WISE Investments
Electrical Engineering Lab
Digital Logic Laboratory
Dr. Keith Holbert
Electrical Engineering
1
Laboratory Preview
• Next we will go to the lab (GWC 273) to see what these
circuits look like
• First, let’s get a preview of what we expect to see in the lab
• The first thing we’ll look at is the trainer boards used to
build the prototype of our digital circuits
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Trainer Board
• Trainer Board: An electrical device used for rapid
prototyping of electrical circuits
• Our trainer board has:
–
–
–
–
–
Breadboard for making connections
Power supply
Switches
LED (light emitting diode) for signal display
Clock
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Trainer Board
Clock
Connection
and LED
Switches &
connections
Ground
0 volts
Breadboard
region
Power
Supply
+5 volts
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Breadboard
Bus: Terminals Horizontally Connected as Shown
Terminals Vertically Connected
Together as Shown
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Gutter: Electrical Isolation of
Vertical Columns for IC Insertion
5
Integrated Circuit (IC) Chips
Pins are numbered
Notch provides a
reference point
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74LS21
6
+5V
14
A data book gives the pin correspondence and
function schematically
13
12
11
10
9
8
AND
AND
AND
1
2
AND
3
SN74LS08
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4
5
6
7
GND
7
Digital Combination Lock
• Using three AND gates, we can build a combination lock
that requires a four-digit code, specifically: 1 1 1 1, using
the particular 7408 pin connections illustrated below
13
AND
11
4
12
AND
6
10
AND
8
5
9
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Digital Lock Circuit Construction Procedure
1) Insert the two ICs (7408 and 7404) across the gutter portion of the
breadboard with notch to the left.
2) Connect the power supply (+5 V) and pin number 14 of both ICs to a
bus at the top of the breadboard area.
3) Connect the ground (0 V) and pin number 7 of both ICs to a middle bus
of the breadboard.
4) For the 1111 combination, connect the output from switches 1 thru 4 as
inputs to pins 9, 10, 12 and 13 of the 7408.
5) Connect the outputs from pins 8 and 11 as inputs to pins 4 and 5.
6) The output from pin 6 is then connected to an LED.
7) Turn the trainer board ON.
8) Use the 4 switches to control the input values to the digital lock. When
the switches are all on,the LED should be on; otherwise, the LED is off.
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Digital Lock: Build a lock with combination 1111
CLK
FREQ
LOGIC INDICATORS
A
B
C
D
LOGIC SW
X X
YY
E
F
G
H
SW6
SW7
SW8
DATA SWITCHES
SW1
SW2
SW3
SW4
SW5
GND
-12
74LS04
7408
74LS21
7404
+12
+5
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To make the lock with a combination of 0110, we’ll
use inverter gates from a hex inverter chip
+5V
14
13
12
11
10
9
8
1
2
3
4
5
6
7
SN74LS04
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GND
11
Digital Combination Lock
• To build a combination lock whose input (key code)
combination is 0 1 1 0, we use two NOT (inverter)
gates from the 7404 using the pin connections below
13
12
7408
13
AND
11
4
12
AND
6
10
AND
11
10
8
5
9
7404
• Are there other pin connections that could be utilized?
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Digital Lock: Build a lock with combination 0110
CLK
FREQ
LOGIC INDICATORS
A
B
C
D
LOGIC SW
X X
YY
E
F
G
H
SW6
SW7
SW8
DATA SWITCHES
SW1
SW2
SW3
SW4
SW5
GND
-12
74LS04
7408
74LS21
7404
+12
+5
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For the railroad crossing signal,
we will need to use an XOR gate
+5V
14
13
12
11
10
9
8
5
6
7
XOR
1
2
3
SN74LS86
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4
GND
14
RR Crossing Circuit Construction Procedure
1) Insert the two ICs (SN74LS08 and SN74LS86) across the gutter
portion of the breadboard with notch to the left
2) Connect the power supply (+5 V) and pin numbers 14 and 13 of both
ICs to the bus next to the top
3) Connect the ground (0 V) and pin number 7 of both ICs to the bottom
bus
4) Connect the clock to the pin number 12 of both ICs
5) Connect the output from pin number 11 of each IC to a different LED
6) Make sure the knobs on the top row of the trainer board are all turned
to the far left (that is, fully counter clockwise)
7) Turn the trainer board ON. The LEDs should flash back and forth; if
not, a loose connection may exist.
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Build the Railroad Crossing Signal
CLK
FREQ
LOGIC INDICATORS
A
B
C
D
LOGIC SW
X X
YY
E
F
G
H
SW6
SW7
SW8
DATA SWITCHES
SW1
SW2
SW3
SW4
SW5
GND
-12
74LS04
7408
74LS21
7486
+12
+5
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Hardware Laboratory
• Now we are ready to go to the lab (GWC 273)
• You will construct
– a digital combination lock
– a railroad crossing signal
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