EE 476: Laboratory 1

Reaction Time Tester.

Introduction.

This assignment introduces you to the software and hardware development tools you will use this semester to work with the Atmel AT90-series microcontroller (MCU) chips. You will use the STK500 development board to build a human reaction time tester. The STK500 pushbuttons, an external LCD, and the mcu will be used to see how fast you can push a button after a light flashes.

1. After you define a new project, you can add a C source file and edit it.
   1. Save this code (from the Program Organization page) into your directory. This program blinks LEDs and responds to buttons. It is organized as three task subroutines. You will modify this code in the assignment below.
   2. In the Codevision file menu choose to make a new file. When the prompt comes up, choose Project. When asked if you wish to use CodeWizard, decline the offer. At this point, you have made a new project, now you need to configure it. The configure dialog should be open but if it is not, under the Project menu, choose Configure...
   3. In this dialog box, in the Files tab, add the source code to the project you just defined.
   4. In the Compiler tab, set the Chip type to Mega32.
      Set clock speed to 16 MHz.
      Set (s)printf features to int,width.
   5. In the After make tab, set the Program the Chip checkbox.
      You may need to uncheck the Check Signature box.
      Then close the configure dialog.
   6. Click on the compile icon. A message window will open to tell you if there are errors in the code. If there are errors, The open the listing file to see where they are. If the compile is successful, you should be able to download the program to the STK500 board and see some blinking LEDs.
2. Connect the LCD (see below) and run the LCD test program. You should see a counter and a moving dot.
3. You will need to generate a time base for measuring reaction times. Most people have a reaction time in the range of 100 mSec to 200 mSec, but this can be quite variable, up to several hundred mSec.I suggest that you use the multiple task timing scheme from this code.
4. Remember that a switch which is pushed reads back a logic zero.
5. Use the CodeVision help files to figure out how to store to eeprom.

   The Liquid Crystal Display (LCD):

   A 16 character, two line (16x2), LCD display be used as a numerical display. The display we are using has an industry-standard interface. A more detailed data sheet for a similar display shows the command set. There are several aspects of the display you should note:

   • Connecting the power backwards may destroy it.
     Always check the polarity before connecting the display.
   • The 14 pin header is on a corner of the display. Pin 1 is closest to the edge of the pc-board. The connection pattern is shown below.
     

        [LCD]  [Mega32 pin]
        1 GND- GND
        2 +5V- VCC
        3 VLC 10k trimpot wiper (trimpot ends go to +5 and gnd) 
        4 RS - PC0
        5 RD - PC1
        6 EN - PC2
       11 D4 - PC4
       12 D5 - PC5
       13 D6 - PC6
       14 D7 - PC7 

     Trimpot schematic: Bottom view: Image:
     Adjust the LCD contrast using a small screwdriver to turn the trimpot. You may not need the trimpot to adjust the display contrast. You can try just hooking the contrast control (LCD pin 3) to ground.
   • Since the display only draws about 1-2 mA, you can use port VTG pin for +5 volts. You may need a 10k or 20k trimpot to adjust display contrast connected as shown in the following program. But first, try hooking LCD contrast control (pin 3) to ground.
   • The LCD interface to the mcu is documented in the CodevisionC libraries and in a short C program which you can use to test your LCD connections. Note that this program uses a software delay to time the display, something you can never do if your program has to respond to external events.
   • The character representation is identical to ASCII codes for numbers, letters and most symbols. Refer to the data sheet above for a complete listing.
   • The LCD display is arranged as 2 lines of 16 characters and is addressable on a per-character basis.

• EEPROM
  The Codevision help files explain eeprom, but the summary follows: If you declare a variable of type eeprom and assign it a value when declared, then the variable will be stored in nonvolitile memory. It will be initialized when the program is downloaded to the MCU, but not at RESET time. You can read the variable as often as you like, but you must write it very infrequently, usually only when something unusual happens, like a new high score or a serious error.

• All timing must be done with interrupt-driven hardware timers and not with software wait-loops. DO NOT use the delay function, your program will not work correctly.
• All programs must be in C.

• Produce an C language program based on the example above which:

  1. Upon a reset signal, flash the LEDs on the development board at a few Hz and wait for a button 0 press.
  2. At the button press, turn the LEDs off for about 2 seconds. Figure out a way to make the waiting time random, so that it is harder to predict.
  3. After the variable time delay, turn on the LEDs, start a timer and wait for a button press. (your code should detect the cheating condition of a pressed button at t=0 and respond by returning to the flashing LEDs).
  4. At the button press, compute the time between LED illumination and the button press, display the number of millseconds in decimal on the LCD, then waits. Displayed time should be accurate to 1 mSec.
  5. Returns to the flashing LEDs (number 1 above) when button 7 is pushed.
  6. Stores the fastest time in eeprom and displays it on the LCD. Since eeprom write cycles are limited, only write to the eeprom when there is a new fastest time.

  Be prepared to demo the program you wrote to your TA in lab.

Your written lab report should include:

• Examples of well written labs (a), (b)
• How would you measure time-base accuracy?
• Why did we make you use interrupts rather than wait-loops?
• The scheme you used to detect the pushbutton state. (e.g. polling loop, interrupt)
• Other design aspects of the assignment.
• A heavily commented listing of your code.
• Your reaction times and the reaction time of your TA.