the project: PSoC Cy8C27443 Invention Board MOXA s NE-4110S Ethernet Network Enabler Module MAX233 Serial RS-232 Line driver Optocoupler MCT2E DS2423 4kbit 1-Wire RAM with Counter 3V Lithium Battery Resistor 10K, 330 Ohm Capacitors- 1µF Acknowledgement I would like extend my heartily thanks to the whole Cypress and CMP team to organize this contest and sending PSoC invention board, without which its not possible to execute and implement my design idea. I would also like to thanks MOXA Technologies for providing NE-4110S, and Dallas Semiconductor for DS2423 Samples. 6/11/04 Revision A - 5 -

6 About the Author Name: Title: Background: Sunil Jha Research Scholar, Design and development of many embedded systems and robotics projects. Experience in microcontroller programming and hardware construction. Contact: Department of Mech. Engg, Indian Institute of Technology Kanpur , INDIA Cypress MicroSystems, Inc nd Street SW, Building D Lynnwood, WA Phone: Fax: / / support@cypressmicro.com Copyright 2003 Cypress MicroSystems, Inc. All rights reserved. PSoC (Programmable System-on-Chip ) is a trademark of Cypress MicroSystems, Inc. All other trademarks or registered trademarks referenced herein are property of the respective corporations. The information contained herein is subject to change without notice. 6/11/04 Revision A - 6 -