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Date: 12/8/2010Author: Ben AveryTo:Professor MortonSubject: Automated Near Field EMI System DescriptionINTRODUCTIONThis project is an apparatus to be used in industry to take measurementsof near field Electro-Magnetic Interference. It will use a stepper motorcontrolled table to move the piece of equipment to be measured in the X and Yplane. The table is contained within an electro magnetically shielded chamber.A spectrum analyzer is kept outside of the chamber with a probe extendinginside to measure the emissions from the DUT. The spectrum analyzer and thetable are both controlled by the same Python program on the computer,outputting a CSV file of the frequency each measurement is taken at followedby its intensity in dBm that can be imported directly into Excel for analysis.DESCRIPTIONThe project has two main components, the moving table and thespectrum analyzer that are tied together by the software run by the computer.1

parts have support for receiving UART commands, the protocol for whichrequires 1 digital block. Stepper motor controls only require one bit fordirection of steps being taken and one bit for the actual step signal, so for atwo axis machine only 4 bits of information are needed to move the two motorsat any given time. Additional signals are needed for sleep mode, enable, reset,and step size (2 bit). If any of those 5 signals is changed for one steppermotor, logically the other will require the same signal, so both motorcontrollers can be driven by port. Four more bits in the ports can be used foroptional fault detection, when the user attempts to move the table beyond itslimits, though transmitting any detected faults will require a second digitalblock for UART’s Tx mode. In total, the project will require two 8 bit ports,which all PSoCs have available.The internal PSoC architecture will require an 8 bit pulse width modulatorto send the proper duty signal pulses to the stepper motor controller.Preliminary testing shows that a 2-3% duty cycle with a 25kHz signal is beingsent to the controller. The PWM can used to divide down the 24MHz frequencynative to the PSoC to the 25kHz signal. A counter is used to track how far thetable has traveled. The signals translate to approximately 1500 pulses per mm,so a 24bit counter will allow for over 11 meters of travel, plenty for mypurposes. A 16 bit counter will allow for 4 cm of travel, which is plenty formeasuring purposes, but not enough for clearance when replacing the DUT.An 8 bit PWM is 1 digital block, a 24 bit counter is 3 digital block, so the X andY axis will require 4 digital blocks each, as well as an additional 2 blocks for theUART module. Many PSoCs contain 3 rows of 4 digital blocks.The spectrum analyzer is a relatively straight forward system, commands aresent back and forth from the computer through the RS-232 or GPIB interface,and EMI tones are received by the probe from the DUT.Software:Currently, only desktop PCs with an LPT port that has had its BIOSsettings set to EPP mode can run tests on EMI using the available equipment.This is not an optimal solution for engineers that mostly use their individual3

laptops for testing and data analysis. One of the aims of the project is to havethe setup be usable by as many different computers as possible, since thecurrent EMI setup have very strict guidelines on what hardware and softwarecan be used. The preexisting setup requires LabView which, though verypowerful, is prohibitively expensive and somewhat of a “closed box system.”Since copies of the software are so expensive, there are few copies available tobe used to create and edit the program used to take EMI data, causing theprograms to be very rigid. Stellar LabView programmers are also difficult tocome by since most engineers don’t get an opportunity to use the software andbecome familiar with it. It also generates SCPI language programs through aGUI interface, which doesn’t allow the person generating the program muchinsight as to exactly what’s going on in the program at any given point. Forthese reasons I have decided to program the project in Python, using the PyVisalibrary as well as tkinter to develop a user-friendly GUI. With these two librariesI can generate a visually and functionally equivalent program to the currentLabView offering with much tighter control over the commands being sent toand received from the spectrum analyzer.Python will also be able to take control of the stepper motor controls thatare currently being handled by the EPP port and some proprietary softwareoriginally designed to control CNC setups. Control will be exerted through aconnection to a PSoC board that will output 5V signals to a printer cable,emulating the output that would normally come from an EPP portThe PSoC software will block on receiving commands from the PC thoughits UART interface. It will then decode the commands sent into 3 pieces ofinformation: axis (X or Y), direction (positive or negative), and distance. Theaxis will let the software know which PWM-Counter pair to address. Thedirection will flip the directional bit being sent to the stepper motor controllerappropriately. The distance will be converted from millimeters to step pulsesgenerated by the PWM, then loaded into the 24 bit counter before the 8 bit PWMis enabled. When the counter reaches its terminal count, an interrupt willoccur, stopping the PWM. Each of the limit switches will be tied to a GPIO(general purpose input/output) interrupt. The interrupt will stop all PWMs andCounters and send an error message back through the UART interface to thePython control program alerting the user that the error has occurred and whichswitch was tripped.User Interface:The user interface will be primarily the computer that is running all of thesoftware. A GUI will be built in Python that the user will be able to use to definethe probe movement pattern. It will also be able to set the parameters for thespectrum analyzer, such as start frequency, end frequency, sample time,number of samples taken and average versus max hold mode. The GUI will alsodisplay a preview of the measurements being taken so that the user will knowthat the data is being taken properly, avoiding problems like unpowered DUTsor incorrect spectrum analyzer settings.4

The user will need to be able to secure the DUT in the chamber to thetable. This is done with a simple clamp, oriented mostly by eye. The probe willneed to be set a known distance from the top of the chip. This will be doneusing a very precise shim to gauge the distance, as measurements being takenare extremely small, and near field EMI amplitudes roll off at a rate ofsomewhere between the inverse of the square of the distance from probe todevice to the inverse of the fourth power of the distance. The GUI will allow formanual moving of the table so that the alignment of the chip can be inspectedat all four corners of the chip.Communication Protocols:Communication will be done through two standardized protocols,Standard Commands for Programmable Instruments (SCPI) and UniversalAsynchronous Receive and Transmit (UART). SCPI will be used to communicatewith the spectrum analyzer, allowing for a wide multitude of spectrumanalyzers to be used with the same program with minimal alterations, as theprotocol is mostly universal. UART will be used to communicate with the PSoCdevice, which will then translate the signals into pulses/signals on the lines tothe stepper motor controller.5

DEVELOPMENT PLAN:Finish and prove PSoC to LPT CableWrite PSoC Table controller (UART)Build Faraday CageAssemble TableWrite Table Movement GUISpectrum Analyzer GUIHardware Design ReviewJoin GUIs togetherSoftware System PresentationCode ReviewFinal Presentations24‐Dec7‐Jan14‐Jan28‐Jan11‐Feb25‐Mar20‐Apr29‐Apr4‐May25‐May3‐JuneThe wire mesh for the faraday cage may be difficult to source; purchasingit will need to be done early on to make sure that it is received early enough tobuild the Faraday cage. The XY positioning table is also a specialty part, butthe source of the tables is known and their lead time is very short. A near fieldEMI probe will need to be found; they are prohibitively expensive. However, afunctional setup with all parts exist, all parts that need to be sourced are fordemonstration purposes only.Software development will be done in PSoC Designer for the PSoCfirmware and Notepad++ for all Python GUI work. The EMI setup shouldn’t takeup more than a desktop as the cage will be 2’x2’x2’, and the rest of the setup’sfootprint won’t be me more than 4 square feet. The majority of the softwaredevelopment will be done at Cypress semiconductor, as their system will befunctionally identical.The majority of the demonstration setup will be built off campus at aprivate shop. The faraday cage will be made out of wire mesh and wood andglued together to avoid any metal protrusions into the cage that could carryinterference. The table will be assembled with regular fasteners. Again, thebuilding of the physical apparatus is relatively straight forward because a setupalready exists at Cypress. The apparatus will need to be replicated locally andshouldn’t take more than 8 hours to build; less than a weekend’s worth ofwork.The demonstration itself will be a faraday cage set up on a table. Insideof it will be the table controlled by stepper motors with an example deviceunder test attached to the top of it that exhibits interesting noisecharacteristics, such as an older, non-shielded PSoC or an ATMEL chip. Dataruns will be taken repeatedly of the given device to show the function of thesetup. There will also be measurements of other devices displayed to showhow different measurements look.6

Sustainability for this project will be standard fare for electronics. Thepower consumed by the setup will be mostly dominated by the PC controllingthe setup. No consumables are used in the process, so barring parts that needto be replaced, waste will be kept to a minimum. No hazardous materials areused when taking the measurements and no fuel sources are needed (otherthan wall outlets to provide electricity).ELECTRICAL SPECIFICATIONS:System SpecificationsMeasurement Accuracy .1 mm RepeatabilityMeasurement Resolution .5 mm stepsOperating Temperature Range 0‐100° FSize Limit under 1 m 3CommunicationUART through USBCage Mesh size

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