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To familiarize students with the basis of safety, lab procedures, and the equipment to be used throughout the course.
The careless use of electricity can have two results. It can hurt you. It can hurt equipment. Obviously, you want to avoid hurting anything.
To project yourself, always treat electricity with respect. Don't handle "hot" lead wires. Don't leave wire dangling about in space. An old rule of thumb is to keep one hand in your pocket at all times. This hopefully prevents the flow of electricity from one hand to another, potentially causing the heart to stop. Keeping one hand in your pocket also causes cramps, and decreases efficiency, so no one does it. But keep in mind that when you touch a wire that is electrified, the electricity will always want to flow, and it is to your advantage to keep it from flowing through you. Don't hold electrified wire, and make sure that no part of your body inadvertently comes into contact with a wire.
To protect equipment, make sure that all of the hookups between power supplies, oscilloscopes, volt-ohm meters, light emitting diodes (LED's), protoboards, chips, etc., are as you want them to be. Double check all wiring prior to turning on the power. One way to destroy an Integrated Circuit (I.C.) is to reverse power leads. You can tell because the abused I.C. will start smoking or will get so hot you cannot touch it. Then throw away the I.C.
When probing a circuit with a test lead, make absolutely certain that you are making contact with the exact points you wish to test, and ONLY those points.
When using a particular piece of test equipment, understand the limitations of the equipment. Don't try to use it to test something it wasn't designed to test. Read the manual.
In summary, the way to keep yourself and the equipment from being damaged is to do everything slowly, cautiously, and carefully.
In order to make your experiments go easier, there are some procedures which should be followed. Most are common sense.
1.Before wiring a circuit, a circuit diagram should be drawn and simulated. This diagram should include pin numbers, and as each connection is wired, the connection should be checked off. For example:
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Without some system like this, it is very easy to forget which gate is which within a system. If you don't have a properly labeled circuit diagram prior to the beginning of lab, your instructor will give a 0 for lab performance.
2.While siring, rewiring, etc. turn off the power. This prevents the application of power to the circuit in unwanted places. Violation of this rule will result in decreased lab performance grades.
3.Avoid messy "rat's nest" wiring. It is almost impossible to trouble-shoot a messy wiring job. It is also hard to make changes to a messy board. Keep lead wires as short as possible, band make neat, flat bends. Try not to wire over the top of I.C.'s.
4.Wire the power leads of chips first, and use a color scheme if possible. Traditionally:
RED = +5 Volts BLACK = Ground
You can expand on this, e.g. - use yellow wires for inputs and green for outputs. This makes trouble-shooting much easier.
5.Wire circuits carefully. It is easier to wire it right than to spend hours tracking down an error. Make certain fragile leads are not bent excessively. 6.Handle equipment carefully. Don't drop anything. Put all components back where they are suppose to be. Observe polarity markings on equipment and components.
7.Before leaving the lab, check that your bench position is neat and orderly. Report any defective equipment to the instructor. Turn off all equipment, and make sure the bench power is off. Check the floor for wires.
The proper care of the equipment used in this lab is essential. If handled improperly, many of the devices used to perform the experiments will give erroneous readings or fail to operate altogether.
1.Protoboard
Your kit includes a plastic board used to wire together electric circuits. This is called a breadboard or a protoboard, since it is used to prototype circuits. The top view is shown in Figure 1.
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Special care is needed in using the protoboard. If a wire which is too large is forced into one of the holes, that particular hole may be damaged. As a result, the next time the protoboard is used and a wire is inserted into the damaged hole, the wire may not make contact with the internal connection strip and the circuit will not operate. Even more aggravating the wire can make contact only part of the time. This is called an intermittent fault. Since the circuit will operate correctly part of the time, and then mysteriously fail, this type of fault is very hard to find. A good rule to follow is - if the wire doesn't go in easily, find another wire. Pay particular attention to components such as resistors, capacitors - etc., since many have lead with diameters which allow insertion into the protoboard, but still cause damage.
You will have to stop wire leads which you will be using to interconnect circuits on your protoboards. The proper way to do this is to use a pair of wire cutters to carefully strip ¼" of insulation off of each end of the wire, taking care not to nick the copper wire. If you take more off than ¼" of insulation, you risk having wire exposed above the protoboard, which can cause shorts. If you cut less that ¼" of insulation, the wire may not make a connection to the internal connection strip. It also helps to cut the ends of the wire at an angle, which produces a point on the end of the wire. The wire will then slide into the protoboard easier. To avoid damage, do not insert wires too far.
2.Digi-Designer
You will be using the Digi-Designer during this lab. Each Digi-Designer has a protoboard in the middle. It is recommended that you place your protoboard on top of the one that is connected to the Designer. This way, you can use all of the functions provided by the Designer, and still be able to pick up your protoboard when the lab is finished with all connections intact. Also, you should prewire the circuit called for by each lab in order to save valuable lab time.
Some of the features of the Digi-Designer are:
A. ON-OFF switch - used to turn the power to the Digi-Designer on and off.
B.LAMP MONITORS - use LED's to indicate ground (light off) or +5V (light on). You can insert small wires into the tie points of the LED's and then insert the other end into a specific point on the protoboard. The tie points are connected to the LED's internally, as shown by the line on the box.
C.CLOCK - is a device which causes the tie points connected to it to alternate between +5V and ground at a rate by the rotary switch.
D.BANANA PLUGS - are the two jacks directly below the clock used ton convert between banana jack leads and tie points, and then to the protoboard.
E.+5V AND GRD - provide +5V and GRD to the tie points associated with them. Thus, if you connect a wire to one of the +5V tie points and also to the top row of holes on the protoboard, all of the top row will be energized at +5V.
F.LOGIC SWITCHES - these switches are used to provide either +5V or GRD to the associated tie points. You could move a wire between +5V and GRD to provide the same function, but it is much easier to use the switches when a lot of changes are going to be required.
G.PULSER - is used to provide a single pulse to a tie point. This pulse can be described as a +5V, GRD, +5V sequence (or vice-versa) on a wire. You could do the same thing by moving a switch (described above) from one position to the other and then back. However, the switch is a mechanical device and does not make each transition smoothly. The switch actually "bounces" on its contacts causing a series of pulses. The PULSERS perform the same function electrically, and are, therefore, called "de-bounced".
The Digi-Designer is a powerful (and expensive) design aid. Do not abuse it. Any questions you may have should be directed to the instructor.
3.Integrated Circuits (I.C.'s)
The I.C.'s supplied with the kit are used in a variety of experiments. Each looks like:
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The 16 pin I.C.'s supplied in the kit look like:
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SPECIAL CAUTION should be taken when inserting and removing I.C.'s from the protoboard. When shipped from the factory, the leads (legs) of the I.C.'s are slightly bent apart. They do this to aid in machine insertion. It is necessary to straighten the legs prior to insertion into the protoboards. This can be done easily by flattening the legs on a table top. Ask you instructor to show you. When you remove a chip (I.C.) from the protoboard, it is VERY EASY TO BEND the legs by not exercising caution. You should use the tip of a mechanical pencil to gently pry up the legs on each end of the chip. Again, ask your instructor to show you. Usually, if a leg is bent twice, it breaks off, and the I.C. is ruined. BE CAREFUL. Those I.C. legs are sharp, and it is easy to impale yourself if you try to remove them improperly.
Each report should, as a minimum, include:
Failure to include these lab sections will result in a reduced report grade.
The labs you are going to perform are fun! Take your time. Ask lots of questions. Understand everything that an experiment can show you. Try variations of circuits. The amount of information you learn from these labs is directly proportional to the amount of thought and effort you put into them. We would like to expand and improve this write-up. Please provide your comments and suggestions.
