George Washington University DC Circuits Lab Professor Ahmadi ECE 002

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

George Washington University How to Build the Circuit We need 5 components 3V 0V R = 1K Ω 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 I = 3mA

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

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 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

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

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. George Washington University

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. George Washington University

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. George Washington University This is the digit we want to adjust Press this arrow to Select the desired digit Rotate this dial to alter the output value.

George Washington University 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 George Washington University

Measuring the Voltage Across the Resistor…Using the Multimeter

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)

George Washington University How is the Multimeter different than the Oscilloscope? 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 Multimeter Oscilloscope

George Washington University Explanation of Controls Setting up the multimeter for various measurements.

George Washington University 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

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

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!!

George Washington University Building & Verifying Series Circuit #2 Resistors connected by only 1 terminal, back-to-back, are considered to be in ‘series’ 3V R2 = 1K Ω 0V R1 = 1K Ω 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…

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 another row

George Washington University 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

George Washington University Resistors in Parallel Resistors connected at 2 terminals, sharing the same node on each side, are considered to be in ‘parallel’ 3V 0V R1 = 1K Ω 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 R2 = 1K Ω

George Washington University Including a Diode In the Circuit We’ll use LEDs (Light Emitting Diodes) for our circuits. 3V R1 = 1K Ω 0V 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). 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 the last slide) and measure the voltage across it 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) Rebuild the two resistor series 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…

George Washington University 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!