This experiment introduces the Analog Discovery's™ Voltmeter instrument.
Voltmeters are used to measure voltage differences in a circuit. Since
voltages are a difference in electrical potential energy at two different points
in a circuit, voltmeters generally have two terminals, or leads.
When the leads are connected to two different points in a circuit, the voltmeter
displays the voltage difference between the two points.
Voltages are often categorized as being either constant or time-varying. Constant
voltages are often referred to as “DC” voltages (DC stands for
direct current, but DC has come to be used to describe any signal which
doesn't change with time). Time-varying voltages are often called
“AC” voltages, where AC stands for alternating current. The
Voltmeter instrument on the Analog Discovery can be used for measuring both DC and
AC voltages, but we will only be using it to measure DC voltages in this
Before you begin, you should:
Be able to use the Voltage
Instrument on the Analog Discovery to apply ±5V relative to the
Analog Discovery's ground.
Be able to state how the reference voltage polarity and connection of
voltmeter terminals are related to the sign of the measured voltage.
Be able to identify the voltmeter instrument terminals on the Analog
Discovery and also state the voltage polarity sign convention associated with
After you're done, you should:
Be able to use the Analog Discovery Voltmeter instrument to measure
If you have completed the Voltage
Instrument project and your circuit is still intact,
feel free to skip ahead to complete Part C of Steps 1 and 2
in this exercise.
Step 1: Understanding the Circuit
A. Circuit Schematic
Use V+ to apply 5V voltage across the LED to light it up.
The resistor limits the current.
To measure the voltage V, connect 1+ to the LED anode and 1-
to the LED cathode.
B. Create Basic Circuit
Connect V+ (red wire) to the 100Ω resistor.
Connect the 100Ω resistor to the LED anode.
Connect ground (,
black wire) to the cathode of the LED.
C. Voltage Measurement Connections
Connect 1+ (orange wire) to the diode's anode.
Connect 1- (orange and white striped wire) to the diode's cathode.
Step 2: Set up Instruments
A. Open Voltage Instrument
Return to the WaveForms™ main window.
Click on the Voltage icon to open the Power Supplies
B. Turn on Power
The LED should light up!
C. Open Voltmeter Instrument
Open WaveForms to view main window.
Click on the More Instruments dropdown menu to open the
Step 3: Experiment
A. Voltmeter Instrument
The voltage across the diode will be displayed under
Test Your Knowledge!
Try reversing the polarity on your voltage measurement (just interchange
the 1+ and 1- terminals). This should just change the sign on the
Use channel 2 of the voltmeter (the 2+ and 2- terminals) to
measure the voltage across the resistor. Set your polarity such that the assumed
positive voltage is at the V+ connection, and the assumed negative voltage
is at the diode's anode.
Reverse the polarity on the resistor measurement and verify that the
sign on the measured voltage changes.