You will produce a sine wave using the PWM output of timer1. The frequency will be set from a keyboard. A LCD display will show the peak-to-peak voltage and frequency of the signal determined from analog-to-digital (A/D) converter measurements of the signal. Timer0 will be used as the timebase for the A/D converter.
The PWM output should be lowpass-filtered using an RC circuit with a time constant at least ten times the PWM pulse-time. The A/D input is limited to 0-2.0 volts, while the output of the RC circuit will be centered around Vcc/2. Also, the A/D input impedance is only about 6Kohm. We thus need a circuit to:
The A/D converter input should be connected to the output of the op amp. See the A/D documentation for a schematic.
As in Lab 5,
You will need to get user input from a keypad with the following configuration.
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.As in lab 5, the Liquid Crystal Display (LCD):
LCDpin Connection ------ ---------- 1 gnd - Port A 2 +5 volts - PortA7 3 trimpot wiper 4 PortD6 5 PortD5 6 PortD4 7-10 no connection 11 PortD0 12 PortD1 13 PortD2 14 PortD3
Write a program which will:
to the LCD. The
V = x.xx yy
F = zzzz yy
x.xxrepresents a four digit ascii number determined from the peak-to-peak voltage. The
zzzzrepresents the frequency. The
yyrepresents one of two strings: "V " or "Hz".
When you demonstrate the program to a staff member, you should exercise the keyboard commands and show that the measurement displayed on the LCD is correct. The TA will probably supply a waveform for you to analysis.
Your written lab report should include: