Total House Power Monitoring System

Design Report

Client: Herb Harmison

Advisor: James Triska Glenn Hillesland

Team: Sunil Varghese Ying Chiu Luk Adam Wheeler Matthew Gordon

May 03-18 December 10, 2002 Table of Contents

1. Introductory Materials - Abstract p. 2 - Acknowledgement p. 3 - Definition of Terms p. 4

2. Project Design - Introduction p. 6 General Background Technical Problem Operating Environment Intended Users Assumptions - Design Requirements p. 8 Design Objectives Functional Requirements Design Constraints Measurable Milestones - End-Product Description p. 9 - Approach and Design p. 10 Technical Approaches Technical Design Testing Description Risks and Risk Management Recommendation for Continued Work - Financial Budget p. 19 - Personal Effort Budget p. 19 - Project Schedule p. 20

3. Closure Material - Project Team Information p. 22 - Summary p. 22 - References p. 22 List of Figures

Figure 1: Hardware design block diagram Figure 1 Hardware design block diagram p. 6 Figure 2 Analog watt meter p. 10 Figure 3 Power triangle p. 11 Figure 4 Wattmeter schematic on incoming line p. 11 Figure 5 Diagram of final system design p. 12 Figure 6 Voltage measurement diagram p. 13 Figure 7 Diagram of current measuring circuit p. 14 Figure 8 The pin assignments for the 25-pin (left) and 9-pin (right) serial ports p. 15 Figure 9 Pin assignments for the National Semiconductor RS-232 driver chip p. 15 Figure 10 Circuit schematic of the RS-232 driver chip Connected to the 25-pin and 9-pin serial port cables. Also shown are the external capacitors required for the chip. P. 16 Figure 11 Diagram of the 5V power supply p. 17 Figure 12 Block diagram of system p. 18 List of Tables

Table 1: Power dissipation of resistors p. 13

Table 2: Financial Budget Estimate p. 19

Table 3: Financial Budget Actual p. 19

Table 4: Personal Effort Estimate p. 19

Table 5: Personal Effort Revised p. 19

Table 6: Gantt Chart p. 20 Introductory Material Abstract

Homeowners are currently unable to tell how total power consumption is distributed in the home. They also only get feedback of their consumption on a monthly basis. The Total House Powering Monitor System will allow users to monitor power consumption of one’s home in real-time. Hardware will be developed, using a wattmeter to measure the total power consumption. The data will be collected and sent to a user interface and a database for long-term trend analysis. The interface will give the user the option of setting alarms and monitoring total consumption. Acknowledgements

Mr. Herb Harmison and Mr. Glenn Hillesland have provided the team with guidance and great technical advice. Their contributions are greatly appreciated by the whole team. Definition of Terms

CT - Current transformer

PT – Power transformer

VA – Volt-Ampere

W – Watts

PC – Personal computer A/D – Analog digital converter Project Design Introduction

General Background The total house power monitoring system will allow a homeowner to monitor total power consumption within his or her home. A read out of real-time power consumption measured in Watts will be displayed on an interface similar to a thermostat. The same information will have the capability of loading onto a spreadsheet where it can be graphed.

Technical Problem Current monitored using a CT and voltage will be monitored using a PT. A microcontroller will collect the data and send it to the user interface for display and to the database for records. Through the combination of current and voltage, a power triangle can be calculated to determine the power factor. The user interface will have a numeric readout of power consumed and lights that will warn the user of high energy usage.

The hardware portion of the project will consist of a metering device that will plug in between an appliance and an electrical outlet. It will be connected to the PC via serial cable. The software will perform necessary calculations and record data to a file on the hard drive. The data will be useable on any compatible computer and can be analyzed by any graphing software.

Power Cord Power Cord Prototype

Wall Socket Appliance RS232 Cable

Computer

Figure 1: Hardware design block diagram

Operating Environment Shielding and protection from the elements is a non-issue because the intended location of the device will be indoors. The unit will possibly be in a fairly dirty environment with dust and other contaminants. The unit components will need an operating range between 40 and 115 degrees Fahrenheit. Intended User(s) and Use(s) The system will be used by homeowners for the purpose of monitoring power consumption of appliances and other electronic devices within the home. The system will not automatically control power consumption, only monitor it.

Assumptions - The unit will monitor U.S. Power (60 Hz, 120V lines). - The user will be familiar with operating a computer. - The user will have a basic knowledge of electricity and the concept of power. - The user will need an understanding of the utility rates in their respective area. - Limitations - The unit will have a single line read out. - The unit will limited in the max amps it is able to monitor. The small equipment needed for this project is the limiting factor. - The environment will be within the limits specified above. Design Requirements

Design Objective - Read current using a current transformer and a resistor network connected to an A/D to measure and digitize the voltage waveform.. - The interface should receive the data from the microcontroller and display it in a way that is easy for the user to understand. - The interface will have the ability to signal the user of a period of high power consumption. This can be done both visually and audibly. - A spreadsheet in Microsoft Excel will help the user see trends in power consumption.

Functional Requirements - Measure the total amount of power that is being consumed. - Display the power consumption to the user. - Allow the user to set alarms to warn them of high power consumption with lights and sounds. - Store the data collected to a database for analysis. This will be done by method of graphs and charts. - Have a reliable source of power. This is to reduce the risk of losing data when the unit is unplugged.

Design Constraints - Protecting the system from an over-current by having a fuse. - The monitoring system must fit easily behind appliances; the microcontroller must be small enough to mount near the unit. - The entire system needs to remain within a $100 budget.

Measurable Milestones - Check the resistor network to ensure accurate voltage measurement. (7.5 %) - Check the current transformer to ensure accurate current measurement. (7.5%) - Using a microcontroller, calculate the power consumption and send to the interface. (40%) - The interface is able to display the power consumption both with lights or a visual indicator along with the actual read out of consumed power in Watts. (25 %) - Communication via serial cable will be needed to transfer the measured values from the unit to a PC. (20 %) End-Product Description

The total house power monitor is a device that can monitor total power in a single home appliance as a function of time. Any number of portable units can be installed within the house. There will be a visual and audible method the unit uses to alert the user of high consumption situations. There is also the serial cable connection capable of loading information retrieved by the device into a spreadsheet for further analysis and recovery of data. Approach and Design

The measuring device can be done with one of two methods. It can be measured using analog devices or digital circuits.

One method is to have three analog devices. Voltage can be measured of the incoming power line. Current can be measured through the use of a current transformer. Watts can be measure utilizing a watt-meter.

The method that we are considering to implement is the digital circuit. The digital approach is chosen because we can create a smaller unit by building a circuit to measure current and voltage.

Technical Approaches - Monitor current with the use of a CT. The CT will reduce the actual current value to a corresponding value between 0 and 5 amps. - Monitor voltage through a network of Figure 2: Analog Wattmeter resistors. - Place the product between the wall socket and the appliance. - Use similar A/D converters to digitize the current and voltage measurements. - The A/D converters will then send the digital signal to a RS232 Driver. The driver is needed to send the data through the serial communication cable to the PC.

Technical Design: Analog Meter Approach - The use of CT’s and PT’s is a cheap and easy way to calculate current and voltage. - A wattmeter will be used to record the wattage for calculating a power triangle. The hypotenuse of this triangle can be calculated from multiplying the RMS voltage and the RMS current values together. The height of the triangle will need be calculated. The height of the triangle will represent the reactive power the appliance is using/causing. Figure 3: Power Triangle

- The display might be analog composition of all three devices, as shown in Figure 4. The interface will be made simple to start and add features dependent on time and money. More featured will add more interest.

Figure 4: Wattmeter schematic on incoming line..

Digital Circuit Approach - This approach is chosen because of its simplicity in hardware and software design. - In Figure 5 is a block diagram of the final hardware approach that is being implemented. The hardware has four main parts, the voltage measurement, current measurement, power supply, and the computer interface devices. The job of the hardware is to provide the computer with a scaled replica of the current and voltage waveforms that are feeding the load. This is done by scaling the current and voltage waves down to a 0 to 5V scale first. They are both then digitized by the A/D and sent to the computer by the RS232 driver. Neutral Hot CT Voltage Load Measurment Serial A/D Wall Plug Communication Hot AD7823 RS 232 Computer Neutral 5V Driver Gnd Input A/D DS14C232 5V Supply Current 5V Measurment AD7823

LP2954 Figure 5: Diagram of final system design.

Voltage Measurement - The voltage measurement section consists of a voltage divider and an analog to digital converter. The voltage waveform that is feeding the load cannot exceed utility tolerances of 5% shown in equation (1). The voltage divider is able to scale 0 to 180Vpeak down to 0 to 5Vpeak, which is the input range of the A/D.

120V *1.05 RMS  178V (Equation 1) 0.707 Peak

178VPeak  126VRMS (Equation 2) 2

- The large resistor of the voltage divider was chosen to be 1M for two reasons. The first is so power dissipation can be minimized which a large resistor helps. But in order to keep the noise from the operating environment out of the system a small resistor is needed. The 1M resistor value optimizes this trade off according to Prof. Patterson. Below in Figure 6 the schematic of the voltage measurement device is shown. Wall Plug Hot Hot Neutral Neutral Gnd Gnd 0

Pins 10K 20K 1M AD7823 Vin- A/D Vin+

Load Being Hot Gnd Neutral Measured Figure 6: Voltage measuring circuit.

- In the table that follows the value, tolerance, and expected power dissipation of each resistor is shown. Since a variable resistor has been included in the design loose tolerances can be used for the resistance values because they will be measured and any compensation can be done with the trim pot. Also since large resistance values were chosen the power dissipation is low and standard ¼ watt resistors can be used. It should also be noted that the internal resistance of the A/D is on the order of several M’s so it does not need to be included as part of the voltage divider.

Table 1: Power dissipation of resistors. Resistor Tolerance Current Power Dissipation 1 M Ohm 10% 0.175 mA 30 mW 20 K Ohm 10% 0.175 mA 0.612 mW 10 K Ohm 10% 0.175 mA 0.175 mW Current Measurement - The current measurement part of the hardware system is very simple, the heart of the design is a current transformer. The CR Magnetics split core current transformer 3110 was chosen because it was said to have a large linear operating range and relatively high accuracy while keeping costs low. A diagram of the current measurement hardware can be seen below in Figure 7. Wall Plug Hot Hot Neutral Neutral Gnd

Pins AD7823 Vin- 1K A/D Vin+

Neutral Gnd Hot

Load Being Measured

Figure 7: Diagram of current measuring circuit.

- The 1K resistor was chosen in accordance with the datasheet for the current transformer. It should dissipate .025 Watts of power so a ¼ watt resistor will work well. There will be a 5V drop across the resistors terminals at full scale which is 15A.

A/D Chip - The A/D chips should communicate to the RS232 driver, speed of communication should not be a problem since the A/D only run at 133,000 samples per second. The A/D was chosen for its cheap cost and adequate accuracy, 8-bit. This will allow 256 digital output values, which will provide adequate precision since they cover a 0-5V range. RS 232 Driver - The interface between the hardware and software is done using the serial port of the computer. This communication protocol is called RS232 and is a very common way to communicate with the computer. The pin assignments for both the 9-pin and 25-pin serial port are shown in Figure 8 below.

Figure 8: The pin assignments for the 25-pin (left) and 9-pin (right) serial ports.

- A National Semiconductor RS-232 driver chip, model number DS14C232, was chosen for the system because it has two channels for digital input. The two digital inputs to this chip are the outputs from the two A/D converters: one for current and one for voltage. The RS-232 driver chip converts the 0-5 V digital signal from the A/D to a –10-10 V signal required for the serial port. One output from the RS 232 driver chip is sent to the computer via a 9-pin serial port cable. The second output is sent to the computer via a 25-pin serial port cable. The pin assignments for the RS232 driver chip are shown below in Figure 9.

Figure 9: Pin assignments for the National Semiconductor RS-232 driver chip. - From the figure, pins 11 and 12, called Din1 and Din2, accept the digital input from the A/Ds. The 9-pin and 25-pin serial port cables are connected to pins 14 and 7, called Dout1 and Dout2. The entire circuit schematic of the RS-232 driver chip and the two serial cables is shown in Figure 10. +5 V

C1 + Vcc

V + Gnd 5 4 3 2 1 C1 - Dout1

C2 + Rin1 DS14C232 C2 - Rout1

V - Din1 9 8 7 6 From A/D Dout2 Din2 From A/D 9 Pin Serial Port Rin2 Rout2

13 12 11 10 9 8 7 6 5 4 3 2 1

25 24 23 22 21 20 19 18 17 16 15 14

25 Pin Serial Port Figure 10: Circuit schematic of the RS232 driver chip connected to the 25-pin and 9-pin serial port cables. Also shown are the external capacitors required for the chip.

- In the figure pin, C1+, C1-, C2+, and C2- are connected with external capacitors. The minimum value for the capacitor connected to those pins is 0.1 F. Power Supply - The power supply is needed because each of the three chips being used require 5V input and some require a 5V reference as well. The power for the system is taken off the 120V line that also feeds the load or appliance. The power that the box uses however is not measured by the system. This way the user gets an accurate measure of what the appliance in question uses. This is done by measuring the current leaving the measurement box, which is the current that goes into the appliance. The power supply consists of a variable DC power supply that was originally set to 7VDC. This 7V is then passed through a National Semiconductor voltage regulator LP2954 that will have 5V 1.2% output. The schematic of the power supply can be seen below in Figure 11.

Neutral Neutral 7V DC Supply Hot Vac 7V out IN 5V Regulator OUT Hot

Wall Plug GND 1.5 uF 1.98 uF Gnd 0 Gnd 0 Figure 11: Diagram of the 5V power supply.

Packaging Design - The overall design of the system can be seen below in Figure 12. The box will contain all the hardware and will be connected to the computer by the serial port cable. It has a cord that connects it to the wall and has a utility plug on it where the appliance can be plugged into. The prototype box measures 6x3x8” and is made of black plastic. Plastic was chosen over metal because it will not scratch appliances or the floors it is placed on, it also acts as an electric insulator, which should make the device safer. Power Cord Power Cord Prototype

Wall Socket Appliance RS232 Cable

Computer

Figure 12: Block Diagram of system.

Testing Description: - Check the capability of the system to display the correct information to the interface and store the data. This can be done with short test cases. - The A/D will be fed with a constant voltage (analog signal); the chip output will be connected to the serial port of the PC. The computer program will then poll the serial port and record the data to the hard drive. Acceptance criteria: The test is successful if the expected output is received and recorded in the data file. Since a constant voltage is being used the data file should have one numerical value repeated throughout the file. - As functions are added to the interface, check them individually. - For the final product, run a long test case bringing all the functionalities together.

Risks & Management: - Lost member: With 2 EE and 2 CPRE, if a member is lost, then the remaining EE or CPRE will need to pick up the slack of that member. Loosing two members would cause the project to fail. - Failures: Through multiple approaches we should be able to develop a working model of power consumption. - Lack of communication: There are three methods already in place that are working effectively: email, telephone, and direct communication Financial Budget

Table 2: Financial Budget Estimated Item Estimated Cost Poster $100 Equipment and Materials $100 Total $200

Table 3: Financial Budget Actual Item Actual Cost Poster $40 Equipment and Materials $100 Total $140

Personal Effort Budget

Table 4: Personal Effort Budget Estimated Team Member Estimated Effort Matthew Gordon 102 Hours Sunil Varghese 120 Hours Ying Luk 118 Hours Adam Wheeler 94 Hours

Table 5: Personal Effort Budget Revised

t t t r s s e g g h f r r r t e g g c n n i t o o o o r i i

n n s s t p p p i i a c n b o t t s e e e e a e o e e r r r e P f s i

e e r t l e T n n e W a a t a g R r M M n l i

n i g r r s p I

F e e o t t r s b c n e D i i t e

v m j u d e d o p r n A M a P m

o p n u o C i o t r a c G i r

b Revised a F

m Estimated e t

Team Members s

y Effort s Matthew Gordon 16 15 9 2 0 0 3 3 4 0 5 57 hours Sunil Varghese 17 15 6 4 0 0 3 3 4 0 4 56 hours Ying Luk 17 16 5 5 0 0 3 3 4 0 4 57 hours Adam Wheeler 17 16 11 2 0 0 4 5 5 0 4 64 hours

Total Effort 67 62 31 23 0 0 13 14 17 0 17 244 hours Project Schedule

Table 6: Gantt Chart

Sep 2002 Oct 2002 Nov 2002 Dec 2002 Jan 2003 Feb 2003 Mar 2003 Apr 2003 ID Task Name Start Finish 9/1 9/8 9/15 9/22 9/29 10/6 10/13 10/20 10/27 11/3 11/10 11/17 11/24 12/1 12/8 12/15 12/22 12/29 1/5 1/12 1/19 1/26 2/2 2/9 2/16 2/23 3/2 3/9 3/16 3/23 3/30 4/6 4/13 4/20

1 Project Definition 9/2/02 9/6/02

2 Technology Selection 9/9/02 11/19/2002

3 Project Design 11/22/02 4/4/03

4 Project Implementation 1/13/03 4/4/03

5 Project Testing 1/20/03 3/28/03

6 Basic Functions 1/20/03 2/21/03

7 Extra Functions 2/24/03 3/28/03

8 Project Revision 9/2/02 9/2/02

9 Project Documentation 9/2/02 4/25/03

10 Project Plan 9/2/02 10/8/02

11 Project Poster 10/14/02 10/22/02

12 Design Report 10/25/02 12/18/02

13 Final Report 1/13/03 4/25/03

14 Project Demonstration 4/28/03 5/2/03 Closure Material Project Team Information

Matthew Gordon Sunil Varghese 1100 Pinon Dr. #2 611 Meadow Pl. (515) 360-4345 (515) 451-9109 [email protected] [email protected] Electrical Engineering Computer Engineering

Ying Chiu Luk Adam Wheeler PO Box #9083 202 Creekside Dr. (515) 708-1202 (515) 232-0766 [email protected] [email protected] Computer Engineering Electrical and Computer Engineering

Herb Harmison James Triska 2692 Meadow Glen Rd 2218 Coover Ames , IA (515) 294-4676 Tel. # (515) 292-7059 [email protected] Faculty Advisor

Glenn Hillesland 2315 Buchanan Dr. Ames, IA Tel. # (515) 232-7661

Summary

This system has resounding possibilities. The need for energy consumption becomes greater everyday and anyway that we can help will make for a better future. This is a very attainable project that can be accomplished incrementally, which means a final product should not be a problem. The solution that has been laid out can be achieved because similar things have been done successfully. The system is just building upon those already in existence.

References smarthouse.com radioshack.com http://www.ee.ualberta.ca/~elliott/ee552/studentAppNotes/2000_w/interfacing http://www.ucfprofessor.com/ucf/eel4767/serial.html http://www.howstuffworks.com/serial-port2.htm http://www.rdrop.com/~cary/html/serialportdocs.html