Measure RC Circuit with an OpenScope MZ and LabVIEW

Materials Needed

All included in LabVIEW Interaction Parts Kit

• Two 1K ohm resistors

• Take them from the small bag on your desk

• One 33 μF capacitor

• Take it from the small bag on your desk

• One small breadboard

• Wires

Setup

• Place the 33 μF capacitor on a breadboard, connect the solid orange (OSC1) wire from the OpenScope to the anode (the longer leg) of the capacitor.

• Next, run a 1K resistor from the cathode (the shorter leg) and a wire from the anode to a pin connected to the solid black wire (GND) of the OpenScope.

• Finally run another 1K resistor from the cathode to a pin connected to the solid yellow wire (AWG) of the OpenScope.

Software Settings

These settings are all preset in the LabVIEW VI:

Time

• 50ms/div

Trigger

• Rising edge

• Osc Ch 1

• 100mV

Osc Ch 1

• Volts 200mV

• Offset 400mV

Wavegen

• Square wave

• Frequency 3 Hz

• Amplitude 2 Vpp

• DC Offset 1V

Expected Results RC Waveform

Useful wave shapes can be obtained by using RC circuits with the required time constant. The voltage drop across the capacitor alternates between charging up to Vc and discharging down to zero according to the input voltage. If we apply a continuous square wave voltage waveform to the RC circuit whose pulse width matches that exactly of the time constant of the circuit, then the voltage waveform across the capacitor would look something like this:

Results

If you set up the circuit correctly you should get an output similar to the one seen above. This is in line with our expectations based on the software settings I set in LabVIEW. For more theory and equations, go to Real Analog Chapter 7.

OpenScope MZ is OpenSource!

Hardware​

• Schematic

• Mechanical files

Firmware​

• Arduino IDE and MPLAB X

Waveformslive (WFL)​

• Browser-based UI (local and remote internet)​

• Native iOS and Android Apps​ On GitHub

Digilent Agent (DA)​

• USB/serial communication, setup, local/remote internet connectivity