Professor Ahmadi
ECE 002
George Washington University
1

Objectives
 Constructing a Series Circuit
 Ohm’s Law Review
 Breadboard Overview
 DC Power Supply Review
 Measuring the D.C. Voltage in the Series Circuit
 Multimeter Overview
George Washington University
2

I = ? Amps
 Series Circuit From Lecture
 Determine the current
3V R = 1K Ω
 Use Ohm’s Law:
V =
I x
R
3V =
I x
1000
Ω
Solve for I :
I
=3V / 1000 Ω = 3milliAmps
0V
3
George Washington University

I = 3mA
3V R = 1K Ω
 We need 5 components
1) A 1K Ohm Resistor (Ask your
GTA for these materials)
2) Breadboard
3) DC Voltage Source
4) 2 sets of Banana Clip to minigrabber wires
4
0V
George Washington University

The Breadboard
 The breadboard is building circuits quickly without the need for soldering
 You can plug resistors and wires right into the board
5
George Washington University

The Breadboard
 The 5 holes in each row are wired together underneath the breadboard
 The rows themselves are not wired together
 The rows do not connect over the bridge
 The columns between the blue and red bars are connected vertically
 We typically use these as ‘power rails’
 The left side we use for positive voltage
 The right side we use for negative voltage
6
George Washington University

Setting up the breadboard
 Plug 1 end of the 1K resistor in the top row, on the left side of the bridge
 Plug the other end of the resistor into the top row, on the right side of the bridge
7
George Washington University

Setting Up the DC Power Supply
 This DC Power supply is capable of generating voltages from -25V to 25V.
 For this lab, we will be using the 6V supply terminals.
 First, press the Power
Button to turn it on.
8

Setting Up the DC Power Supply
 Press Output On/Off once to turn on the output.
 Press the +6V button to tell the power supply that we want to alter the output from the 6V terminals.
 Once done, your screen should look the same as it does on this slide.
9

10
Setting Up the DC Power Supply
 Use the dial to increase the display value to 3 volts as shown.
 Note: You can safely ignore the value of the right most digit for this experiment.
 Once you have reached 3V,
Press Output On/Off once to turn the output OFF while you hook up the circuit.
This is the digit we want to adjust
Press this arrow to
Select the desired digit
Rotate this dial to alter the output value.

 Plug the ‘banana’ end of your cables into the 6V terminals of your power supply
 Connect the mini-grabber ends of the cables around your 1K resistor on the breadboard
 After attaching the minigrabbers to your circuit, press the Output On/Off to apply 3 Volts across your 1K resistor
11

12
George Washington University

What is a Multimeter?
 A tool capable of measuring a variety of different quantities.
 Possible Measurements
 Current (Amperes)
 Resistance (Ohms)
 Voltage (Volts)
13
George Washington University

How is the Multimeter different than the Oscilloscope?
Multimeter
 Numerical Output Displayed
 Represents a complete signal with a single value.
 Measures voltage, current and resistance.
Oscilloscope
 Graphical Output Displayed
 Shows how a signal changes over time
 Many only display voltage
14
George Washington University

Setting up the multimeter for various measurements.
George Washington University
15

Taking measurements with the
Multimeter
 One wire is always connected to the black terminal. This is called the common terminal.
 The red terminal is used when measuring voltage, resistance and small currents.
 The white terminal is used when measuring large currents.
TO DO : Using another set of banana to mini-grabber cables, connect the banana end to the red & black terminals
George Washington University
16

Taking measurements with the
Multimeter
 Next, we turn it on and select the item to measure.
 Choose from:
 Current
 Resistance
 Voltage
TO DO : Since we want to measure the voltage across our 1K ohm resistor, press the Voltage button
17
Power
Button
George Washington University

Taking measurements with the
Multimeter
 Now, we select our scale.
 Either select a scale appropriate for your measurement or choose AUTO and let the multimeter select the appropriate scale for you.
 Measuring the voltage from across the 1K resistor (~3V), you wouldn’t want to choose 200mV (much too small) or 200V (much too large).
Instead, the 2V selection is more suitable.
18
George Washington University

Taking measurements with the
Multimeter
 While your circuit is attached to the power supply…
 Attach the minigrabber end around the 1K resistor
 Press the “POWER” button on the multimeter and take a reading!!
19
George Washington University

20
R1 = 1K Ω
3V R2 = 1K Ω
 Resistors connected by only
1 terminal, back-to-back, are considered to be in
‘series’
 Ohm’s Law States:
V(R1) = 1.5mA x 1K Ω = 1.5V
V(R2) = 1.5mA x 1K Ω = 1.5V
 We are now going to build the circuit, and verify the voltage drops…
0V
George Washington University

Setting up the breadboard
 Turn off the 3V supply and disconnect the cables
 Disconnect the cables to the minigrabbers to the multimeter
 Obtain a 2 nd 1K resistor
 Plug one end of the resistor into a hole in the same row as the end of the other resistor
 Plug the other end into a hole in
21

Taking measurements with the
Multimeter
 Set the Power Supply to 3V
 Attach the power supply leads as follows
 Measure the voltage across each resistor with the multimeter
22
George Washington University

23
3V
 Resistors connected at 2 terminals, sharing the same node on each side, are considered to be in
‘parallel’
 The voltage is the same on both branches of the circuit
R1 = 1K Ω
0V
 The current will split!
R2 = 1K Ω
 It is now up to you to build this circuit and verify the voltages
George Washington University

24
 We’ll use LEDs (Light
Emitting Diodes) for our circuits.
3V
 Unlike resistors, the two diode leads (wires) must be connected in the correct way.
 The longer lead (anode) should be connect so that current flows through it and to the shorter lead (cathode).
0V
 Note: In some diodes, a stripe is used to indicate the cathode lead. Round diodes often have a flat side, indicating the cathode.
George Washington University

Your Turn
1) Build the parallel circuit (in slide 23) and measure the voltage across each resistor
 Using Ohm’s Law, what is the current through each resistor?
 What is the total current in the circuit?
 Show your TA your circuit, measurements, and calculations
2) In your parallel circuit, change one of the 1K resistors to a 2K resistor
 Measure the voltage across each resistor
 Use Ohm’s law to determine the current through each resistor
 Show your TA…
3) Build the two resistor series circuit (slide 20)…
 Swap the second of the 1K resistors for a 2K resistor
 Measure the voltage across each resistor
 Use Ohm’s law to determine the current through each resistor
 Show your TA…
George Washington University
25

Your Turn
4) Build a circuit with a diode in series with a 1K resistor
 Using Ohm’s Law, what is the current through the resistor?
 What is the total current in the circuit?
 Show your TA your circuit, measurements, and calculations
 Reverse the anode and cathode connections of the diode and observe the results.
5) Build a circuit with a diode in series with 2 parallel 1K resistors
 Measure the voltage across each resistor
 Use Ohm’s law to determine the current through each resistor
 Show your TA…
6) Don’t forget the HW!
26
George Washington University