Download Lab2 protocol - Basic Electric Measurements

Freshmen Engineering Clinic II
EC
2
Polikar
Spring 2002 - Robi Polikar
ECE 0901.102.03
Freshmen Engineering Clinic II
Week 4
Lab Date: 02/12/2002
Due Date: 02/19/2002
This week we are going to walk in Ohm’s footsteps. Of course, we will have access to little better test
equipment than he had, but hey…that’s life !
But, first things first…From now on, we will start using sophisticated electronic test equipment. The first
couple of weeks, you will need to show me your circuit before you turn the power on. No joking around with
these equipment, particularly no scaring other team members by touching them with test leads and making
electrocution sounds. It is NOT funny, nor will it be tolerated. Safety first! If you see someone engaged in
unsafe practices, remind him/her with our previously determined safety gesture. Second, when you are done,
you MUST put everything back in its place. Do not leave test leads, electronic components, etc. on test
benches. Note that this is a group responsibility. You will not be reminded again, and if you are caught – the
entire team will get a zero for that week’s lab! Please do not let this happen to you.
First, let’s meet our new friends:
Breadboard: The breadboard is used to build test circuits without using a printed circuit board (PCB). A
circuit is transferred onto a PCB only after it is tested and validated. Until then all tests are done on the
breadboard. Breadboards allow us to build circuits easily without requiring soldering. The breadboard has
many strips of metal (copper usually), which run underneath the board. The metal strips are laid out as shown
below. These strips connect the holes on the top of the board. This makes it easy to connect components
together to build circuits. To use the breadboard, the legs of components are placed in the holes (the
sockets). The holes are made so that they will hold the component in place. Each hole is connected to one of
the metal strips running underneath the board. Note that all holes along a given metal strip are connected to
each other, hence they are “shorted”.
Metal strips
Holes for
connecting the
components
underneath the
breadboard
Digital Multimeter (DMM): This is the device we will use most often. It is capable of making current,
voltage, resistance, frequency and temperature measurements, among others.
Use these two connections to make voltage or
resistance measurements. Remember to click
DCV (for voltage) and 2 for resistance
measurements, and connect the leads in parallel.
Why? (Explain in your report)
Use these two connections to make current
measurements. Remember to click DCA, and
connect the leads in series on the path of current
flow. Why? (Explain in your report)
Freshmen Engineering Clinic II
Spring 2002 - Robi Polikar
Power Supply: This power supply will provide us with up to 25V of DC power. It can be used in two modes:
Up to 6V or up to 25 V. You must have your instructor check your circuit before you apply the power on
(Power On/Off key – not on/off switch).
Power
on/off key
Use these two
connectors for
up to 25 V
Use these two
connectors for
up to 6 V
Cables, Components and leads: You will find a variety of cables, connectors, leads and
components in the lab. Make sure that you know, particularly what component is what before you
use them. Do not mix up resistors with capacitors, or transistors with variable resistors.
In today’s lab:
1. We will first repeat the Ohm’s experiment to determine value of a single resistor. Grab a
resistor, with a value between 1k and 10k, and build the following circuit on the
breadboard. Apply 1V to the circuit and measure the current flowing through the circuit.
Gradually increase the voltage in steps of 0.1V up to 6V. Note the current values. Draw a
current vs. voltage graph by logging your values into an Excel sheet (voltage on the vertical
axis). What do you observe? How would you obtain the resistor’s value from this graph?
Check your result by measuring the actual resistance using the DMM (never measure
resistance when the power is applied). Were you right?
_
I
V
R
+
2. Now do the same experiment with the following circuit to find the effective resistor between
points A and B. Confirm your results by measuring the effective resistance using a DMM, as
well as computing it by hand. You may pick the resistor values in any way you want.
Identical R values will make manual computations slightly easier. Do pick, however,
standard resistor values, such as those you will find in the lab.
_
V
A
R2
R4
R3
R1
R6
R5
+
B
R10
R9
R8
R7
Freshmen Engineering Clinic II
Spring 2002 - Robi Polikar
3. And, repeat Question 2 for the following circuit. Can you find the solution by hand? Ignore
the currents drawn for this question.
i1
_
i7
i5
i3
A
V
i2
+
i6
i4
B
i8
i10
i9
i11
4. Now let’s look at those currents. In fact, look at them closely… Or better yet, measure them.
Be careful how you measure the currents! Remember that the ammeter (or the DMM used in
ammeter mode) must be connected in series with the current flow. Measure all currents
indicated i1 through i11. Examine the values you obtain very carefully. Do you notice any
connection between these currents?
5. How about the voltages? Measure enough many voltages – potential differences or voltage
drops – on the nodes (you do not need to this between every pair of nodes) to establish a
connection between these voltages.
6. As a reading homework, find out what Kirchoff’s current and voltage laws are (KCL and
KVL, respectively). Explain, if and how your findings validate the KCL and KVL.
7. Obtain a regular diode and a light emitting diode (LED) from the lab supply, and build the
following circuits. Use the LED first. Use identical R=1kohm values for all resistances. First,
for the circuit on the left: Apply V=6V and measure voltage differences among R1, R2 and
D1. Now gradually reduce V by steps of 0.5V. Measure the voltage differences again. What
do you observe? As you approach 2V, reduce steps to 0.1V. Did you observe anything
unusual? Now, reverse the polarity of the diode, and repeat your experiment? What did you
notice? Based on this observation, what can you say about diodes? Now do the same
experiment using the circuit on the right. The dotted lines show that you should make the
measurements with and without these components in the circuit.
_
A
R1
V
_
D1
A
R1
V
+
D1
R3
+
B
R2
Diode
B
R2
Team building exercise of the week: Grab a “cable bunch” from the instructor, which are
specially prepared by your instructor for this very activity. You are to find two ends of at
least two strings of wires in that bunch. The first team to find to such wires will get an
additional 10% on this week’s lab. Have fun!
Short
circuit