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2.0 Discussion 2.1 System Design

Group xyz’s solution for the power monitor and data logging system is a microprocessor-based device. When plugged into a standard 120-volt wall socket, the voltage and current is transformed to an appropriate level and is fed through an analog to digital converter (ADC). This data is then sent to the microprocessor, which handles user input as well as output to the liquid crystal display (LCD) and the communications device. The communications device has the capability to transmit the voltage, current and power readings to a personal computer. As shown in Figure 2.1, the primary components of the system are the packaging, ADC, microprocessor, display, communications, and the PC software.

Figure 2.1- Functional Block Diagram of the Power Monitor and Data Logging System

2.1.1 Packaging

The enclosure is the M 57 23 214 from OKW Enclosures Corporation. This package was selected for several reasons. First, the package is in the specific size range desired. The package has the dimensions of: 120 mm in height, 230 mm in width, and 193 mm in depth. A schematic of the enclosure is shown in Appendix A. The M 57 23 214 package is shown in Figure 2.2. All the components were examined, and the size of the package is able to integrate all of them into it. The component of largest size to implement with the package is the LCD display, LM044L from Hitachi. The LCD display is 60 mm in height, which easily fits in the front panel of the M 57 23 214 with a height of 120 mm. The positioning of the LCD display is shown in Figure 2.3. All other parts, such as the printed circuit board containing all of the Integrated Circuits (IC) and other components, the infrared transmitter, the power cord, and outlet, easily fit into the inside of the enclosure. In addition to the LCD display, the placement of the IR transmitter is shown in Figure 2.3.

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Figure 2.2 - The OKW Mettec Enclosure

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[1] Figure 2.3 - Packaging Front Panel Dimensions with Liquid Crystal Display, User

Interface, and Infrared Port [1, 6, 9] Units in mm

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Secondly, the package meets the shielding needs for the design. As stipulated by the Federal Communication Committee (FCC), electrical devices should not emit an interference radiation from the unit above a certain level at a given distance. The setups of the FCC shielding tests are shown in Appendix A. In homes, offices, businesses, and for retail trade, the allowable emitted interference is 30 dB in a 30-meter distance in the range of 30 to 230 MHz. As shown in Figure 2.5, an internal source produces a given amount of interference. The amount of interference that passes through the outer wall of the enclosure should be minimized. Thus, the enclosure needs to attenuate any interference that is being radiated internally from the device. Also, the electrical device needs to function when placed into an existing electromagnetic field. As shown in Figure 2.4, a given amount of interference energy is radiated at the enclosure. The shielding wall of the enclosure needs to reflect the interference energy away from the internal circuitry. When the interference energy is transmitted through the outside of the shielding wall, some of the energy is then transmitted through the inside shielding wall and the rest of the energy is reflected back to the outside wall. This reflected energy can then be reflected off the outside wall and transmitted through the inside face, which causes the lower arrow in the Figure 2.4. The amount of energy transmitted through the inside wall of the enclosure needs to be kept to a minimum. The M 57 23 214 enclosure meets and exceeds the shielding standards set forth in FCC Docket #20780, Part 15, Subpart J. In Appendix A, attenuation performance and penetrated radiation from OKW Enclosures Corporation are given on their product.

Figure 2.4 – Electromagnetic Shielding [1]

Figure 2.5 – Electromagnetic Interference [1]

Lastly, the OKW enclosure is the most cost effective choice of all other packages researched. The

custom packages costs were in the range of $600-$800. The M 57 23 214 costs just $103. There were less expensive packages made of plastic available from OKW Enclosures Corporation. Because plastic is not durable, susceptible to cracking and breaking, which would expose all internal circuitry, a metal package was chosen. Thus, the M 57 23 214 package meets all desired expectations and is the most inexpensive solution for the design.

Other components selected associated with packaging were the AC line cord and receptacle. The AC line cord chosen is the 311024-01 from Qualtek Electronics Corporation. It is six feet seven inches in length. The cord has a rating of 15 amps at 125 volts. The AC receptacle, 710W-00/01, was also selected from Qualtek Electronics. The receptacle has a mounting plate for easy assembly to the wall of the packaging. It is accessible for both two prong and three prong AC line cords. The AC line receptacle and cord are shown in Figures 2.6 and 2.7. Information for both products is provided in Appendix A.

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Figure 2.6 - Qualtek AC Receptacle [3] Figure 2.7 - Qualtek AC line cord [3]

Figure 2.8 – Power Flow Diagram with Power Transformation and Current Sense

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2.1.2 Attenuation Circuitry The power-monitoring unit is plugged into a standard 120-volt wall outlet. It is desired to measure how much voltage and current an appliance, which is plugged into the monitoring unit, is being supplied. Thus, a reference has to be taken off the power line and examined. This reference can be at a maximum 120 volts and 15 amps. Since the signal to the analog-to-digital converter and the microprocessor has to be in the range of 5 volts, attenuation of the reference signal must be done. A figure of the overall flow of this function is provided in Figure 2.8.

In order to measure current, a signal must be sent to the analog-to-digital converter as a voltage that is proportional to the amount of current received. MagneTek’s CSE187-L, a low frequency current sense, is used to send a proportional DC voltage signal to the analog-to-digital converter. The CSE187-L is shown in Figure 2.9. The device is printed circuit board (PCB) mountable, and withstands an input current of 30 amps, which far exceeds the design parameter of 20 amps. The scaling factor of the current sense is 110 mV/amp. The low frequency current sense is an economical solution at $2.89. More information about MagneTek’s CSE187-L low frequency current sense is provided in Appendix B.

Figure 2.9 – MagneTek Current Sense [3] The voltage of the line is far too high at 120 volts to be sent to an analog-to-digital converter, so

the use of a step-down transformer is needed. The SPK0030400-10000 was chosen from Advanced Components Industries Incorporated. In Figure 2.10, a picture of the step down, SPK0030400-10000, voltage transformer is given. It is printed circuit board mountable, so that all electronics can be kept on one circuit board inside the enclosure. It has a secondary RMS rating of 4 volts at full-scale input with the primary voltage being 120 volts. The secondary RMS voltage signal of 4 volts is sent to the analog-to-digital converter. The analog-to-digital converter, ADS1240 from Texas Instruments, can easily be supplied with 4 volts, which corresponds to full voltage input. The scaling factor is then 0.03333Vout/Vin. This allows a voltage to be sent to the analog-to-digital converter that is proportional to the input voltage of the monitor. The transformer is reasonably priced at $12.78. More information about the SPK0030400-10000 is given in Appendix B.

Figure 2.10 – Power Transformer from Advanced Components [2]

2.1.3 Analog to Digital Conversion:

From the wall outlet to the appliance, two analog signals are of concern, the voltage and the current. After the voltage and the current have been measured, the voltage signal is scaled down through a transformer. As of this point our signals are in analog form. Before these signals go to the microprocessor to be processed, the signals need to be converted from analog signals to digital signals.

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The proposed solution is to use an analog to digital converter to digitize the signal conditioned voltage and current signals. The ADS1240 is capable of performing this conversion with adequate resolution and speed. The parameters for the ADS1240 are shown in Table 2.1. The ADS1240 is shown in Figure 2.11.

Table 2.1 - Parameters for ADS1240 ADC [3] Parameter Name Value

Resolution (Bits) 24 Sample Rate 0.015 (ksps) Supply (V) 3 to 5 Analog Inputs 4 Power (typ) (mW) 0.6 DNL (max) (+/-LSB) 1 INL (max) (+/-LSB) 256 Data-Bus Interface (bits) Serial Cost $3.60

The ADS1240 A/D interfaces easily to the Zilog Z80 microprocessor. The ADS1240 uses serial

data transmission. The interface is accomplished using a Z80 SIO. The SIO can be interfaced to the microprocessor as shown in the Serial Interface section and in Figure 2.19. The microprocessor controls the Reset and Chip Select lines to reset and select the ADS1240. The A/D interface to the SIO is shown in Figure 2.12.

Figure 2.11 – The ADS1240 Analog to Digital Converter [5] The ADS1240 has acceptable resolution and its power consumption is relatively low. It is capable

of handling all of our analog inputs and is a cost effective solution at $3.80. One disadvantage of the ADS1240 is that its sample rate is relatively low, but for measuring the sinusoidal signals of current and voltage, the sample rate of the ADS1240 is sufficient because the average values are determined by the microprocessor. Additional information on this component is found in Appendix

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C. Figure 2.12 - ADS1240 Interface to Microprocessor via SIO [4,12] 2.1.4 Microprocessor

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In order to calculate power from the ADC readings, a 16-bit Zilog Z80 microprocessor is selected to perform such a task. Figure 2.13 shows the Z80. This processor has a simple instruction set, which is easy to develop. In addition, the part is cost effective at $1.57 per unit. The microprocessor takes the current and voltage values and relays this information to the LCD, as well as to the communications device. The microprocessor also has to handle user commands on the front panel, which is accomplished using interrupts. As the microprocessor reads voltage, current, and calculates power data, it stores the data in random access memory (RAM), where the data is constantly refreshed. The assembly program for the microprocessor is stored in the read only memory (ROM), while the microprocessor receives and outputs signals via a parallel input/output controller (PIO). Also, the microprocessor averages several readings to make sure the data is accurate before sending the information to the display and the communications device.

Figure 2.13 – Zilog Z80 Microprocessor [6] The Zilog Z80 microprocessor that is used, namely the Z08400, has a 16-bit address bus and is

interfaced to the serial input/output controller (SIO) device from the ADC. Since the selected ADC sends the current and voltage in serial, the SIO converts the data into parallel so that the address bus can process the information. The RAM used to store the current, voltage and power as the data is being processed is the Toshiba TC551001CF-70L-ND, which is a 128K x 8 IC SRAM. The ROM that is used to store the assembly program for the microprocessor is the Toshiba AT27C256R-70JC-ND, which is a 32K x 8 CMOS EPROM. The PIO that is selected for the input and output signals is the Zilog PIO Z84C21010FEC. The following program flow diagram for the microprocessor is shown in Figure 2.14. Before the microprocessor can receive current and voltage, it has to first be initialized. The input and output of the microprocessor is determined by setting the PIO so that the microprocessor can receive the current and voltage from the ADC via the SIO. The variables used in the assembly program are also initialized in order to store readings and the calculated values that the microprocessor performs. When the initialization tasks are completed, the microprocessor is ready to read the current and voltage values from the ADC. The current and voltage readings from the ADC are stored in two different variables. The microprocessor continues adding continuous readings for a certain amount of the time and then takes the average of each variable. After the average values of current and voltage are acquired, the current and voltage are multiplied to obtain power since P=IV, where P is power, I is current and V is voltage. After storing these values, the microprocessor checks for user input to determine what it should display and sends this information to the communications device. The program then loops back to where the variables are initialized and the whole process repeats itself. Further information about the microprocessor is found in Appendix D.

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Figure 2.14 - Flow Diagram for Microprocessor Assembly Code

2.1.5 Display

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The Hitachi LM0447L Liquid Crystal Display (LCD) module is Group xyz’s choice to implement the display functionality of the power monitoring system. The LM0447L is shown in Figure 2.15. This LCD module is best suited for this project because of its large screen area (4 lines of 20 characters) and low cost ($8.28). The dimensions of the LCD module are shown in Figure 2.3. The LCD module is mounted to the front panel of the power monitoring system. It has a built in controller, the Hitachi HD44780, which easily interfaces to the Zilog Z80 as shown below in Figure 2.16.

Figure 2.15 – Hitachi LM0447 LCD Display [7]

Figure 2.16 - LCD Interface to the Microprocessor via a Parallel Controller

The LM0447L LCD module easily interfaces to the Z80 processor through the Z80 Parallel Input Output controller (PIO). To power the LCD module, the VSS and Vo inputs are tied to ground and the VDD input should be tied to +5 V. Figure 2.16 shows a connection diagram. The Vo input is the base voltage level. In this application it is easiest to tie the base voltage to ground so that the base voltage is zero providing a convenient reference point. The VSS input is used to set the amount of back lighting displayed on the LCD. The back lighting option is not used in this design, so this input is also tied to ground. The VDD input is the supply voltage. This LCD module requires +5 V DC to operate, so the VDD input is tied to the +5 V power supply.

The connections for controlling the LCD module are also shown in Figure 2.16. In this application, the microprocessor is only writing data to the LCD. The read/write line (R/W) is tied to ground so that the microprocessor is always writing data to the LCD module. The Enable input (EN) is connected to data bit 1 (DB1) of the PIO. The microprocessor controls whether the LCD is enabled or not enabled by writing a logic one to DB1 or a logic 0 to DB1 respectively. Data bit 0 (DB0) of the PIO is connected to the RS input on the LCD module as shown above in Figure 2.16. This allows the Z80 to select whether the data written to the module is instruction code input (RS = logic 0) or data input (RS = logic 1). Data bits 7 through 4 on the LCD module are connected to data bits 7 through 4 on the PIO. A total of 8 bits are needed by the LCD module to form a data input or an instruction code. In this

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configuration, the LCD is operating in four-bit mode. The microprocessor first sends the four high order bits of the instruction or data. After the LCD module has received the four high order bits of the instruction or data, the microprocessor sends the low order four bits of the instruction or data. The LCD module then has all eight bits of the instruction or data. Using the four-bit mode of the LCD module is advantageous because it allows the microprocessor to control the LCD and send data/instructions to the LCD using only one eight-bit PIO. Further information about the LCD module is found in Appendix E. The LCD provides the backbone for the user interface.

2.1.6 Menu Driven Interface The user selects which value to display on the LCD via a menu driven interface. This interface consists of the LCD display and 4 input buttons (select, return, right-arrow, and left arrow) as shown in Figure 2.3. The LCD screen initially displays “POWER”. If the user wishes to see the measured power value, they press the select key. Once the user is done viewing the measurement, they press the return key to return to the menu. If a user wishes to see a different parameter, they would press the right-arrow key. Pressing the right-arrow key displays “VOLTAGE”. This menu is cyclic, after the user has scrolled through “POWER”, “VOLTAGE” and “CURRENT”, another right-arrow key press displays “POWER” again. Pressing the left-arrow key moves the menu back to the previous parameter. The buttons to implement this menu are momentary switches connected to the Z80 microprocessor via a Parallel Input Output Controller (PIO) as shown in Figure 2.17. Any pressed button interrupts the microprocessor. Data bit 0 (DB) on the PIO is connected to the select button, DB1 is connected to the return button, DB2 is connected to the right-arrow button and DB3 is connected to the left-arrow button. The microprocessor reads in an eight-bit value and discards the unused bits. It then uses the remaining bits to determine which key was pressed and then displays the appropriate response on the LCD.

Figure 2.17 - Switch Interface for Menu Driven System [6,7,8] 2.1.7 Communications The Actisys IR100Si Infrared (IR) transceiver is Group xyz’s choice to implement the communications functionality of the power monitoring system. This IR transceiver is best suited for this application because it easily interfaces to the Z80 microprocessor through a serial connection. Two Actisys IR100Si’s need to be purchased if the remote PC does not have an existing IR port. The IR100Si is shown in Figure 2.18.

The IR transceiver has infrared communication speeds of up to 115.2 kbps. The IR 100Si has built in hardware and software that converts serial data so that it can be transmitted via IR communications. This conversion works in reverse when the IR 100Si receives data from a remote source. The IR data is converted into serial data so that the microprocessor can use it. The IR 100 Si is fully compatible with the IrDA-1.0 protocol specifications, enabling it to communicate with many IrDA compatible handheld

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devices, such as cellular phones and personal digital assistants (PDA). This IR module also has built in flow control to minimize the corruption of the IR data during transmission. The Actisys IR100Si can easily interface to the microprocessor via a RS-232 serial connection. Figure 2.19 depicts the microprocessor to IR module interface. The serial connection provides power to the Acitsys IR100Si through pin 9 of a DB9F connector configuration. The DB9 connector provides an interface so that serial data can be sent to the Actisys IR100Si. The DB9 connection is shown in Figure 2.20.

Figure 2.18 – Actisys IR100Si IR transceiver [10]

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Figure 2.19 - IR100 Si Interface to Microprocessor via SIO [created from 10,11,12,13,14]

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Figure 2.20 - DB9 RS-232 Connector and Pinout Diagram [14] In Figure 2.20 the Data Set Ready pin and Ring Indicator pins of the DB9 connector are connected

to an RS-232 high voltage. In this application, the power monitor always sends data at the end of every microprocessor code cycle while the monitor is receiving power. The Data Set Ready pin can be connected to a high RS-232 voltage because the monitor is ready for data while the power is on. The Ring Indicator pin is not used by the IR 100 Si for communication control. This pin is tied to a high RS-232 voltage to power the IR 100 Si.

For the remaining connections, the DB9 connector is connected to the Maxim MAX223 RS-232 driver. The MAX223 takes in transistor-transistor logic (TTL) voltage level inputs (0 to +5 V) and outputs RS-232 voltage levels (0 to +15 V). This allows serial data from the Z80 Serial Input Output controller (SIO) to be transformed into voltage levels acceptable for RS-232 communications. The SIO to microprocessor interface is shown in Figure 2.19 and is described in the Serial Interface section. Further information about the IR module is found in Appendix F. Further information about the RS-232 driver is found in Appendix F. 2.1.8 Serial Interface

The SIO receives serial data through the RxDA line and transmits serial data through the TxDA line as shown in Figure 2.19. The RxCA and TxCA lines are driven by a clock (CLK) which is generated by a Z80 Counter Timer Circuit (CTC). This controls when the data (transmit or receive) data is sampled. The interrupt lines and control lines are connected to the to the corresponding lines on the microprocessor. The SIO is then interfaced to the Z80 microprocessor as shown in Figure 2.19. The parallel data (DB7 through DB0) from the microprocessor is converted to serial data in the SIO. Data can be sent to and from the microprocessor using the SIO. The microprocessor then controls the data transmission and sends and receives data using the single SIO. Further information on the SIO can be found in Appendix F. 2.1.9 PC Software

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Group xyz chose Visual Basic in order to implement our PC software. Our program displays the voltage, current, and power, in real-time, upon user request. Once the user starts the readings sequence, the PC receives the voltage, current, and power readings from the power monitor at regular intervals. This data can be stored and written out to a standard text file, which can then be examined and further manipulated in a spreadsheet program, such as Microsoft Excel. As shown in Figure 2.21, the user interface is simple and intuitive. It allows one kind of reading to be seen on-screen at any given time, exactly like the front-panel display of the power monitor.

Figure 2.21 - Power Monitor Main GUI

Additionally, the software has the capability to accept user-defined limits. The user can set upper

and lower bounds for any combination of voltage, current, and power, and be informed, via the main form, when these limits are exceeded. This feature is useful if the user wants to make sure that the device being monitored does not exceed any upper or lower bounds in voltage, current, or power. Although not in the original specification, the simple nature of Visual Basic allows this extra feature to be implemented with virtually no additional overhead. The form used for this purpose is shown in Figure 2.22. The code which implements the limit testing is found in Appendix G.

Figure 2.22 - Power Monitor Watchdog GUI

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4.0 Costs 4.1 Fiscal

The cost of Group xyz’s proposal is summarized in Table 4.1. This includes the selected components for packaging, analog-to-digital conversion, the microprocessor, the display, and the communications port.

Table 4.1- Power Monitor and Data Logging System Costs Part Model Cost

Packaging OKW M5723214 $103.00 Power Transformer SPK0030400-10000 $12.78 Current Sense MagneTek CSE187-L $2.89 ADC TI ASD41240 $3.80 Microprocessor Zilog Z80 $1.57 PIO Controller Zilog Z84C2010FEC $2.62 SIO Controller (2) Zilog Z8023010PSC 2 x $16.82 RS-232 Driver Maxim MAX223 $7.55

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Counter Timer Circuit Zilog Z84C3010PEC $5.10 Display Hitachi LM044L $8.28 Communication Actisys IR 100 Si $350.00 Buttons/Connectors/etc. $10.70

Total Parts Cost: $541.93 Total Parts and Labor Cost: $4810.93

The consulting fee for each engineer in Group xyz is $60 per hour. The total consulting cost is

approximately $4260 for 71 hours of engineering consulting. Group xyz feels that $541.93 is a reasonable price for the power monitoring unit considering the features mentioned above. Given the information the power monitor supplies, the consumer can save a considerable amount of money. 4.2 Time The time distribution for this design is depicted in Figure 4.1. As is shown, work on each section of the project continued throughout the design period.

Figure 4.1 – Timeline Describing Task Distribution Over Time

6.0 References Packaging 1. http://www.okwenclosures.com/catalogue/metal/info_pages/mettecdeskinfo.htm 2. http://www.advancedcomponents.com

Weeks

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3. http://www.digikey.com ADC 4. http://focus.ti.com/docs/prod/productfolder.jhtml?genericPartNumber=ADS1240 5. http://www-s.ti.com/sc/psheets/sbas173/sbas173.pdf Microprocessor 6. http://ebiz.zilog.com/products/partdetails.asp?=id=Z08400 Display 7. http://www.farnell.com/datasheets/7608.pdf 8. http://www.phanderson.com/printer/lcd.html 9. http://www.zilog.com/docs/z80/z80cpu_um.pdf Communications 10. http://www.actisys.com/instantir.html 11. http://www.actisys.com/faq100s.html 12. http://pdfserv.maxim-ic.com/arpdf/1798.pdf 13. Z80 SIO datasheets via email from Zilog Technical Support 14. http://www.arcelect.com/rs232.htm PC Software 15. http://msdn.microsoft.com/vbasic/ Appendix Part A http://www.okwenclosures.com Part A http://www.digikey.com Part B http://www.advancedcomponents.com Part B http://www.digikey.com Part C http://www.ti.com Part D http://www.zilog.com Part E http://www.farnell.com Part F http://www.actisys.com Part F http://www.maxim-ic.com Part F refer to reference 13 Part G PC software code