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Wireless Power Measurement System Group 2 Manuel Rodriguez Frank Ladolcetta Amir Shahnami Alex Demos Project Description Meter that will measure the power consumption of household appliances Meter information will be sent wirelessly to an LCD display Display the approximate daily and accumulated power consumption of the appliance being monitored Capacity to turn appliances on and off directly from the head unit Project Motivation Keep track of energy usage in order to use less energy and spend less money Prevent surprising power bills at the end of the month Corroborate energy savings of “energy efficient devices” Make a system that is user friendly Project Overview Design a circuit that measures current and voltage Create program to calculate power Program the wireless transceivers to communicate with each other and transmit the sensor information Design a circuit to display information on LCD Create program to display information Project Specifications No more than 10% accuracy error Keep cost as low as possible Wireless transmission should be no less than 30 feet Measure current up to 7A Measure voltage on a 120V wall outlet Block Diagram of System Wall Outlet Relay Voltage Measurement Current Measurement Microcontroller Wireless transmission Microcontroller Display Meter Overview Build Requirements Meter circuit design should be safe and reliable Design a circuit that is both cost effective and efficient Build a meter circuit that draws a low amount of power Power measuring methods • Voltage measurement using a voltage divider • Current measurement using a current sensing resistor • A pair of optoisolator to isolate and amplify the signal Powering the circuit The circuit is powered using 2 transformers that each go through a full wave rectifier and finally through a 5 volt voltage regulator. A transformerless circuit was tested but it was not as reliable as the circuit with the transformer. Voltage measurement Voltage will be measured directly from the house wiring A voltage divider is used to bring down the voltage to a level usable by the optoisolators Filters are added to eliminate high frequency noise in the circuit Current measurement Current sensing resistor will be installed in the neutral side of the outlet wiring to measure voltage drop A hall effect sensor was considered but it is too expensive A current transformer was considered but it is a less accurate method and more expensive Component specifications 2 resistors; a 2Mohm and a 1kohm with a 5% tolerance and a power rating of 1/4 watt A .025 ohm current sensing resistor with 1% tolerance and rated at 3W 12A, 240V relay Avago Technologies HCPL-7520 linear optoisolator Main Unit & LCD Diagram of device LCD display requirements One row to list the information to identify what is displayed on the screen. Three rows of data pertaining to three separate sensor devices. Must have a traversable menu to view up to 50 different sensors. Must display power consumption data in terms of dollars spent. Simple character display method. LED backlight for nighttime use. Low power consumption. (< 3W typical) Low price. (<$50) Readily available. LCD Specs & Technical Data • 4 lines x 40 characters • 2 - HD44780 equivalent • • • • • • microcontrollers 190mm x 54mm x13.6mm 18 - 2.54mm pins (14 Logic, 3 Supply, 1 NC) Requires a 5.0V Power Supply 11 Built-in instructions 5V, 1.2mA typical for LCD (.006W) 5V, 360mA typical for Backlight (1.8W) NHD-0440AZ-FL-YBW Reprinted with permission of Newhaven Display International Push Buttons/ Switches We require four tactile (pushto-make) pushbuttons on the front of device. Two of these buttons will be used for movement within the LCD menu. One pushbutton will disconnect supplied power to selected appliance. One pushbutton will allow the user to enter the menu. We also require a Single pole, single throw switch on the side of the device to control the LED backlight. Pushbutton Examples Reprinted under creative commons 3.0 license SPST Example Reprinted with access from public domain Instruction List Instructions To operate, the device has 2 separate internal microcontrollers to display to the LCD. A specific instruction must be selected by the main microcontroller and sent to the eight data pins. When the instruction is sent, the device must be enabled on the selected microcontroller (E1 or E2) to have the device complete the instruction. If characters are to be displayed, the RS pin must be set on and the device will output the selected character to the specified location designated by the set address command Reprinted with permission of Newhaven Display International Coding • • • • The Arduino microcontroller uses C programming language, and provides libraries for use with their product. The code will start off with an initialization section for initial powering up of device. The device will then display the data every minute from the MC in a line by line fashion to ensure all sensors are updated. Separate functions will be called for cursor movement, menu setup, and sensor power down. Coding example (Turning device on) Int main(void) { lcd_top.setCursor(0,0); lcd_bottom.setCursor(0,0); lcd_top.print("Please enter days in cycle."); lcd_top.setCursor(0,1); lcd_top.print("Use Up to go left"); lcd_bottom.print("Menu to advance:"); lcd_bottom.setCursor(0,1); delay(1500); } Microcontroller Design Microcontroller One single type of microprocessor for both applications Both applications use ATMega168 with a preloaded bootloader. Programmed with a USB to serial adapter. 6 analog input pins 14 digital input/output pins 1.8 to 5.5 volt operating voltage Programmed with Arduino software v. 0018 using C/C++ Each pin draws up to 0.22W (from 40mA), VCC draws up to 0.275W (from 50mA) Reprinted with permissions from Sparkfun Main Unit Programming • Initialize the LCD display to properly display all information • • • • • • needed Enter a setup prompt for the price per kWh and be able to re-enter this setup at any time Dynamically allocate ID numbers to each individual sensors Communicate to a specific sensor once an ID has been established. Sends information as floats to ensure both accurate values as well as smaller information size Updates LCD information as information from sensors are received Able to store a running total of money spent regardless of device status Sensor Unit Programming • Requests an ID from the main unit. • Constantly measures both voltage and current and averages power over 15 seconds. • Sends both an ID as well as power to the main unit to ensure individual device recognition • Sends information as floats to ensure both accurate values as well as smaller information size Main Unit Schematic • Powered by AC to 5V DC converters not shown • Pull down resistors to prevent button inputs from floating high. • Pull down resistors to the XBee header Sensor Schematic • Receives 2 separate power supplies through AC to 5V DC converters. •Pull down resistors to the XBee header. •Status LED and relay are controlled directly from the microcontroller. •7A fuse added to the circuit. Wireless Communication XBee Specs •We looked at four pieces of technology for this project: Zigbee, Bluetooth, WiFi, and XBee •Xbee Series 1 •$19.00 per unit. •The range was good enough for the group having a max range of 100ft (30m) •24.38mm x 27.61mm XBee Specs Transmission rate of 250kbps It is an RF transceiver and it runs at 2.4 GHz, which is the norm for this kind of device. • Voltage range from 2.8 to 3.4V. • The current: • when receiving data it is 50mA, • while transmitting information, the current is flowing at 45mA • while it is in power-down mode it runs below 10µA. • • XBee Adapter • • • $10/kit Connects to microcontroller Cord connects to computer to program the chip Programming of XBee • Using the AT command mode with X-CTU program is how the XBee chip will be programmed. • AT commands deal with all things from setting the sleep mode to resetting the chip. • The command below is a sample command that will display the lower 32 bits of the address. Programming of XBee (cont.) For the XBees to communicate to each other, the following need to match with the parenthesis being what we are using: – the Personal Access Network (234) – the BAUD rate (9600) We set up an Association network, which is like a peer-to-peer network with one device being the head unit. Block Diagram of XBee Example of how data is received from one device and then sent to another Testing Testing Procedure The device will be tested against a commercial Kill-A-Watt power monitor, which is rated at 99.8% accuracy. We tested the various levels of power consumption using a light bulb rig with 4 bulbs in parallel. Then, each power consumption level will be tested in comparison with level displayed on the Kill-A-Watt power monitor and will be graphed for an accurate comparison. Accuracy Results 450 400 350 300 250 Power Meter Kill-A-Watt 200 150 100 50 0 Timeline, Budget and Completion Summary Timeline Our timeline for Senior Design was based on bimonthly goals, however due to unforeseen consequences our timeline changed slightly. April 30th: Complete Research & Documentation May 31st: Have a good understanding of all aspects concerning the project June 1st: Begin testing parts, working for an accurate and quality design July 8th: All parts tested and working July 9th: Order PCB July 19th: Begin attaching parts to PCB July 24th: Have all parts put together July 30th: All parts tested and working which gives us a week prepare for the final presentation Workload Senior Design 1 Senior Design 2 LCD Design 5 Microcontroller 2 Wireless 8 Power Supply 16 Power Measurement 190 Documentation 180 15 PCB Design 5 Troubleshooting/Soldering 50 Project Boxes 25 Coding 60 TOTAL 180 376 Work Distribution LCD Design Frank Manny Alex X X Microcontroller X Wireless X Power Supply X Power Measurement X X Documentation X X PCB Design Project Boxes Coding Amir X X X X X X X X Approximate Budget Item Spent ($) LCD Design $ 85.00 Microcontroller $ 400.00 Wireless $ 270.00 Power Supply $ 60.00 Power Measurement $ 150.00 Documentation $ 15.00 PCB Design $ 60.00 Project Boxes $ 30.00 RLC $ 85.00 Hardware $ 100.00 TOTAL $ 1255.00 Completion Summary Design Parts Acquisition Software Prototyping / Testing Presentation 0 10 20 30 40 50 60 70 80 90 100 Questions?