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Sinusoids and Swept Signals

Project 2: Waveform Generator

tag Analog Discovery AWG

Sinusoids and Swept Signals

Project 2: Waveform Generator

Introduction

Related Material:
Periodic Signals
Sinusoids
Swept Sines

In this experiment, we will use the Arbitrary Waveform Generator (AWG) on the Analog Discovery™ to apply sinusoidal and swept sinusoidal voltages to a speaker. Sinusoidal signals are a special type of periodic signal which varies according to the mathematics of sine and cosine functions. Human perceptions are often geared toward sinusoidal signals—sinusoidal pressure waves are heard as “tones”, and sinusoidal light waves have a particular “color”.

Sinusoidal sweeps are signals which are composed of sinusoids of varying frequency—in particular, the signals we will use here have frequencies which increase with time. Sinusoidal sweeps are described in slightly more detail in the Swept Sines link associated with this experiment.

Our goal in this experiment is to obtain an intuitive feeling for the properties of sinusoids and swept sinusoids and to understand the more abstract representations of these signals as they were presented in the Sinusoids and Swept Sines links. This experiment also introduces the “Sweep” tab on the Analog Discovery's arbitrary waveform generator instrument.

Before you begin, you should:
  • Be able to use the Analog Discovery Waveform Generator to apply standard periodic voltage signals to a circuit.
  • Sketch a sinusoidal signal. Label the amplitude and period on the sketch.
  • Determine the frequency of a sinusoidal signal from its period.
  • State how the period of a swept signal changes with time.
After you're done, you should:
  • Use the Analog Discovery waveform generator to create swept signals.

Inventory:

Qty Description Typical Image Schematic Symbol Breadboard Image
1 Buzzer/Speaker
The Buzzer/Speaker in the analog parts kit has two terminals. If a time-varying voltage is applied between the terminals a film in the speaker vibrates, converting the voltage waveform to a pressure waveform with a similar “shape”. Note: The speaker in your parts kit may have different markings than the one pictured.

Procedures

Step 1: Understanding the Circuit

A. Circuit Schematic

  1. Connect one terminal of the speaker to the W1 terminal of your Analog Discovery.

  2. Connect the other terminal of the speaker to a ground terminal on your Analog Discovery.

B. Create Circuit

  1. Insert the terminals of the speaker into your breadboard so that they are in different rows.

  2. Connect W1 (the yellow wire) to one terminal of the speaker.

  3. Connect ground (, the black wire) to the other speaker terminal.

Step 2: Set up Instruments

A. Open WaveGen Instrument

  1. Open WaveForms™ to view the main window.

  2. Click on the WaveGen icon to open the waveform generator.

B. Set Up WaveGen to Apply a Sinusoidal Wave to the Speaker

*Make sure symmetry is set to 50%

Step 3: Experiment

A. Apply Power to the Speaker

  1. You should hear a tone from your speaker.

  2. Slowly increase the frequency of the voltage applied to the signal using the slider bar on the frequency control.
    • Does the resulting sound agree with your expectations?
    • Is the volume of the sound constant as the frequency increases?
    • At what frequency can you no longer hear sound from the speaker?

B. Apply a Swept Sine to the Speaker

  • The sound from your speaker should start out at a low frequency (100Hz) and increase to a high frequency (10kHz) over a period of two seconds.

Test Your Knowledge!

  1. Change the lower and upper frequencies and the sweep time. Do these controls have the effect you would expect?

  2. Try changing the amplitude with time. Start with the settings shown below:
    3. The images above are screenshots of Digilent WaveForms running on Microsoft Windows 7.
  3. The sound you hear now should get louder and softer, in addition to changing frequency.
    • Does the sound you hear agree with your expectations?
  4. Try changing both the damping time and the sweep time to get a feeling for their effects.
    • Does turning sweep to “Off” have the effect you would expect?
  • Other product and company names mentioned herein are trademarks or trade names of their respective companies. © 2014 Digilent Inc. All rights reserved.
  • Circuit and breadboard images were created using Fritzing.