Equipment Required:The equipment you will require is as follows:
You should submit your laboratory writeup electronically at: http://moodle.dcu.ie/mod/assign/view.php?id=26111 There is a template document at: Template Document to help you to writeup this laboratory. Remember to turn off your multimeter when not in use as the battery will go flat very quickly. 
This session allows you to gain practical experience of the operation of basic logic gates, both in isolation and in combination to realize more complex boolean functions ("combinatorial logic").
You should study the specific instructions below, in full, in advance of the lab session. Note that, in general, this means that you will also have to research and develop your knowledge of relevant prior concepts, specifically logic gates and boolean algebra (otherwise the instructions below will simply not make any sense...).
You might find it useful to watch this video in advance of the laboratory session:
YouTube Video
At the start of the lab session:
 Selforganise into groups of two at each workstation.
 On a new page in the notebook, fill in an appropriate heading for the lab session, e.g.:
 Digital Electronics: Lab Session 1
 Basic Combinatorial Logic
 Date: 24 Oct 2013
 Partner Name: Sheldon Cooper
The AND Gate
 Connect one of the 2input AND gates (74HC08) as shown in Figure 1. Connect two wires to the A and B inputs of the gate (Pins 1 and 2) and connect these to the 5V rail. Connect the output (Pin 3) to one of the LEDs via a 100 Ohm resistor as illustrated in Figure 1. Remember to connect power to the Vcc and GND terminals of the IC (Pins 14 and 7 respectively). Remember to leave the power supply turned off until you are sure that your circuit is wired correctly. Use the bench supply to give you a 5V fixed supply. Connect some hookup wires to leads using crocodile clips and plug them into the DC 5V fixed inputs on the bottom right of the bench supply.
Figure 1: The 2input AND gate starting configuration.
 Copy the outline truth table below into your logbook. Change the inputs
A
andB
(i.e. 0 and +5V) to obtain all the possible combinations and complete the truth table. Enter both the logical value of the output (0
or1
) and the actual voltage measured using a Digital Voltmeter  Measure voltage across the resistor and the diode to get the actual voltage drop between pin 3 and GND. Your multimeter should be set to measure DC voltage (not the ~ AC voltage setting) in the range of 20V (describes the maximum voltage), so rotate the dial on the multimeter until it is in the DC 20V range. Give the exact voltages that you obtained for each state of the gate. Note that, in TTL logic, any voltage above 2.4V is generally classified as logic1
, and any voltage below 0.8V is generally classified as logic0
. Most of our ICs are either TTL or CMOS.
A 
B 
F 
V (actual voltage) 

0 
0 

0 
1 

1 
0 

1 
1 
 The 2input AND gate can be extended to a 4input AND gate as shown in Figure 2. Connect the gates as shown and generate the values for the truth table below.
A 
B 
C 
D 
F 

0 
0 
0 
0 

0 
0 
0 
1 

0 
0 
1 
0 

0 
0 
1 
1 

0 
1 
0 
0 

0 
1 
0 
1 

0 
1 
1 
0 

0 
1 
1 
1 

1 
0 
0 
0 

1 
0 
0 
1 

1 
0 
1 
0 

1 
0 
1 
1 

1 
1 
0 
0 

1 
1 
0 
1 

1 
1 
1 
0 

1 
1 
1 
1 
Other basic gates
Don't forget to switch off the power supply each time you are breaking down or setting up a new circuit!
The power of NAND
Devise a circuit, using only NAND gates, that implements a 2input AND function. Sketch the circuit in your logbook. Build and test the circuit. Record the results in your logbook. Comment on whether they are as you expected.
Disconnected/Floating (Open Circuit) Inputs
Pick one of the 2input gates. Experimentally test its behaviour when either or both of the inputs is left open circuit (unconnected). Describe what you observe in your logbook.
 Connect AND gates as shown in Figure 3 to implement the Boolean equations
F=A.(B.C)
andG=(A.B).C
.
 Copy the outline truth table below into your logbook. Before doing any
experiments, fill in the column marked
P
with your predicted outputs. Now test this experimentally by varying inputsA
,B
andC
to obtain all of the possible combinations, and filling in the measured values ofF
andG
. Comment on whether the results are as you expected.A B C Predict F Predict G F G 0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
Testing the Distributive Law
To test the Distributive law, connect AND, OR gates as shown in Figure 4. Draw an outline truth table into your logbook, with columns forA
,
B
, C
, P
, F
and
G
. Before doing any experiments, fill in the column marked
P
with your predicted outputs. Now test this
experimentally by varying inputs A
, B
and
C
to obtain all of the possible combinations, and filling in the
measured values of F
and G
. Comment on whether the
results are as you expected.Consider the logic statement: "If Mary obtains permission from her mother or her father and if Joe or Tom pick her up, she may go to the cinema". This statement may be expressed as a Boolean equation using the following Boolean variables:
F
= Mary will go to the cinema (true/false)A
= Her mother will give her permission (true/false)B
= Her father will give her permission (true/false)C
= Joe will pick her up (true/false)D
= Tom will pick her up (true/false)
Then F = (A+B).(C+D)
is the Boolean equation that describes this
statement. Draw an outline truth table into your logbook, with columns for
A
, B
, C
, D
, P
,
and F
. Fill in column P
with your predicted
outputs. Devise a circuit to implement the function F
and sketch it
in your logbook. Build the circuit you have sketched, and test its behaviour
experimentally. Fill in the measured values of F
in your truth
table. Comment on whether the results are as you predicted.
Testing De Morgan's Theorem(s)
 Connect inputs
A
andB
and their inverse (complements)/A
and/B
to AND and OR gates as shown in Figure 5. You will have to use NOT gates (inverters) to obtain the necessary complemented or inverted signals.
Figure 5: Testing De Morgan's Theorem. Note, in the bottom figure you should have an inverter on the inputs.
 In your writeup, present the Boolean logic equations for
F
andG
. Before doing any experiments, draw a truth table showing your predicted values forF
andG
. AreF
andG
equal? Should they be?  Redraw the truth table, but now measure the actual values of F and G for all possible values of A and B, and fill these into the table. Comment on how these results compare with your predicted truth table.
 Consider the boolean function
F = /(A.(/(A./B)))
. Draw an outline truth table in your writeup, with columns forA
,B
,P
, andF
. Fill in columnP
with your predicted values for the function. Now devise a circuit to implement the function. Measure the actual values of the output and fill them in, in columnF
. Comment on whether the results are as you predicted.  Use De Morgan's Theorem(s) to simplify the boolean function
F = /(A.(/(A./B)))
. Devise a circuit to implement the simplified function. Measure the actual values of the output and fill them in. Comment on whether the results are as you expected.
 State briefly, but clearly, what you have learned from this session.
 How did you split the work between yourself and your partner?
 What was the most difficult aspect of the lab?
 State one thing you enjoyed about the session.
 State one thing you disliked about the session.
 Add any final comment of your own.