Electronic Lab

ETB101 - Digital Electronics Laboratory Manual Introduction Laboratiry is a necessary part of the course at which attendance is compulsory. Attendance or absence of students will be noted by the laboratory demonstrator. Each laboratory experiment is marked and the average of these marks will contribute to 15% of your overall mark for the ETB101 module. Students must attend all scheduled laboratory sessions. Students are required to be punctual - latecomers may be refused entry. Pre-lab questions must be answered prior to the laboratory session. Answer all questions and all sections of the laboratory. Refer to the Undergraduate Laboratory Handbook for general instructions on conduct of laboratories. Here are some guidelines to help you perform the experiments and to submit the reports: Read all instructions carefully and carry them all out. Ask a demonstrator if you are unsure of anything. Record actual results (comment on them if they are unexpected!) Write up full and suitable conclusions for each experiment. If you have any doubt about the safety of any procedure, contact the demonstrator beforehand. THINK about what you are doing! Most experiments involve the use of the power supply, the oscilloscope, a signal generator, the voltage measurement unit and your breadboard.

The Breadboard The breadboard consists of two terminal strips and two bus strips (often broken in the centre). Each bus strip has two rows of contacts. Each of the two rows of contacts are a node. That is, each contact along a row on a bus strip is connected together (inside the breadboard). Bus strips are used primarily for power supply connections, but are also used for any node requiring a large number of connections. You will build your circuits on the terminal strips by inserting the leads of circuit components into the contact receptacles and making connections with 22-26 gauge wire. There are wire cutter/strippers and a spool of wire in the lab. It is a good practice to wire +5V and 0V power supply connections to separate bus strips.

Fig 1. The breadboard.

The 5V supply MUST NOT BE EXCEEDED since this will damage the ICs (Integrated circuits) used during the experiments. Incorrect connection of power to the ICs could result in them exploding or becoming very hot - with the possible serious injury occurring to

the people working on the experiment! Ensure that the power supply polarity and all components and connections are correct before switching on power .

Building the Circuit Throughout these experiments we will use TTL chips to build circuits. The steps for wiring a circuit should be completed in the order described below: Turn the power off before you build anything! Make sure the power is off before you build anything! Connect the +5V and ground (GND) leads of the power supply to the power and ground bus strips on your breadboard. The +5V supply may be found on the bottom centre of the power supply with the black switch at the +5V fixed position. Before connecting up, use a voltmeter to check that the voltage does not exceed 5V. Plug the chips you will be using into the breadboard. Point all the chips in the same direction with pin 1 at the upper-left corner. (Pin 1 is often identified by a dot or a notch next to it on the chip package) Connect +5V and GND pins of each chip to the power and ground bus strips on the breadboard. Select a connection on your schematic and place a piece of hook-up wire between corresponding pins of the chips on your breadboard. It is better to make the short connections before the longer ones. Mark each connection on your schematic as you go, so as not to try to make the same connection again at a later stage. Get one of your group members to check the connections, before you turn the power on. If an error is made and is not spotted before you turn the power on. Turn the power off immediately before you begin to rewire the circuit. At the end of the laboratory session, collect you hook-up wires, chips and all equipment and return them to the demonstrator. Tidy the area that you were working in and leave it in the same condition as it was before you started.

Common Causes of Problems Not connecting the ground and/or power pins for all chips. Not turning on the power supply before checking the operation of the circuit. Leaving out wires. Plugging wires into the wrong holes. Driving a single gate input with the outputs of two or more gates Modifying the circuit with the power on. In all experiments, you will be expected to obtain all instruments, leads, components at the start of the experiment and return them to their proper place after you have finished the experiment. Please inform the demonstrator or technician if you locate faulty equipment. If you damage a chip, inform a demonstrator, don't put it back in the box of chips for somebody else to use. If you locate any errors in this manual, please ask Mr Fahamuel or your module master.

Example Implementation of a Logic Circuit Build a circuit to implement the Boolean function F = /(/A./B), please note that the notation /A refers to . You should use that notation during the write-up of your laboratory experiments.

Quad 2 Input 7400

Hex 7404 Inverter

Fig 2. The complete designed and connected circuit Sometimes the chip manufacturer may denote the first pin by a small indented circle above the first pin of the chip. Place your chips in the same direction, to save confusion at a later stage. Remember that you must connect power to the chips to get them to work.

ETB 101 - Digital Electronics Laboratory Laboratory Exercise 1. The AND, OR Gates Objectives: To investigate AND, OR gate operation. To study some fundamental laws of Boolean Algebra. To become familiar with logic circuits.

Introduction This is the introductory laboratory session, to allow you to become familiar with very basic digital circuits and the equipment that you will use for the remainder of the experiments. Before you even attempt this laboratory, you must have read the lab manual. This details how you will connect components together on the breadboard and how the inner connections of the breadboard are structured. It also details laboratory safety information. The demonstrator may quiz you on your knowledge of the Laboratory Manual.

Equipment The equipment you require is as follows: Your lab notebook Your own lab kit (bought from the technicians). Power supply, Digital voltmeter (available at the desks) Collect hook-up wire and ICs from demonstrator (74LS08 and 74LS32)

Pre-Laboratory There are several tasks that you must perform prior to setting this laboratory: 1. Read the laboratory assignment in full. 2. Draw up the truth tables for a 2-input AND and a 2-input OR gate. 3. Explain the Boolean algebra Associative, Commutative and Distributive Laws. 4. Derive a Truth-Table for the function F=AB+CD.

Useful Chip Diagrams:

7408(AND)

7432(OR)

The Laboratory: Section 1. AND Gate Implementation (a) Connect one of the 2-input AND gates (74LS08) as shown in Figure 1. Remember to power the Vcc and GND terminals of the chip. Remember also to leave the power supply off, until you are sure that your circuit is wired correctly.

Figure 1. The 2-input AND gate. (b) Vary the inputs A and B (i.e. 0 and +5V) to obtain all the possible combinations and complete the truth table (as below) for the AND gate. Measure the output F using a Digital Voltmeter. Give the exact voltages that you obtained for each state of the gate.

A 0 0 1 1

V B F (actual voltage) 0 1 0 1

(c) The 2-input AND gate can be extended to a 4-input AND gate as shown in Figure 2. Connect the gates as shown and generate the values for the truth table below.

Figure 2. The 4-input AND gate, built using 2-input AND gates.

A 0 0 0

B 0 0 0

C 0 0 1

D F 0 1 0

0 0 0 0 0 1 1 1 1 1 1 1 1

0 1 1 1 1 0 0 0 0 1 1 1 1

1 0 0 1 1 0 0 1 1 0 0 1 1

1 0 1 0 1 0 1 0 1 0 1 0 1

(d) Design a 3-input AND gate that is composed of 2-input AND gates. Measure the outputs and generate a truth table. Describe your design. How would you create a 5 input AND gate?

Section 2. Associative and Commutative Laws (a) Connect AND gates as shown in Figure 3 to implement the Boolean equations F = A(BC) and G=(AB)C.

Figure 3. Proving The Associative Law. (b) Vary inputs A, B, and C to obtain all of the possible combinations and to check the associative law: A(BC) = (AB)C. Fill in the truth table below: A 0 0 0 0 1 1 1 1

B 0 0 1 1 0 0 1 1

C F G 0 1 0 1 0 1 0 1

(c) How would you demonstrate the Commutative Law using logic gates? Describe your design and implement it using logic gates. Check all the combinations of inputs and the corresponding outputs to insure that it works. Show the resulting truth table.

Section 3. Laws of Boolean Algebra (a) To demonstrate the Distributive law, connect AND, OR gates as shown in Figure 4. Vary the inputs A, B and C to obtain all possible combinations and check that the outputs F and G are identical.

Figure 4. The Distributive Law. Give the outputs in a truth table as shown below: A 0 0 0 0 1 1 1 1

B 0 0 1 1 0 0 1 1

C F G 0 1 0 1 0 1 0 1

Section 4.Disconnected Inputs (a) Check the behaviour of an OR gate when one of its inputs is open (disconnected - not connected to ground). Check the behaviour when two of the inputs are open. Describe what you observed. Do the same for an AND gate.

Section 5. Boolean Equations (a) 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) and 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. Implement the circuit for this logic equation and complete the Truth Table below. A 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1

B 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1

C 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1

D F 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

Section 6. Analysis of Results

(a) Are the Associative and Commutative laws obeyed in practice? Yes No Don't Know (b) The following truth table represents which Boolean equation? A

B

F

0

0

0

0

1

0

1

0

1

1

1

0

F=A+B F = A.(/B) F = (/A).B Don't know (c) Is it possible to build an AND gate with more than 2 inputs using a single 7408 chip? Yes No Don't Know (d) How many 2-input OR gates are required to produce an OR gate with N inputs? N N+2 N-2 N-1 Don't Know

Section 7. Conclusions State briefly, but clearly, what you have gained from this assignment. Outline aspects that you have noted within the experiment outside of the questions asked. Make comments on the procedure of the lab .