0. General Instructions

Introduction to Experiment Exercises and Assignments:

This document provides an introduction and overview of the laboratory activities for the CT2 module. Please read this carefully before beginning the experiment exercises or assignments.

Experiment exercises are work that you must carry out in order to understand the theory in your notes and to become familiar with the practical side of the module. These are not graded, but are necessary for you to complete the assignments.

Assignments are the regular assignments that you will have seen in previous modules; however, in this module there will be practical components to the assignments that you must physically implement. These will be graded, and will contribute to your overall mark for the CT2 module.  

Writing up your assignments:

You must complete the report on each assignment as you are doing the work. It would be useful for you to have some sort of logbook that you can refer back to at any stage. You will have to submit a final report on each of the questions to Moodle so it would be very useful if you could organise access to a digital camera in order to photograph your wiring setup etc.

Except where you are explicitly told otherwise, please do not copy any material from the instructions for the assignment into your reports.

Number each section/subsection of your report clearly. (If the instructions for the particular assignment are already numbered, then follow this numbering system in your report also.)

Graphs, diagrams, figures etc. must be labeled with a number and a descriptive title (e.g., "Figure 1: Breadboard Wiring Layout", "Graph 3: Clock Pulse Waveform" etc.). If a graph or figure is referenced in your text this should be done using its assigned number (e.g., "As shown in graph 6, the maximum voltage detected was ..." etc.).

Graphs if required should always be drawn on the graph paper and photographed or there are online charting tools that can be used to generate images. 

Both axes on a graph must be labeled with the quantity recorded (matching the lables in the corresponding data table, if any) and the specific units of measure (V, s, A, etc.).

Equipment:

The main equipment used in these labs consists of, your personal component kit that contains:

• Digital integrated circuits (ICs): Please handle carefully and try to avoid touching the legs with your fingers as the static electricity naturally present on your body can destroy them.

• A digital multimeter: you may need to measure specific voltage values. Again, if in any doubt about the use of the meters, please check with a tutor. Measuring current is the most likely way to damage a multimeter. If you measure a short-circuit current or a current that is too high it will blow an internal fuse that will have to be replaced. Please talk to the tutor if this happens.

• Connecting wires: You should have a prototyping breadboard that has connection wires. Use the shortest wires possible to make your connection and use the colours to describe different meanings. For example, use black wires to describe GND connections, red to describe +5V connections etc.

• Many miscellaneous components, such as resistors, capacitors, voltage regulators etc.

Breadboards:

Breadboards are what you use to assemble your experimental circuits. Each breadboard consists of two terminal strips and two bus strips. 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. Each terminal strip has 60 rows and 5 columns of contacts on each side of the centre gap. Each row of 5 contacts is a node.

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 on any given breadboard.

For the Digital electronics labs we will use only the 5V supply. Please take care to connect the 5V supply with the correct polarity; and not to connect the 9V battery directly to the bus strips: doing so may result in damage, including rapid over-heating, which may be dangerous to the people working on the experiment. Always double check all circuit connections before applying power.

Figure 1 The breadboard. The orange lines indicate connected holes.

Building the Circuits:

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:

• Disconnect the power to the breadboard before you build anything!

• Make sure the power is off before you build anything! (Have you checked?)

• Insert the chips you will be using into a breadboard. Point all the chips in the same direction with pin 1 at the lower-left corner. (Pin 1 is normally identified by a dot or a notch next to it on the chip package)

• Connect +5V and GND (0V) pins of each chip to the power and ground bus strips on the breadboard.

• Select a connection on your circuit 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.

• You should never connect the outputs of two separate gates directly together.

• You may connect any given signal to several gate inputs in parallel.

• Your final connections for each circuit should be between the power rails on your breadboard(s) and the output of the voltage regulator. Make sure to get the polarity right, and to connect only to the +5V supply. This is much easier if you consistently use color coding for your wiring (red and black for the +5V and GND power supply lines respectively; other colors for signals, as appropriate).

• Check all the connections, before you connect the power.

• Finally, connect the power. Watch for any sign of malfunction - e.g., burning, smoke, etc. If you notice such signs, at any time, disconnect the power immediately. Check your circuit again.

• When you connect the voltage regulator for the first time, measure the voltage on its output +5V supply rail, and verify that it is correct. 

• Always switch off the power again before starting to rewire or re-configure the circuit in any way.

• At the end of your work, collect your hook-up wires, ICs etc., and store them correctly.

Common Causes of Problems:

Very common causes of problems in these experiments include:

• Not connecting the ground and/or power pins for one or more ICs - Every chip needs power!!

• Connecting the power with the wrong polarity on one or more ICs.

• Not turning on the power supply(!).

• Leaving out wires.

• Plugging wires into the wrong holes.

• Connecting the outputs of two or more gates directly together.

• Modifying the circuit while the power is still on.

• Not pressing the ICs down properly into the board, or bending a leg when pressing the IC down.

Example Breadboard Implementation of a Logic Circuit:

Suppose you need to build a circuit to implement the Boolean function F = /(/A./B). Please note that the notation /X is used here to denote logical inversion (complementation, or applying the NOT operator). You should use this notation during the write-up of your laboratory experiments.

Fig 2. The complete designed and connected circuit

Place your ICs 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.