Rico

2.4  Lab Exercise: Voltage Dividers

Objectives

  1. Understand voltage and signal generation
  2. Understand voltage and signal measurement
  3. Become familiar with the instruments used for voltage and signal generation and measurement
  4. Become familiar with prototyping circuits
  5. Deepen understanding of voltage dividers
  6. Model real circuits
  7. Learn to acquire voltage measurements with the myRIO
  8. Learn to plot and export plots in Python

Materials

  • PC with LabVIEW installed
  • myRIO configured with LabVIEW
  • Multimeter
  • DC power supply
  • Breadboard
  • Jumper wires
  • Resistors:
    • two 1.5 MΩ
    • one each of 2.2 MΩ, 3.3 MΩ, 4.7 MΩ
  • Function generator
  • Oscilloscope
  • Two BNC cables
  • One BNC Y- or T-connector

Building a Voltage Divider Circuit

  1. Measure and record the actual resistance of each resistor:
\(R_1\)\(R_2\)\(R_3\)\(R_4\)\(R_5\)
Nominal (MΩ)1.51.52.23.34.7
Measured (MΩ)
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  1. Connect the two 1.5 MΩ resistors in series.
  2. Connect the DC power supply across the series resistors.
  3. Set the power supply to 10 V (see [@res:supplying-voltage]).

Measuring with a Multimeter

  1. Measure the voltage across each resistor:
\(v_{R_1}\)\(v_{R_2}\)
Measured (V)
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  1. Measure the voltage across both resistors (source voltage):
\(\widetilde{V_s}\)
Measured (V)
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  1. Record the voltage and current from the power supply front panel:
\(V_s\) (V)\(I_s\) (mA)
Readings
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  1. Replace the output resistor \(R_2\) with 2.2 MΩ and repeat.
  2. Repeat for 3.3 MΩ and 4.7 MΩ.

Summary Table

Record \(\widetilde{R_i}\), \(\widetilde{V_s}\), and \(\widetilde{v_{R_i}}\) for each \(R_i\) in the table below:

\(R_2\)\(R_3\)\(R_4\)\(R_5\)
Nominal \(R_i\) (MΩ)1.52.23.34.7
Measured \(\widetilde{R_i}\) (MΩ)
Measured \(\widetilde{V_s}\) (V)
Measured \(\widetilde{v_{R_i}}\) (V)
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myRIO Measurements

  1. Build the original divider with two 1.5 MΩ resistors; do not power it yet.
  2. Connect the myRIO to power and USB.
  3. Use MSP connector C (figure 1).
Figure 1: myRIO Connector C

  1. Connect:

    • AGND (3) to circuit ground
    • AO1 (5) to other end of series resistors
    • AGND (6) and AI0- (8) to ground
    • AI0+ (7) to node between resistors (output node)

  2. Download and extract Lab Stubs to the PC.

  3. Open Lab 02 project and implement:

    • AO0 output controlled from front panel
    • AI0+ measured continuously
    • Both voltages plotted on same chart
    • Digital readouts of current values

    The front panel and block diagram should look something like what are shown in figure 2 and figure 3, respectively.

    Figure 2: Example front panel
    Figure 3: Example block diagram

  4. Sweep \(V_s\) from 0 to 10 V and record measured outputs.

  5. Repeat for each output resistor: 2.2 MΩ, 3.3 MΩ, 4.7 MΩ.

Summary Table

\(R_i\)Quantity012345678910
\(R_2\)\(\widetilde{V_s}\) (V)
\(R_2\)\(\widetilde{v_{R_2}}\) (V)
\(R_3\)\(\widetilde{V_s}\) (V)
\(R_3\)\(\widetilde{v_{R_3}}\) (V)
\(R_4\)\(\widetilde{V_s}\) (V)
\(R_4\)\(\widetilde{v_{R_4}}\) (V)
\(R_5\)\(\widetilde{V_s}\) (V)
\(R_5\)\(\widetilde{v_{R_5}}\) (V)
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Signals from the Function Generator

  1. Set the function generator:
    • Waveform: sine
    • Frequency: 10 kHz
    • Amplitude: 5 Vpp
  2. Connect OUTPUT to oscilloscope CH1. Confirm:
    • AC coupling
    • Vertical mode: CH1 or DUAL
    • Trigger: AUTO and CH1
    • Probe setting: 1X
  3. Adjust oscilloscope for stable waveform.
  4. Record:
\(\widetilde{V_s} = \widetilde{v_{R_2}}\) (Vpp)\(T\) (ms)
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  1. Switch waveform to square, triangle, sawtooth, then back to sine.
  2. Set frequency to 10 Hz.
  3. Adjust TIME/DIV to observe waveform sweep.
  4. Profit.

Report Requirements

Your report should include:

  1. Circuit analysis of each configuration using \(R_1\) and \(R_2\), modeling each source.
  2. Plot of multimeter measurements of input and output voltage vs. resistor value. Use marker-only plots (e.g., ×, ○) and add theoretical predictions as continuous lines.
  3. Plot of myRIO measurements: \(\widetilde{V_s}\) vs. \(\widetilde{v_{R_i}}\) for each \(R_i\), with theoretical predictions.
  4. Table of all multimeter measurements (resistance and voltage).

Photos taken during the lab may be included.