Using the Voltmeter
Voltmeters are an efficient way to get a direct measurement of the voltage across a component. They are commonly found on digital multimeters (DMMs) but are also available as a tool in the WaveForms software.
- A computer with USB port to run the software
- A potentiometer
- A LED
- A small breadboard
Step 1: Setting up the Software
If you have not already done so, install the WaveForms software by following our Getting Started Guide.
The tool itself is not complex so only a few settings are available by clicking on the gear button next to the
Run button. The update rate can be changed as well as the offset and attenuation of each channel, but the most useful setting is the range setting. By default, the voltmeter tool uses the maximum voltage range of the Analog Discovery 2 – 50 V peak to peak with a resolution of approximately 3 mV. Voltage measurements at this range are imprecise and cannot provide high resolution measurements. More precise measurements can be taken by changing the Range to 5 V.
The Voltmeter tool takes over the oscilloscope channels while running, so simultaneous measurements that also use those channels including the Spectrum Analyzer and Impedance Analyzer will be shown as Busy.
Go back to the Welcome tab of the WaveForms software and click on the icon to open the Power Supplies tab. The positive power supply can be enabled and set here with the negative power supply disabled for this tutorial. More information on how to use the power supplies can be found by following the Power Supplies Tutorial here.
Step 2: Setting up the Circuit
The circuit in this tutorial uses a potentiometer to control the amount of resistance presented to an LED. The Voltmeter tool will be used to measure the voltage across the potentiometer as well as the voltage across the LED. Connect the Scope 1+ channel (solid orange wire) to the positive input of the potentiometer and connect the Scope 1- channel (orange wire with a white stripe) to the output of the potentiometer.
To measure the voltage across the LED, attach the Scope 2+ channel (solid blue wire) to the anode of the LED and connect the Scope 2- channel (blue wire with a white stripe) to the cathode of the LED. Connect the cathode of the LED to a Ground (black wire) provided by the Analog Discovery tool. The negative input of the potentiometer should also be attached to the same ground from the Analog Discovery tool; the positive input on the potentiometer should be attached to the voltage supply input (red wire) from the Analog Discovery tool.
Step 3: Measuring the Voltage
Enable the Master controls on the power supplies to provide energy to the system and click the green Run button on the voltmeter tool. The measured voltage data for each sample including the DC, True RMS, and AC RMS are visible for both channels. Note that the red LED does not light up until there is at least 1.5 V (at least for this particular LED) across the LED.
If you have any further questions about the Voltmeter tool, please ask them on the Scopes and Instruments section of the Digilent technical Forum, https://forum.digilentinc.com/forum/8-scopes-instruments/, where one of the Digilent engineers will be able to see and respond to your question.