Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Introduction This PowerPoint is a companion to the videos in “Background / Resources / Multimeter Guide” It is recommended that you watch the videos for an animated explanation of this PowerPoint

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Overview In this presentation, you will learn: Continuity Using a multimeter to test continuity Reading direct current voltage using a multimeter Reading the voltage of a battery

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Continuity What is continuity? – Defined as: uninterrupted connection – The circuit below has continuity – The circuit has an uninterrupted connection with the battery Battery

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Continuity continued If the wire is cut, the circuit no longer has continuity and the light bulb is not lit Battery Missing segment of wire

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Continuity Testing How to perform a continuity test: Continuity testing is done with a multimeter Allows a technician to see whether or not a circuit is complete Checking for continuity can help you locate: – Broken wires – Defective switches – Loose connections

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 1 Move the selector switch to the continuity setting

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 2 Remove insulation from the ends of a piece of wire Touch the multimeter test probes to the wire, as shown If the wire is good, you will hear a tone from the multimeter, and the display will show all zeros

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 2 continued Note that polarity does not matter If you switch the probes of the multimeter, you should still hear a tone if the wire is good

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 3 Test the bumper switch by building the setup to the right If you press the bumper switch, you will hear a tone The tone means that the bumper switch is working Repeat this set of steps for the limit switch

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 3 continued Note that you can directly connect the probes to the proper pins of the bumper switch instead of using the breadboard You will see the same results

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Batteries and Continuity Continuity tests cannot be performed on batteries If you try to perform a continuity test on a battery, you will not harm the meter, but you will get incorrect readings Batteries should be removed before testing the continuity of any device

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Practice You can try continuity tests on: – Switches – Wires – Cables – Flashlight bulbs This will give you more experience with continuity testing Battery

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER DC Voltage Testing What is DC Voltage testing? – Reading the voltage of circuit elements, such as batteries and cells Why is this useful? – Weak or dead batteries will render your electronic device useless – DC voltage testing is a good first step in troubleshooting For more information on direct or alternating current, refer to “Overview / Guides / Note to the Student”

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 1 How to read DC voltage: Insert the red test wire into the red jack, as shown Do the same for the black wire

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 2 Rotate the multimeter’s selector switch to DC Volts The multimeter is now ready to read voltage from a device

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 3 Touch the multimeter probes to the ends of a AA battery Standard voltage for AA batteries is 1.5 V Does your display show this? What happens when you switch the multimeter probes?

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 3 continued If you switch the probes, your voltage reading will become negative What is polarity? – Having two oppositely charged poles, one positive and one negative – Batteries have polarity – On a multimeter: The black probe is negative The red probe is positive 1.5 V Battery + - Multimeter Reading: Negative probePositive probe V Battery + - Multimeter Reading: Positive probeNegative probe

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 4 Touch the probes of the multimeter to a 7.2 V battery Do this by connecting the probe tips to the connector pins inside the plug as shown What is the multimeter’s reading?

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 5 Remove the batteries from your radio control transmitter Lay them out end to end, as shown Make sure the negative terminals only touch positive terminals

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 5 continued Connect the meter as shown Make sure that the red probe is touching the positive terminal of the top battery Make sure that the black probe is touching the negative terminal of the bottom battery What is the total voltage of these 8 batteries?

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 5 continued When batteries are connected together like below, their voltages add together These batteries are “in series” Voltage of 1 AA battery = 1.5 V Number of AA batteries = 8 Total voltage of 8 AA batteries in series: 1.5 V V V V V V V V = 12 V 1.5 V x 8 = 12 V

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 6 Place the batteries back in the radio control transmitter Place the probes as shown Observe the voltage reading What do you expect it to be?

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 6 continued Now, place the probes differently, as shown at right What voltage reading did you get?

Vex 1.0 © Carnegie Mellon Robotics Academy Inc. MULTIMETER Step 6 continued Continue to move the black test probe, as shown Do the values you read from the multimeter make sense?