E11 Lab 3
Procedures
2008

Procedure:

Part 1: The touch screen

On the I/O box:

connect Ground and +5V to the corresponding places on the touch screen apparatus:

Make the following measurements (using a voltmeter):

• Measure and record the +5V coming from the IO board.
• Set P0.0 input to 0V (logic 0 - low voltage)
  • measure and record the voltage on pin 3 of the 74HC125 (one of the two integrated circuits on the board connected to the touch screen), this is voltage on right side of the display (this should be near 5V - refer to prelab),
  • measure and record the voltage on pin 6 of the 74HC125, this is voltage on left side (this should be near 0V),
  • measure and record the voltage on C1 when the screen is not being touched,
  • measure the voltage on C1 as you touch the screen in the twelve locations that exist at the intersection of the heavy lines on the graph paper behind the screen (note, each of the labels is one of the heavy lines):
    
    
    Fill in a table like the one below.
    

    Table 1	left	mid-left	mid-right	right
    top
    middle
    bottom

  • What pattern do you see?  Is this what you expected?
    
    
• Set P0.0 input to +5V (logic 1 - high)
  • measure and record the voltage on pin 8 of the 74HC125, this is voltage on the top of the display,
  • measure and record the voltage on pin 11 of the 74HC125, this is voltage on the bottom,
  • measure and record the voltage on C0 when the screen is not being touched,
  • measure the voltage on C0 as you touch the screen in the twelve locations shown (fill in a table like the one below).
    

    Table 2	left	mid-left	mid-right	right
    top
    middle
    bottom

  • What pattern do you see?  Is this what you expected?

Now, hook up the C0 output to the Chan 0 input on the I/O box (this is one of the A/D inputs).  Connect C1 to Chan 1.  Connect P0.0 on touch screen board to P0.0 on I/O box (this is a digital output from the I/O box); make sure to disconnect this from ground or +5V.  (Some useful MatLab code snippets - Note: the code is (for the most part) uncommented.  If you choose to use any of it, please add comments, as appropriate, before turning it in.)

• Program 1:
  • Write a program that:
    • Initializes the data acquisition (or DAQ),
    • sets P0.0 low,
    • starts a loop that runs for 10 seconds, and within the loop reads the value from Chan 1 and displays it.
    • closes the data acquisition
  • Make sure you are happy with the results of the program.
• Program 2:
  • Write a program that:
    • Initializes the data acquisition,
    • sets P0.0 high,
    • starts a loop that runs for 10 seconds, and within the loop reads the value from Chan 0 and displays it.
    • closes the data acquisition
  • Make sure you are happy with the results of the program.
• Program 3:
  • Write a program that:
    • Initializes the data acquisition
    • starts a loop that runs for 10 seconds, and within the loop:
      1. set P0.0 and read inputs to get the x and y location of the stylus
      2. plot the location on the screen
    • closes the data acquisition
• Program 4 (this is the only program that needs to be turned in).
  • Write a program that allows you to write your name (or anything else) on the screen - you should be able to do a simple modification of "Program 3" wherein the dots are not erased. 
    Hint:  What does the MatLab command "hold on" do?  You may also need "hold off."
• Extra credit (complete any or all of the following):
  1. Change the code so it doesn't display the circle when the screen is not being touched.
  2. Connect the dots with a line.
  3. Average several consecutive values (e.g., the last 5 or 10 or ...) so that there is less jitter.

Part 2: Building a circuit permanently

For this part of the lab you will build a simple circuit with a couple of oscillators.  We will analyze it next week.  Ed Jaoudi will help you solder together a version of the circuit shown below.  Directions are here.

 pdf version of circuit diagram.

Before You Leave

Make sure the lab is cleaned up, and that you have all the information you will need for your report.

email me with any comments on how to improve the information on this page (either presentation or content), or to let me know if you had any particular difficulties with this lab.

Back