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Set up an FFT display

Learn how to monitor data in a Fast Fourier Transform (FFT) by displaying a sensor measurement versus frequency.

In this tutorial, we're going to use a Wireless Sound Sensor (PS-3227) to measure the resonant frequencies produced by plucking a guitar string on the PASCO Sonometer (WA-7428). If you have a PASPORT or Science Workshop sensor, see Connect a sensor to Capstone for more information.

Set up the experiment

Connect the sensor to Capstone and set up the FFT display.

  1. Click New Experiment to create a new Capstone file.

  2. Click the Sensor Data menu and select FFT.

  3. Turn on the sensor by pressing the power button until the lights turn on.

  4. Select the sensor that matches the device ID printed on your sensor.
  5. Click Hardware Setup in the Tools palette to close the Hardware Setup panel.

Collect data

In this step, we're going to monitor the frequencies produced by the guitar string. It is important to recognize that we are monitoring the data instead of recording it. Monitoring is required for high sample rates due to limitations in transferring large amounts of data.

  1. Click Monitor to begin monitoring data.
  2. Pluck a string to produce a sound.
  3. Adjust the axis scales to a useful range. Drag the Frequency axis until the maximum range is around 2,000 Hz. You can also drag the vertical axis or use the normalize data tool to make 1% the maximum value.
  4. Pluck the string again. Since data is not being recorded, click Stop to freeze the data on the display. This might take a few attempts.

Record the run

As mentioned previously, we have been monitoring the data instead of recording the data. If you want to keep a run, you need to click the Snapshot tool. This records a run called FFT Snapshot #1.

You can now monitor additional data without losing your original data. Additionally, you can display multiple runs in the FFT display or display this run in a Graph display for further analysis.

Measure the peak frequencies

Use the coordinates tool to measure the resonant frequencies.

  1. Click one of the peaks to analyze.
  2. Click the Coordinates tool. A box displaying the coordinates appears.
  3. Repeat to display the frequencies of other peaks.

Measure the difference between peaks

  1. Click the coordinates box, then select the Delta tool. A second coordinates box appears.
  2. Drag the second coordinates box to a new location to determine the difference between the two points. Boxes showing the difference in y and the difference x appears.

Next steps

Learn more about the tools provided in the FFT display by visiting the FFT display page.