EE 476: Laboratory 5

Sinewave generator
with keyboard and display.

You will produce a sinewave generator which is controlled by a 16-key keypad and which shows the frequency on a LCD display. The sinewave generator will be based on lab exercise 4.

The STK-200 board has different pinouts on the header connectors. Pin 9 (see below) on the port connectors is Vcc, not ground as it was on the green boards.

This project uses the STK-200 board. Note that the cpu is an AT90S8535. The main differences from the 4414 are:

• TIMSK bits are redefined. See page 20 of AT90S8535. You must modify any code which enables a timer ISR.
• The number and placment of interrupt vectors has changed. See page 15 of AT90S8535.
• Twice as much FLASH, RAM and EEROM
• 8 channels of 10-bit analog to digital conversion on PortA.
• a third clock.

The Keypad:

You will need to get user input from a keypad with the following configuration. Demonstration keypad scanning code is here.

Pin 1  -- row 1 2 3 A
Pin 2  -- row 4 5 6 B
Pin 3  -- row 7 8 9 C
Pin 4  -- row * 0 # D

Pin 5  -- col 1 4 7 *
Pin 6  -- col 2 5 8 0
Pin 7  -- col 3 6 9 #
Pin 8  -- col A B C D

(a) Each switch shorts one row to one column.
(b) Each pin should be connected to one 
    bit of an i/o port.
(c) The i/o port pins will be used both 
    as inputs and outputs. When they are inputs, 
    they should have the pullup resistors
    activated.

A 16 character, one line (16x1), LCD display will be the output for your capacitance meter. The display we are using has an industry-standard interface. A data sheet for a similar display shows the connections. There are several aspects of the display you should note:

• Connecting the power backwards will destroy it.
  Always check the polarity before connecting the display.
• The 14 pin header is on the upper-left corner of the display. Pin 1 is closest to the left edge of the pc-board.
• Since the display only draws about 1-2 mA, use port pin for power. You will need a 10k or 20k trimpot to adjust display contrast.
• The LCD setup code is long but using it is straightforward. You can also use the code to test your LCD connections. The code assumes a 4-bit interface. Lines 7,8,9 and 10 on the display are not used and should be left unconnected. The code shows how to initialize the LCD, issue commands, and write characters.

  LCDpin 	Connection
  ------  ----------
  1	gnd 
  2	+5 volts - From a port pin
  3 	trimpot wiper (the ends of the trimpot go to gnd and +5)
  4	PortD6
  5	PortD5
  6	PortD4
  7-10	no connection
  11	PortD0
  12	PortD1
  13	PortD2
  14	PortD3
  

• The character representation is identical to ASCII codes for numbers, letters and most symbols. Refer to the data sheet above for a complete listing.

Write a program which will:

• Scan the keyboard for one of two commands (which could be single keystrokes):
  • stop the sinewave
  • start the sinewave
• When started, produce a sinewave from the DAC, and display the sinewave frequency on the LCD display.
• When stopped, accept a four digit number from the keypad to set a new frequency, and display the frequency on the LCD.

When you demonstrate the program to a staff member, you should exercise the keyboard commands and show that the frequency displayed on the LCD is correct.

Your written lab report should include:

• The scheme you used to decode the keyboard.
• The scheme you used to convert the frequency to formatted ASCII.
• A schematic of the curcuit you built.
• A heavily commented listing of your code.