• Using the WaveForms Power Supplies and Data Logger with a simple resistor circuit.

This is a quick and simple project that will introduce how to use the WaveForms Power Supplies and Data Logger with the Electronics Explorer Board. The circuit that will be implemented will be a simple network of 4 resistors of varying values. The WaveForms Power Supplies will be used to power the circuit. Two “nodes” of the resistor network will be connected to different voltmeter channels on the EE Board and the WaveForms data logger will be used to measure the voltage at these nodes of interest. As part of this project, a brief background of voltage dividers and series/parallel resistors will be discussed.

• Electronics Explorer Board w/ Power Supply and USB cable
• From the Starter Parts Kit:
  • 470Ω Resistor x 2
  • 1kΩ Resistor
  • 100Ω Resistor
  • Jumper wires
• WaveForms Software ( download) - WaveForms 3.5.4 is used in this tutorial

1. Connect the EE Board to your PC with the USB cable.
2. Connect the board's external power supply and flip the Ready switch to the ON position.
3. Build the circuit.
   • The figure below shows the completed circuit.
4. Launch the WaveForms Software. The Device Manager will pop up. Click your EExplorer on the list and click Select. The WaveForms main window will now appear.
5. Click on the Power Supplies icon to open the Power Supplies for the EE Board. Configure the window that appears as follows:
   • In the top left, deselect all of the boxes except the one corresponding to VP+.
     • VP-, Vcc, Vref1, and Vref2 should be OFF. VP+ should be Rdy.
   • In the box labeled as Positive Supply - VP+ Rdy, set the voltage to 5V and the current to 100mA.
   • In the plot area below that, deselect all the boxes except the Vmtr 1 and Vmtr 2 rows that are measuring a voltage value. These plots are not the ones that will be used in this tutorial, but offer an alternate view. BY clicking on the green plus sign users may add additional plots to the graph including the voltage of the VP+ rail and other mathematically derived plots.
   • Notice that VP+ is the only power supply we have turned on because this is where the power to the circuit is coming from on the EE Board.
   • Confirm your settings are correct by comparing your window to the figure below.
6. Go back to the main WaveForms screen via the Welcome tab and click on the Data Logger icon
   • In the plot area deselect all of the boxes except for the C1 DC and C2 DC (Channel 1 DC and Channel 2 DC inputs).
     • It is recommended that the settings for each of the plots are changed so that they do not auto-range, providing a more clear and less jumpy representation of the voltage divider circuit.
7. After configuring the settings, click the Run button in the Data Logger and on the Power Supplies tab click top left button that says Master Enable. This will turn the power on. Switch back to the Logger window.
8. Observe the results, particularly the values at channels 1 and 2 of the voltmeter on the Logger. The values read by channels 1 and 2 should be around 2.18V and 1.80V, respectively. Note: WaveForms also has a dedicated Voltmeter tool available in addition to the Data Logger. The reason that the Voltmeter is not used in this tutorial is because the voltmeter tool uses the Oscilloscope inputs at the maximum range of 40 V pk2pk, resulting in a resolution of about 40 mV. A brief discussion of voltage dividers and series/parallel resistors will explain how these values can be verified.

The figure to the right shows the original circuit from step 3. Nodes A and B are the locations of the circuit that were measured with channels 1 and 2, respectively. The discussion regarding how the values at nodes A and B were obtained will begin with a discussion of series resistors.

Resistors being in series refers to them being in the same line. To combine resistors in series, simply add their values together. For example: R₃ + R₄ = 100Ω + 470Ω = 570Ω

Applying the principle above, resistors R₃ and R₄ can be combined to a single resistor. This results in a simplified equivalent circuit, shown at the right.

The new simplified circuit consists of two resistors in parallel. When combining resistances in parallel, apply the following formula:

In our circuit, resistors R₂ and R_3,4 are in parallel. Applying the equation above leads to:
This leads to the further simplified circuit shown on the right. This circuit is a simple voltage divider that has isolated node A so the voltage at this node can be easily calculated.

Applying the standard voltage divider equation gives the voltage at node A.

Notice this value matches the voltage measured at channel 1 of the voltmeter!

To find the voltage at node B, we will apply a fundamental concept of parallel circuits. This concept is as follows: Components in parallel, regardless of number or value, have the same voltage drop across them. In our circuit this means that R₂ has the 2.178V from Node A across it. Additionally, resistors R₃ and R₄, when combined, have the same 2.178V across them. We can now apply the same voltage divider equation to R₃ and R₄ to find the voltage at Node B. You may want to refer back to the original circuit (shown again on the right) to see how we applied the voltage divider.

Notice that this matches the voltage measured at channel 2 of the voltmeter!

That concludes this project! Try applying different voltages with VP+ or using different resistor values and check if your measured values match your calculations!