DC Circuits Lab

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DC Circuits Lab

• Professor Ahmadi
• ECE 002

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Objectives

• Constructing a Series Circuit
• Ohms Law Review
• Breadboard Overview
• DC Power Supply Review
• Measuring the D.C. Voltage in the Series Circuit
• Multimeter Overview

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Today we will build this series circuit

• Series Circuit From Lecture

• Determine the current
• Use Ohms Law
• V I x R
• 3V I x 1000 O
• Solve for I
• I3V / 1000 O 3milliAmps

R 1K O
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How to Build the Circuit

• 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 mini-grabber wires

R 1K O
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The Breadboard

• The breadboard is building circuits quickly
  without the need for soldering
• You can plug resistors and wires right into the
  board

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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

BRIDGE
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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

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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.

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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.

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Setting Up the DC Power Supply
Press this arrow to Select the desired digit
This is the digit we want to adjust

• 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.

Rotate this dial to alter the output value.
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Connecting the Power Supply to your Circuit

• 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 mini-grabbers to your
  circuit, press the Output On/Off to apply 3 Volts
  across your 1K resistor

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Measuring the Voltage Across the ResistorUsing
the Multimeter
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What is a Multimeter?

• A tool capable of measuring a variety of
  different quantities.
• Possible Measurements
• Current (Amperes)
• Resistance (Ohms)
• Voltage (Volts)

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How is the Multimeter different than the
Oscilloscope?
Oscilloscope
Multimeter

• Numerical Output Displayed
• Represents a complete signal with a single value.
• Measures voltage, current and resistance.

• Graphical Output Displayed
• Shows how a signal changes over time
• Many only display voltage

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Explanation of Controls

• Setting up the multimeter for various
  measurements.

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Taking measurements with the Multimeter

• First, we connect our wires.

• 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
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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
Power Button
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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 wouldnt want to choose 200mV (much
  too small) or 200V (much too large). Instead,
  the 2V selection is more suitable.

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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!!

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Building Verifying Series Circuit 2

• Resistors connected by only 1 terminal,
  back-to-back, are considered to be in series

R1 1KO

• Ohms Law States
• V(R1) 1.5mA x 1K O 1.5V
• V(R2) 1.5mA x 1K O 1.5V

R2 1KO

• We are now going to build the circuit, and verify
  the voltage drops

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Setting up the breadboard

• Turn off the 3V supply and disconnect the cables
• Disconnect the cables to the minigrabbers to the
  multimeter
• Obtain a 2nd 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 another row

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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

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Resistors in Parallel

• 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
• The current will split!
• It is now up to you to build this circuit and
  verify the voltages

R1 1K O
R2 1K O
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Including a Diode In the Circuit

• Well use LEDs (Light Emitting Diodes) for our
  circuits.

• Unlike resisters, 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).

R1 1KO
0V

• Note In some diodes, a stripe is used to
  indicate the cathode lead. Round diodes often
  have a flat side, indicating the cathode.

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Your Turn

• 1) Build the parallel circuit (in the last slide)
  and measure the voltage across it
• Using Ohms 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 Ohms law to determine the current through
  each resistor
• Show your TA
• 3) Rebuild the two resistor series circuit
• Change one of the 1K resistors to a 2K resistor
• Measure the voltage across each resistor
• Use Ohms law to determine the current through
  each resistor
• Show your TA

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Your Turn

• 4) Build a circuit with a diode in series with a
  1K resistor
• Using Ohms 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 Ohms law to determine the current through
  each resistor
• Show your TA
• 6) Dont forget the HW!