EXPERIMENT 1 PRELIMINARY MATERIAL

Transcription

1 EXPERIMENT 1 PRELIMINARY MATERIAL BREADBOARD A solderless breadboard, like the basic model in Figure 1, consists of a series of square holes, and those columns of holes are connected to each other via metal strips. Sliding wires through the holes result in connecting it with the metal strip inside.

2 Each column (1 to 30) is shorted (interconnected) electrically (A to E and separately F to J). Any hand-drawn circuit can be designed on the board, provided it fits in the board. Figure 2 shows how the columns in a breadboard are connected electrically. Figure 2 also shows the long rows of shorted holes at the very top and bottom of the solderless breadboard. These rows are mainly designed to distribute power and ground to the circuit. Most boards have two rows at the top and bottom. In some boards, those rows are connected to each other electrically (i.e., two ground rows are interconnected and power rows are interconnected separately), but on other boards, each row is electrically isolated from the other (e.g., top ground row is not connected to bottom ground row). Rather than assuming they are interconnected, it is wise to check two rows by connecting them to each other via multimeter probes. Low resistance shows the two rows are interconnected (shorted), while a very large resistance value shows the two rows are not connected (open).

3 MULTIMETER The multimeter, also called an ampere-volt-ohm meter (or avometer), is the basic tool for anyone working in electronics. A fairly typical modern multimeter can be seen in Figure 3. A multimeter can be used to take a variety of electrical measurements, hence the term multi. With a multimeter: - AC/DC voltages (Volt), - Resistance (Ohm), - Current (Ampere), - Continuity (whether a circuit is broken or not) can be measured. Depending on the model, values from capacitors, diodes, and transistors can also be measured. All multimeters come with a pair of test leads (i.e., probes), one black and one red.

4 Black denotes the negative terminal (ground), while red denotes the positive terminal. To check the voltage difference between node A and node B (i.e., A B), one should connect red probe to node A and black probe to node B. Measurement of current using a multimeter might be a little tricky. The multimeter should be connected in series with the wire whose current will be observed while the circuit is powered. OSCILLOSCOPE An oscilloscope is a laboratory instrument commonly used to display and analyze the waveform of electronic signals. In effect, the device draws a graph of the instantaneous signal voltage as a function of time. A typical oscilloscope can display alternating current (AC) or pulsating direct current (DC) waveforms with a frequency as low as approximately 1 Hertz (Hz) or as high as several Megahertz (MHz). High-end oscilloscopes can display signals with frequencies up to several Gigahertz (GHz). The display is broken up into so-called horizontal divisions and vertical divisions. Time is displayed from left to right on the horizontal scale. Instantaneous voltage appears on the vertical scale. Figure 4 Simple waveforms Figure 4 shows two common waveforms as they might appear when displayed on an oscilloscope screen. The signal on the top is a sine wave; the signal on the bottom is a ramp

5 wave. It is apparent from this display that both signals have the same, or nearly the same, frequency. They also have approximately the same peak-to-peak amplitude. Suppose the horizontal sweep rate in this instance is 1 µs/div. Then these waves both complete a full cycle every 2 µs, so their frequencies are both approximately 0.5 MHz or 500 kilohertz (khz). If the vertical deflection is set for, say, 0.5 mv/div, then these waves both have peak-to-peak amplitudes of approximately 2 mv. Initial steps while using an oscilloscope Turn power on: This may appear obvious. Usually the switch will be labeled "Power" or "Line". Wait for oscilloscope display to appear: Although many oscilloscopes these days have semiconductor based displays, many of the older ones still use cathode ray tubes (CRTs), and these take a short while to warm up before the display appears. Even modern semiconductor ones often need time for their electronics to "boot-up". It is therefore often necessary to wait a minute or so before the oscilloscope powers on. Find the trace: Once the oscilloscope is ready, it is necessary to find the trace. Often it will be visible, but before any other waveforms can be seen, this is the first step. Typically the trigger can be set to the center and the hold-off turned fully counter-clockwise. Also set the horizontal and vertical position controls to the center if they are not already there. Usually the trace will become visible. If not, the "beamfinder" button can be pressed and this will locate the trace. Set the gain control: The next step is to set the horizontal gain control. This should be set so that the expected trace will nearly fill the vertical screen. If the waveform is expected to be 8 Volts peak to peak, and the calibrated section of the screen is 10 cm high, then set the gain so that it is 1 Volt / cm. This way, the waveform will occupy 8 cm, almost filling the screen. Set the timebase speed: It is also necessary to set the timebase speed on the oscilloscope. The actual setting will depend on what needs to be seen. Typically, if a waveform has a period of 10 ms and the screen has a width of 12 cm, then a timebase speed of 1 ms per cm or division would be chosen.

6 Apply the signal: With the controls set approximately correctly, the signal can be applied and an image should be seen. Adjust the trigger: In this step, it is necessary to adjust the trigger level and whether it triggers on the positive or negative going edge. The trigger level control will be able to control where on the waveform the timebase is triggered and hence the trace starts on the waveform. The choice of whether it triggers on the positive or negative going edge may also be important. These should be adjusted to give the required image. Adjust the controls for the best image: With a stable waveform in place, the vertical gain and timebase controls can be readjusted to give the required image. FUNCTION GENERATOR A function generator is a device that can produce various patterns of voltage at a variety of frequencies and amplitudes. It is used to test the response of circuits to common input signals. The electrical leads from the device are attached to the ground and signal input terminals of the device under test. Features and controls: Most function generators allow the user to choose the shape of the output from a small number of options: Square wave - The signal goes directly from high to low voltage. Sine wave - The signal curves like a sinusoid from high to low voltage. Triangle wave - The signal goes from high to low voltage at a fixed rate (slope). The amplitude control on a function generator varies the voltage difference between the high and low voltage values of the output signal. The direct current (DC) offset control on a function generator varies the average voltage of a signal relative to the ground.

7 The frequency control of a function generator controls the rate at which output signal oscillates. On some function generators, the frequency control is a combination of different controls. One set of controls chooses the broad frequency range (order of magnitude) and the other selects the precise frequency. This allows the function generator to handle the enormous variation in frequency scale needed for signals. The duty cycle of a signal refers to the ratio of high voltage to low voltage time in a square wave signal. How to use a function generator: After powering on the function generator, the output signal needs to be configured to the desired shape. Typically, this means connecting the signal and ground leads to an oscilloscope to check the controls. Adjust the function generator until the output signal is correct, then attach the signal and ground leads from the function generator to the input and ground of the device under test.

8 EXPERIMENT 1 LAB WORK Objective: The two purposes of this experiment are to learn how to implement digital circuits on a breadboard and to understand how common gates (AND, OR, NOT) work by observing that the following Boolean Algebra tautology (i.e., fact) holds: Tools: X + X' Y = X + Y Breadboard Wires DC Power Supply Multimeter 7408 (AND gate) 7432 (OR gate) 7404 (NOT gate) Procedure: 1. Build the following circuit on the Breadboard. (Vcc = 5V, Gnd = Ground) 2. Fill the truth table for the measured F2. (Logic 0 0V, Logic 1 5V)

9 3. Build the following circuit on the Breadboard. (Vcc = 5V and Gnd = Ground, also keep in mind that only bold dots indicate short circuit. Other wire intersections are just bypasses.) 4. Fill the truth table for the measured F1. (Logic 0 0V, Logic 1 5V)

10 Pin Numbers for AND, OR, and NOT Gates: For more information you can consult datasheets: AND Gate OR Gate NOT Gate