ECE Lab 4 Solution

Purpose:

Using timer/counters in all modes: timer, pwm, oscillator

Using TCNT0 as a realtime clock.

Building the audio amplifier subassembly.

Accessing the LCD display.

Making binary to bcd to ascii conversions.

Using the analog to digital converter.

Understanding human light sensitivity levels

To fix anything else that seems flaky before we go on!

Creating user interfaces




Project Specification:

*Write code to implement an alarm clock which continuously displays the

time in minutes and hours on the LED display.

*Using a CdS cell and the ADC, implement a PWM LED brightness controller.

Use a PWM output from TCNT2 which drives PORTB bit seven to implement

the dimming function. PORTB bit seven was already connected in lab 2.

*Dimming should not flicker at dimness boundaries

*The dimming should be pretty continuous to the eye.

*The display colon will blink on and off at 1 sec intervals.

*The time and alarm settings are to be user adjustable using the

push buttons and/or encoders. How you implement this user interface is

completely up to you. You may petition for bonus points if your UI is

clever. Please label your push buttons for testing.

*The alarm sound is to be a tone or annoying beep at a frequency of your

choice. Use TCNT1 as the programmable oscillator to create the alarm tone(s).

You may use any Port C pin or Port D pins 2-7 as the output for the alarm

output.

For extra credit, you can implement the alarm as the Beaver fight song.

*You will implement a 10 minute snooze function....but please set it up

for 10 seconds for testing purposes.

*You may implement your clock as 12hr or 24hr format. Making this switchable

could add some extra credit.

*The alarm armed indication is to be displayed on the LCD. It could simply

read "ALARM".

*An alarm armed indication on the LED display should also be implemented.

Again, its your choice on how this is done.

*The alarm will share the audio amplifier with the radio. The alarm should

thus sound at the same level as the radio. The radio output level is

approximately 75mVpp. Provide an extra input to both channels of the audio

amplifier. Use the OPAMP as a summer for these signals.

*Determine how to set the input amplitude to the audio amplifier appropriate

for our system. We are aiming for about 100-200mW RMS (8 ohms) of audio at

the speakers.

*The audio level is determined by the voltage of a pin on the audio amplifier.

Create this voltage with a PWM created by TCNT3.




Before Lab:

*Draw the schematic of the analog circuitry that allows you to play either

the alarm or radio through the audio amplifier. Make sure the alarm goes

through both channels of the amplifier.

*Determine how you are going to implement the user interface to the clock.

Some questions to ask are...

-increment the count by encoders or buttons

-how do you distinguish AM and PM on the alarm?

-how long should the alarm go off?




Assembly:

*Build circuit that will merge the alarm input to the audio amplifier on the

protoboard. The audio amplifier will also be placed on the protoboard.

This will require some OPAMP design.

*CdS cell should be located on the protoboard.

*You should fix anything that is marginal, nearly broken, loose

or is not quite right in software or hardware.




Software:

*Write out pseudocode or flow chart of your software (suggestion).

*Use the 32kHz oscillator to operate the clock timebase for TCNT0.

 

Testing:

*Clock and alarm are settable.

*Clock keeps correct time. (Test over 24hrs if possible.)

*Alarm goes off as it should.

*10sec snooze function works correctly.

*Dimming feature is smooth.




What to show for your work:

*Schematic diagram you used to wire up the opamps and amplifier.

*Printout of your code. Use a2ps format.

*Demonstrate working system to TA by before next lab.




Grading:

*Circuit function +70% (demo system in lab)

-performs as expected, clock keeps time, UI is good

-adjustments not smooth -deduct 10%

-dim display/flickers -deduct 5%

-jumpy dimming feature -deduct 5%

-awkward user interface -deduct 5%

-other abnormality -deduct 5% (for each distinct problem)




*Documentation +30%

-complete, neat, correct

-code well written, commented

-sloppy documentation -deduct 10%

-poorly commented code -deduct 10%




Lab weighting = 0.20