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EE 319K
Introduction to Microcontrollers
Lecture 11: DAC, Sound on 9S12,
Lab7(Music/Pacemaker)
11-1
Digital to Analog Conversion
 Examples
 Signal generation (sound, image, touch…)
 Output to affect external devices (power, flow, heat…)
 The DAC precision is the number of distinguishable DAC
outputs
 (e.g., 16 alternatives, 4 bits).
 The DAC range is the maximum and minimum DAC
output
 (0 to 5V).
 The DAC resolution is the smallest distinguishable change
in output.
 (5V/16 =0.31V)
 Range(volts) = Precision(alternatives) * Resolution(volts)
 The DAC accuracy is (Actual - Ideal) / Ideal
Ramesh Yerraballi
11-2
2-bit DAC - Two Designs
N
0
1
2
3
Q1
0
0
5
5
Q0
0
5
0
5
V1(V)
0.00
1.25
2.50
3.75
V2(V)
0.00
1.67
3.33
5.00
10k
Q1
Q0
20k
10k
V1
20k
Q1
Q0
20k
V2
*Assume VOH of the 9S12 is 5V and VOL is 0V
Ramesh Yerraballi
11-3
4-bit DAC
N
0
1
2
8
15
Q3
0
0
0
5
5
Q2
0
0
0
0
5
Q1 Q0
0 0
0 5
5 0
0 0
5 5
theory
5*0/15
5*1/15
5*2/15
5*8/15
5*15/15
Vout (V)
0.00
0.33
0.67
2.67
5.00
Vout = (8*Q3 + 4*Q2 + 2*Q1 + Q0)/15
where Qn is 5V or 0V
static
testing
6812
6812
bit3
bit2
Ramesh Yerraballi
dynamic
testing
bit3
Vout
bit2
voltmeter
bit1
bit1
bit0
bit0
I out
speaker
11-4
Sound Basics
Humans can hear from about 25 to
20,000 Hz.
Middle A is 440 Hz
Other notes on a keyboard are
determined
440 * 2N/12
"N" is number of notes up or down from
middle A.
Middle C is 261.6 Hz.
Music contains multiple harmonics
Ramesh Yerraballi
11-5
Sound
period
pitch = 1/period
loudness
The loudness and pitch are controlled by the amplitude and frequency.
A 440Hz sine wave generated with a 4-bit DAC. The plot on the right is the
Fourier Transform(frequency spectrum dB versus kHz) of the data plotted on the left.
Ramesh Yerraballi
11-6
Music
period
A waveform shape that generates a trumpet sound.
Ramesh Yerraballi
11-7
…Music
330 Hz
0.5s
330 Hz
0.5s
523 Hz
1.0s
You can control the amplitude, frequency and duration
of each note (not drawn to scale).
330 Hz
0.5s
330 Hz
0.5s
523 Hz
1.0s
The amplitude of a plucked string drops exponentially in time
Ramesh Yerraballi
11-8
…Music
Sound Amplitude
2
1
0
-1
-2
0
0.005
0.01
Time (sec)
0.015
0.02
A simple chord mixing the notes C and G
Ramesh Yerraballi
11-9
Song
How much memory does it take to store a song?




3 minutes
Stereo Channels
44 kHz
12-bit per channel
How many bus cycles does it take to output one
value?




Fetch data from memory
Decompress
Filter/amplify/mix/envelope
DAC speed
Ramesh Yerraballi
11-10
Lab7: Sound
Debugging: Use a DC motor to test the
voltages being output to the analog out
Connect the PH3-0 lines to power a DC
motor
Connect a scope to view this voltage as a
function of time
Once you are sure your DAC_Out is
doing what it is supposed to, then go
ahead and implement the piano keys
Ramesh Yerraballi
11-11
Sine Wave with period T
 Periodic Interrupt every T/32
 Output next entry in below table on interrupt
fcb
fcb
fcb
8,9,11,12,13,14,14,15,15,15,14
14,13,12,11,9,8,7,5,4,3,2
2,1,1,1,2,2,3,4,5,7
4-bit DAC output
SinTab
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
4-bit sin table
0
1
2
3
4
5
6
7
theta (radians)
Ramesh Yerraballi
11-12
Lab7: Pacemaker
Debugging: Use a DC motor to test the
voltages being output to the analog out
Connect the PH3-0 lines to power a DC
motor
Connect a scope to view this voltage as a
function of time
Once you are sure your DAC_Out is
doing what it is supposed to, then go
ahead and implement a DAC circuit
Ramesh Yerraballi
11-13
Ventricular Output pulse
 Ae-t/τ (Amplitude A=5; τ=2)
 Periodic Interrupt every t2/101
 Output next entry in below table on interrupt
VentOut
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
15,15,15,15,14,14,14,14,14,14
14,13,13,13,13,13,13,13,13,12
12,12,12,12,12,12,12,11,11,11
11,11,11,11,11,11,10,10,10,10
10,10,10,10,10,10,9,9,9,9
9,9,9,9,9,9,9,8,8,8
8,8,8,8,8,8,8,8,8,8
7,7,7,7,7,7,7,7,7,7
7,7,7,7,6,6,6,6,6,6
6,6,6,6,6,6,6,6,6,6,6
16
14
12
10
8
"Orig"
6
Approx
4
2
0
0.12
0.24
0.36
0.48
0.6
0.72
0.84
0.96
1.08
1.2
1.32
1.44
1.56
1.68
1.8
1.92
0
Ramesh Yerraballi
11-14