ECE Undergraduate Laboratory
FED 101 - Fundamentals of Engineering Design

FED 101 - Fundamentals of Engineering Design

Lab 1: Resistors
Resistor Circuit, Series, Parallel

In this experiment you will examine resistors, as a single component, in series or in parallel, and build and analyze a simple resistor circuit. You will also become acquainted with the digital multimeter that you will be using throughout this course.

Background material for this experiment can be found in Chapter 2 of this manual


PARTS LIST:


Background - Protoboards

To perform this experiment, students will need to become familiar with the protoboard and the logic probe they will use. Both are described in this section.

We can construct a circuit using digital logic chips, but we need a surface to secure the chips and wires that comprise the circuit. This is the function of the protoboard. Chips and wires are plugged into the protoboard and can be rearranged easily as the design is modified. (Final circuits are wired on breadboards. Protoboards are typically used during the design of prototypes, hence its name.) A typical protoboard is shown in Figure 1.1


Figure  1.1
Figure 1.1: A typical protoboard

The terminals on the side of the protoboard are used to connect the power supply (Vcc and Gnd) to the circuit. One pair of cables connects the power supply to these terminals, and wires connect the terminals to the protoboards.


Figure  1.2
Figure 1.2: A protoboard wired to have efficient access to power and ground.

If you are going to use a single power supply, then get into the habit of connecting all the blue lines to each other and to ground (see bottom left and top left connections in Figure L1.2), and all the red lines to each other and to Vcc. This gives you the ability to connect components to Vcc and ground with shorter wires, making the circuit easier to debug. Even though the final version of any implementation is supposed to utilize the shortest wires for any connection, it is acceptable if the wires are not optimized at the beginning for as long as the circuit does not look like a jungle of wires.

The main protoboard surface consists of a grid of holes. The pins of the chips in a circuit are plugged into these holes; for reasons that will be explored shortly, the chips must straddle the relatively large channels, or gutters, separating columns of holes. The chips cannot be placed in the top or bottom rows. These special power rows are reserved for Vcc and Gnd.

The protoboard has connections embedded within its structure so that certain holes are always connected to each other. As a result, wires and pins plugged in to connected holes are also connected. This greatly simplifies the task of wiring up circuits. Any hole is connected to all other holes in the same row between the same two channels; this is illustrated in Figure L1.3. When dealing with integrated circuit chips later in the course, you will see that this is the reason that chips must straddle the gutters, to avoid inadvertently connecting pins on the same chip. The power columns are also connected, but in a different way. Here, holes are connected to other holes in the same long rows. Designers can connect wires from the two terminals connected to Vcc and Gnd to these rows, and then connect wires from these columns to the power pins of each chip. Note that the power rows are divided in two separate halves (not connected) in the middle of the protoboard; watch out for this when wiring up your circuits for this and future experiments. They also are not connected to the power posts; you have to do it with wires


Figure  1.3
Figure 1.3: Protoboard internal connections. Connect two top horizontal rows (detail shown on the right) to the positive (red) and negative (black) power terminals.

Basic rule of wiring circuits

DO NOT MAKE CONNECTIONS WHEN THE POWER IS ON – YOU CAN DAMAGE BOTH THE CIRCUIT PARTS AND THE PROTOBOARD.



Part 1: Resistor Measurements

Using the multimeter, measure the resistance of three different resistors. Make a table showing a nominal value for each resistor (the value indicated by its color bands) and its measured value. In the last column of the table indicate if a resistor value is within its tolerance specification.


Part 2: One Resistor Circuit


Wire up the circuit shown below. Using the multimeter, measure the voltage across the resistor. Also measure the current flowing through the resistor. Using Ohm’s Law, verify that your measurements are valid for this circuit. Note that you have to set your multimeter to ammeter for measuring the current. In addition, the ammeter has to be inserted in series with the component whose current is of interest. The way the components are connected together, the current read by the multimeter is the current that exits the positive terminal of the battery (red connector) and enters the positive terminal (red connector) of the ammeter (current flowing clockwise).

Make clear in your notes which are measured and which are calculated values. In your calculations, always use the measured value of the various resistances that may be involved in a circuit.


Figure  1.4
Figure 1.4: Simple 1-resistor circuit, voltage and current

Note: Do not worry if you have trouble setting the voltage at exactly 5.00 V, values such as 5.07 or 4.85 are close enough. It is unlikely that your resistor will have an exact value of 1.00 kΩ. No problem: measure it with the multimeter (on a resistance scale) and in the calculations use the real measured values of the voltage and resistance, not the nominal values shown in the figure.


Show the record of the experiment in the laboratory notebook at the end of the class.


Part 3 – Series and Parallel Resistive Circuits


If you use a digital ohmmeter, you will rarely have any difficulty reading the actual values of resistances because the digital meter has a very high internal impedance. However, even with a digital meter, if you experiment with a large resistance (like 1 MΩ), you will find out that if your hands are touching both terminals while executing the measurement, the value read will be different from the actual value because your body does not have an infinite resistance, and hence you are measuring the resistance of the resistor in parallel with your body.