EE 476: Laboratory 5

Sinewave generator.

You will produce a sinewave generator which is controlled by a 16-key keypad and which shows the frequency on a LCD display.

You will need to build a simple digital-to-analog converter as shown below.

The Liquid Crystal Display (LCD):

A 16 character, one line (16x1), LCD display will show the frequency for the sinewave generator. 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, you can use port pin 10 for power. You will need a 10k or 20k trimpot to adjust display contrast as shown in the following program. The C 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.
• The character representation is identical to ASCII codes for numbers, letters and most symbols. Refer to the data sheet above for a complete listing.

Here is a sample C code which outputs a sinewave of a user-selectable, fixed frequency. The program organization page has an example of squarewave synthesis in C and ASM. The same program is recoded using a mixture of C and ASM (as you will need to do for this assignment).

Be sure to read the serial communication page if you are going to debug using the time-honored printf.

Write a program and build a circuit which will:

• Generate sinewaves with 16 samples (or more) per cycle and a frequency range from 500 to 5000 Hz (or more). The sinewaves should be built from 8-bit samples and converted to a voltage with a DAC. Note that you will need to use assembly language ISRs to get much above 2.6 kHz.
• Scan the keypad for one of three commands (which could be single keystrokes):
  • stop the sinewave
  • start the sinewave
  • clear current entry
• 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. Clear entry should erase any digits on the display.

When you demonstrate the program to a staff member, you should exercise the keypad commands and show that the generated frequency is correct. Full credit will be given only if you can generate sinewaves above 5 kHz (with at least 16 samples/cycle).

Your written lab report should include:

• The scheme you used to decode commands.
• The scheme you used to convert the ASCII input to a frequency.
• A heavily commented listing of your code.
• A schematic of your circuit.
• A waveform captured from the oscilloscope showing the waveform you generated.