2.0 Discussion: 2.1 Approach:

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2.0 Discussion: 2.1 Approach: The design for a Power Monitor and Data Logging System is comprised of two major components: the Power Meter and the Data Logger.

1 2.0 Discussion: 2.1 Approach: The design for a Power Monitor and Data Logging System is comprised of two major components: the Power Meter and the Data Logger. The Power Meter is the package that plugs into a standard household outlet, into which is plugged the appliance to be measured. The Power Meter displays power, voltage and current on the face of the device, and also has input switches. The Power Meter s internal components consist of transducers, a microcontroller, a display, and a wireless transceiver. The Data Logger is the wireless receiver unit that connects to the user s home computer. The Data Logger consists of a microcontroller, a wireless transceiver, and the software used by the home computer. Figure 2-1 provides a conceptual design of the system, while Figure 2-2 shows a functional block diagram. Figure 2-1: Conceptual Overview of System The Power Meter plugs into the wall outlet and an appliance is plugged into the Power Meter. The transducers measure voltage, current, and power and this data is temporarily stored in the microcontroller. This data is shown on the face of the device through the LCD. Various input switches on the Power Meter allow for control its operations. If the transmit switch is set to ON, the microcontroller sends the data wirelessly to the Data Logger using the wireless transceiver chip. The Data Logger receives this data through its transceiver chip. The data is then passed on to the computer software through the Data Logger microcontroller. The software gives the user access to the data and allows extensive calculations and record keeping. Page 1 of 11

Figure 2-2: Block Diagram of Power Monitor and Data Logging System 2.1.

2 Figure 2-2: Block Diagram of Power Monitor and Data Logging System User Input The input on the Power Meter consists of an On/Off switch, a Voltage/Current toggle button, a Transmit On/Off switch, and three switches which set the device identification code. These switches are labeled in Figure 2-3. Page 2 of 11

3 Figure 2-3: Power Meter user input The On/Off switch is the main power switch for the Power Meter. The Voltage/Current toggle button is a simple push button that alternates the display between voltage and current as long as the button is pressed. The Transmit On/Off switch deactivates the wireless transceiver chip. The device ID code is set using three toggle switches. This ID code is used for error checking during transmission and to allow one Data Logger system to differentiate between several Power Meters. Each of these inputs is described in more detail in the following sections Transducer / Data Manipulation The function of the transducer is to measure electrical parameters off a singlephase system. In order to obtain the necessary information required for this system, a power transducer, voltage transducer, and current transducer are used. The SINEAX I 503, U 504, and PQ 502, produced by GMC, are the three transducers used [1]. The connection diagram, Figure 2-4, shows how the units are used in the system. Figure 2-4: Connections between load and transducers The AC voltage transducer measures voltage across a source or load. This is done by first isolating the source line from the transducer by using a voltage transformer. Then the signal is sent through a RMS converter and on to the A/D converter. The AC current transducer measures current in series with a source or load. This is done by first isolating the source line from the transducer by using a current transformer. Then the signal is sent through a RMS converter and on to the A/D converter. The AC power transducer takes the product of the current, voltage, and cosine of the phase angle between the current and voltage. The resulting signal is sent to the A/D converter. The output signal that is sent from each transducer to the A/D converters on the microcontroller is a 0 to 5 V-DC signal that is proportional of the original RMS signal because the microcontroller is unable to handle a 120 volt-ac, 12 amp-ac signals. Page 3 of 11

4 2.1.3 Microcontroller The purpose of the control unit is to coordinate the memory, arithmetic and logic calculations, input, and output units. It also has to sense the states of the inputs to the device and send the correct control signals to the LCD display. The control unit has to perform the input and output operations that are implemented. The Motorola 6809 microprocessor was considered at first. To make use of the 6809, other units like a 6821 PIA (Peripheral Interface Adapter) are needed for it to interface with the outside world. The decision was made to go with a microcontroller because it encompasses RAM, ROM, and a microprocessor all in one unit. A microcontroller packaged by XEMICS was selected as the control unit for the Power Meter and the Data Logger. The XE88LC01 microcontroller comes from the family of XE88LC00 microcontrollers [2]. The key features of the microcontroller are listed in Table 2-1 and a functional block diagram is given in Figure 2-5. The cost of this microcontroller is $8.00 per unit if 10,000+ units are purchased. Table 2-1: Key Features of XE88LC01 Microcontroller -Ultra low-power (300 microa at V) -512 Bytes of RAM -Low-voltage operation (2.4 V supply voltage minimum) -Complete development tools using Windows95 or NT graphical interface -4 x 2 or 7 x 1 PGA-ADC input multiplexer -Assembler -ANSI-C compiler -Current and memory usage monitoring -CPU Simulator Page 4 of 11

Figure 2-5: Microcontroller Functional Block Diagram The XE88LC01 has sufficient peripherals for use as the control unit for both the Power Meter and the Data Logger.

5 Figure 2-5: Microcontroller Functional Block Diagram The XE88LC01 has sufficient peripherals for use as the control unit for both the Power Meter and the Data Logger. The Zooming ADC is an analog to digital converter that can convert any of 8 selected inputs into digital data. This feature is connected to the 3 transducers used to measure voltage, current, and power. The XE88LC01 also has a Universal Asynchronous Receiver Transmitter (UART) and a Universal Synchronous Receiver Transmitter (USRT). Both of these sub-blocks are used to control the XE1201A transceiver chip. The USRT handles the 3-wire control bus for the chip, while the UART controls the flow of actual data to and from the transceiver. Multiple digital input/output pins are used to interface with the display driver and the external input switches. The display driver is described in the next section. In the Power Meter, the XE88LC01 is interfaced with the transducers, the input switches, the LCD display, and the transceiver. The microcontroller receives analog inputs from the voltage/current/power transducers, and multiplexes them into digital data. The microcontroller then checks the value on the toggle switch and sends the correct data to the LCD s built-in display driver, the HD44870, to be displayed. The microcontroller outputs the data to the transceiver via the 3-wire serial bus. The microcontroller transmits this data to the transceiver using the UART and the USRT. Page 5 of 11

4 Display To display power, current, and voltage to the user, a Liquid Crystal Display (LCD) unit is connected to the Power Meter microcontroller.

6 The XE88LC01 is also used as the controller within the Data Logger. It controls the operation of the transceiver, does the necessary protocol calculations, stores all the data received, and handles uploading the data to the computer Display To display power, current, and voltage to the user, a Liquid Crystal Display (LCD) unit is connected to the Power Meter microcontroller. The SC0802B display is used with the HD44870 display driver to display two banks of 8 digits [3]. Each digit is a 5x7 dot matrix and is capable of displaying any alphanumeric character. The top bank always displays power and the bottom bank displays voltage or current, depending on user input. The layout of the display is shown in Figure 2-6. Figure 2-6: SC0802B LCD display format Wireless Communication The purpose of the wireless communication is to transmit the current, voltage, and power data from the Power Meter to the Data Logger as shown in Figure 2-7. The main wireless component is the wireless transceiver chip, which requires some external circuitry and an antenna. A transceiver is a combination of transmitter and receiver. Two transceivers are used to allow two-way communication to set up data transfers. This ability to set up transfers allows one Data Logger to handle multiple Power Meters throughout the house. Figure 2-7: Interfacing between transceivers, microcontroller and computer Page 6 of 11

7 Several key features are desired in the transceiver component. Easy interface with a microcontroller is one requirement. Fast transmission is also necessary so that data can be sent without interrupting the sampling rate of new data. The chip must also have extensive documentation for easy implementation into the overall design. A final feature is that it must be small enough to fit into a small package. After extensive research, the XE-1201A Low-Power Ultra High Frequency (UHF) transceiver chip, produced by XEMICS, was selected [4]. This transceiver was chosen since it has all the desired features. The transceiver is a small 32-pin chip (7 x 7 x 1.2 mm). A 3-wire bus is used for interfacing with a microcontroller, as seen in Figure 2-7. The data rate peaks at 64 kbit/s. It operates in the Mhz frequency range and has an indoor range of 30 to 70 meters. Few external components (capacitors, resistors, an antenna) are needed in addition to the actual chip. The extensive online documentation, including sample configurations, makes the chip easy to configure and use. Table 2-2 lists key features of the XE1201A. Table 2-2: Key Features of XE 1201A -Small chip, 32 pin-package -Very low power (2.4 V supply voltage) -Half-duplex operation -3-wire bus for easy Micro-controller interface -Output power programmable via bus -Few external components (antenna, matching network, tank circuits, saw resonator for local oscillator and low cost crystal) -Data rate up to 64 kbit/s Hz operation frequency m range (applicable for home use) A key feature of the wireless communication protocol is the ID code for each Power Meter. The purpose of this ID code is to identify and distinguish between each of the Power Meters used. This ID code allows multiple transceivers transmitting data to one base station. This ability is demonstrated in Figure 2-8. Page 7 of 11

8 Figure 2-8: Multiple Power Meter, single Data Logger setup The three switches on the Power Meter, as seen in Figure 2-9, set the ID code. The Transmit On/Off switch is used to disable the wireless transceiver. This allows the user to save power when not collecting data from the Power Meter. Disabling wireless transmission also prevents multiple wireless signals from interfering with each other. Enabling only the Power Meter that the user wishes to log from ensures a clean signal. Figure 2-9: Power Meter input used for In the 2-way communication conducted in PMDLS, the transceiver in the Power Meter side, which is ready to transmit data, sends a ready to send signal to the transceiver in the Data Logger. This signal also includes the ID code of the Power Meter sending the request. Upon receiving this request, the Data Logger responds with a ready to receive signal containing the same ID code. All the Power Meters with transmission enabled pick up the signal and check the ID code. Only the Power Meter whose ID code matches the one in the ready to receive signal will begin transmitting data Software The function of the software is to make it easy for the user to log data and to allow extensive analysis of the data. The software is written in Visual Basic and the finished program is a stand-alone executable file. The program consists of two main components, the Virtual Home Utility and the Power Meter Logger Utility. The Virtual Home Utility is a file manager that makes it easy for the user to list all the appliances in their home, walks them through the process of logging data for each appliance, and then allows analysis and display of their total energy usage. Figure 2-10 shows a preliminary layout of the main Virtual Home window. Page 8 of 11

9 Figure 2-10: Virtual Home Utility main window In the main window, the user defines the rooms of their house. For each room, the user can select and add different appliances by dragging an icon to the white box, adding a description, and clicking the Add Item box. All the appliances for a room are listed, and whether or not any data has been logged is also shown. Once data has been logged for each listed appliance, the software can estimate the total energy consumption of all appliances in the home. The utility can also analyze how the total energy usage is distributed between the appliances and make suggestions on how to reduce overall consumption. The Power Meter Logger Utility controls the actual logging sessions that receive data from the Power Meter. A preliminary layout for this utility is shown in Figure After selecting a room, the user can select which appliance they wish to log data for. The appliance list is split into appliances with previous data and appliances with no data. Once the appliance is selected, other parameters, like sampling rate, can be specified. The toggle switches that set the ID code are used to verify that the incoming data is coming from the correct Power Meter. Page 9 of 11

Figure 2-11: Power Meter Logger Utility main window Once data has been logged using the main window, the data files can be opened in a spreadsheet, where calculations and graphing can be done. 4.

10 Figure 2-11: Power Meter Logger Utility main window Once data has been logged using the main window, the data files can be opened in a spreadsheet, where calculations and graphing can be done. 4.0 Cost 4.1 Fiscal Fiscal costs hardware costs, labor, and other development costs. Hardware costs include the actual microcontroller and transceiver chips, transducers, and other required circuit components. The hardware costs are enumerated in Table 4-1. A summary of all cost estimates is given in Table 4-2. According to the project timeline, the total project length would be 10 weeks. 200 work hours are assumed for this period. Assuming that the hourly labor cost for an engineer is $60, the total manpower cost is $12, Other development costs include the programmer board required to program the XE88LC01 microcontroller, and a software development kit. For writing Visual Basic code, Microsoft Basic 6.0 is used, which costs $549. Page 10 of 11

11 Table 4-1: Hardware Cost Estimates Power Monitor and Data Logging System Brand Description Model # Quantity Price/PartQuantity GMC AC current/voltage Transducer SINEAX I 503 / U 504 $ $60.00 GMC Power Transducer SINEAX PQ 502 $ $30.00 XEMICS Microcontroller XE88LC01 10K+ $ $13.06 XEMICS Wireless RF IC XE K+ $ $11.20 DME LCD Unit (with Driver) SC0802B $ $10.00 Shin Red Button R13-24BL $ $1.29 Radio ShackRocker Switch $ $1.49 Switronic Slide Switch 601S1M1 $ $5.96 Belden 16AWG Ground Wire Per foot $ $1.90 Radio ShackAntenna N/A $ $10.00 Radio ShackOther (Resistors, Capacitors, etc)n/a $ $10.00 N/A Unit Enclosure N/A $ $5.00 Total $ Table 4-2: Total Cost Estimate Hardware (per unit) $160 Labor (200 hrs at $60/hr) $12,000 Programmer Board for microcontroller $300 Software Development Kit (Visual Basic 6.0) $549 Total Estimated Cost $13, List of References 1. downloaded 5/4/ downloaded 4/9/ ftp://ftp.dmetechnologies.com/pdf/sc0802a.pdf, downloaded 5/7/ downloaded 4/9/ Page 11 of 11

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