EENG 383
Microcomputer Architecture and Interfacing
Fall 2016
Lab 3 – 7 Segment Display
September 15, 2016
In this lab you will use the HCS12 microcontroller on the SSMI board to detect the presence of
an object using a “break-beam” sensor, and display a count of detections on a 7 segment display.
1
Prelab Questions (complete prior to coming to lab)
Answer the following questions.
1. Refer to the data sheet for the SSMI board. For this project we need to supply +5V
regulated power to the sensors. The SSMI board can generate +5V power through a
voltage regulator (LM2931T-5 at position U5). Which pin of H1 does this voltage come
out to? Note that jumper JB1 should be positioned between pins 2 and 3.
2. Refer to the datasheet for the TSOP4838 IR receiver. Determine which pin numbers are
Vs (supply voltage), ground, and output signal. When the receiver is detecting an input
light beam, is the output signal high or low?
3. Refer to the datasheet for the TSAL6200 IR LED. What wavelength of light does the
diode emit? In comparison, what are the wavelengths of visible light?
4. Complete the following table which shows which segments must be illuminated to
display the hex digits 0..F.
5. Draw a schematic of your microcontroller connected to a 7 segment display using pins
PT0..PT6, and the TSOP4838 IR receiver connected to PT7. Include pin numbers, and
don’t forget the resistors.
74HC244
Digit
abcdefg
a
b
c CS12
d
e
f
H
0
0x7E
1
1
1
1
1
1
1
0x30
0
1
1
0
0
0
PB6
2
0x6D
1
1
0
1
1
0
3
0x79
1
1
1
1
0
0
PB5
4
0x33
0
1
1
0
0
1
PB4
5
0x5B
1
0
1
1
0
1
PB3
6
0x5F
1
0
1
1
1
1
PB2
7
0x70
1
1
1
0
0
0
8
0x7F
1
1
1
1
1
1
PB1
9
0x7B
1
1
1
1
0
1
PB0
A
B
C
D
Figure 4.17 D riving a
E
F
Figure 1. Codes for the seven segment display.
1
g470  each
0
0
a
1
1
b f
1
c
1
d
1
e e
0
1
f
1
g
a
b
g
c
d
com m on cathode
single seven -segm ent display
EENG 383
2
Microcomputer Architecture and Interfacing
Fall 2016
Regulated +5V Power
For the remainder of the semester, it will be convenient to connect a pair of wires from H1 to the
protoboard on the SSMI board, to supply +5V regulated power and ground to your circuits on the
protoboard. The SSMI board has a voltage regulator that takes the +9V unregulated power from
the adapter, and generates +5V regulated power. This signal is called “Vsharp” and comes out,
via jumper JB1, to header H1.
Connect a red wire from the pin corresponding to “Vsharp” on header H1, to the red protoboard
row. Connect a black wire from ground “Vss” on header H1, to the blue protoboard row. Verify
with the multimeter that there is 5V between these two rows. Just leave these wires in place for
the remainder of the semester, so that the protoboard always has power.
The voltage regulator that produces Vsharp only produces up to 100 mA. This is enough to
power logic circuitry, LEDs, etc, but it is not enough to power motors.
3
Seven Segment Display
Connect the seven segment display to Port T, using seven current limiting resistors (or just use
the resistor DIP part provided in the kit).
Sign-Off 1: Let the instructor check your connections. Then connect the power adapter to the
board.
Write a C program to have your display count up from 0 to F (and then reset to 0), with each
digit displayed for one second. Have the program repeat forever. You may find it helpful to first
manually write the various codes to Port T to make sure that the correct LEDs light up (recall
how you did this in the previous lab).
Sign-Off 2: Demonstrate the program to the instructor.
4
Break-Beam Sensor
As discussed in lecture, a “break-beam” sensor can be constructed using an infrared (IR) light
emitting diode and an IR receiver. When an object comes between the transmitter and receiver,
it “breaks the beam” and this event can be detected and counted. To avoid unwanted sensitivity
to ambient light, we will use a 38 kHz modulated signal for the transmitter. The receiver is
designed to detect only IR light that is modulated by this frequency. The range of the receiver
can be several meters or more, with a reasonably bright transmitter.
2
EENG 383
Microcomputer Architecture and Interfacing
Fall 2016
We will generate a 38 kHz signal using the function generator. Connect the BNC adapter to the
“TTL” output of the function generator. Check the frequency of the output signal with the
oscilloscope and adjust the function generator to generate a 38 kHz signal.
Get a little protoboard from the lab instructor and put the IR LED from your kit on the
protoboard. Connect the output of the function generator to the IR LED in series with the 80
ohm resistor in your kit.
Now put the TSOP4838 IR receiver on the protoboard on the SSMI board, and connect its power
and ground pins. Power should be connected to +5V coming from “Vsharp”. With the
transmitter light shining on the receiver, check the signal output of the IR receiver (with the
oscilloscope or multimeter). Verify that the output signal changes when the beam is blocked.
Now connect the output pin of the IR receiver to pin PT7 of the microcontroller. Modify your
program so that instead of counting up every second, it only counts up when you get a new
detection1 from the break beam sensor. The count of detections should be displayed on the 7
segment LED display. Of course, the 7 segment display can only display up to 15 decimal, so
above 15 it will wrap around to zero (i.e., it displays the count modulo 16).
Sign-Off 3: Demonstrate the program to the instructor.
Include in your report:
 A description of the circuits used and the schematics
 A flowchart or pseudo code describing the algorithms
 The C language programs (with comments). Report the size of your program, in terms of
the number of lines of source code, and the number of bytes of machine code.
1
The program should count each “break” only once, not multiple times.
3
EENG 383
Microcomputer Architecture and Interfacing
Fall 2016
Lab 3: 7-Segment Display
Name: ________________________________Name: ________________________________
Task
Description
Sign-Off 1
Verify 7-Segment Display Implementation
Sign-Off 2
7-Segment Display Counter
Sign-Off 3
Demonstrate break beam sensor program to the instructor
Initials
5 Rubric
Deliverables
17 pts Pre-Lab
Program with
Flowchart/psuedocode
/7
Schematic
/ 5 Demonstrations
Circuit Explanation
/5
Composition
5 pts
Questions
5 pts
/5
23 pts
Sign-Off 1: 7-Segment Implementation
/5
Sign-Off 2: 7-Segment Display Counter
/10
Sign-Off 3: Break beam program
Total
/ 50 pts
4
/8