Wenton Davis' CTU EE341 Page

User accounts on my server

Some goodies for my EE341 class.  Just in case a few people aren't familiar with u*ix, here are some basic (important) things to get (just barely) started.  I havefound what seems to be a reasonable source for students who use windows to download PuTTY from.  Students can use telnet to access my machine, but are still encouraged (for security reasons) to use PuTTY in SSH mode ("Secure SHell").  This can be found at http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html If you type "telnet thoughtmountain.com" from your command line, you will be connected to my server.  HACKER WARNING: Everything is monitored and logged, and some of the security subsystems WILL counter attack if the system security is provoked enough!

GNUcap (version 0.35)

I am going to create user accounts for each of my students to be able to use gnucap, a circuit analysis (spice) tool.  Although many students use PSpice, which is a good tool, I still enourage people to have as broad knowledge as possible, so I am making gnucap available, also.  There is some documentation for gnucap available.  The PDF format is available from http://gnucap.org, or in HTML format from their online source.  Gnucap is a text-based spice, so when you run it, you need to tell gnucap which file to use.  If you have defined a circuit in a file called "lowpass.ckt" then you need to type:

    gnucap -b lowpass.ckt

Note that the -b is included to inform gnucap to run the program in "batch" mode, meaning run the analysis automatically.  The default is to run in "interactive" mode, in which the system will load the circuit description, but wait for user interaction to decide what to do with it.  This is very useful for when the users need to make changes to the circuit and rerun the same test, but very confusing to use when you're not used to it.  My description of how to use gnucap can be found here.

The Project

The project for this class will be to design circuits to detect DTMF ("Dual Tone Multiple Frequencies") tones.  The keypad on a telephone is used to produce two frequencies.  Each row on the keypad has a unique frequency assigned to it, and each column has a unique frequency.  These frequencies are added together and sent over the telephone line.  A DTMF decoder is needed in the receiving end to determine which button was pressed.  To do this, it needs to detect which row frequency is received and which column frequency is received.  Please visit this page at Wikipedia to see a chart of the tones generated by the DTMF phone ecryption.  (Also note that there are 4 additional buttons in the touchpad system that are not used on telephones.)

The project will require students to design (not build) a circuit that will detect each of the tones used in the detector/decoder.  The final turnin should include a schematic diagram, spice simulation(s), demonstrating detection of each tone, and a description of what the plan would be to start building the circuit using real components.

A few sections being developed:

Laplace - large table of various Laplace tramsform pairs
Applying Laplace to circuits - using Laplace in circuit analysis
Filters - description of various filter concepts (high-pass, low-pass..., cutoff, etc.)
Filter Designs - description of classes of filters (Butterworth, Chebyshev.....)
Bode Plots

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If you need to reach me, you can always email me at email (wenton@ieee.org)