2. Measuring An Arduino Servo Signal With An AD2 In LabVIEW

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Things Used In This Project

Hardware components:

  1. Digilent Analog Discovery 2
  2. Servo (generic)

Software apps and online services:

  1. Digilent LabVIEW Home Bundle

Materials Needed

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  • Everything from Setup (OpenScope, micro USB, wires)
  • Breadboard (from Parts Kit)
  • Servo (from Parts Kit)
  • Arduino
  • USB-B Cable
  • Mini Grabbers
  • Analog Discovery 2
  • LabVIEW

Verifying Your Servo Signal
Connect your Servo to your Arduino using breadboard wires.

  • Orange servo wire – Pin 9
  • Red servo wire – Power 5V
  • Black/Brown servo wire – GND
  • The servo should be in SWEEP mode

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PWM

  • The Arduino implements a PWM signal, that is a square wave with a duty cycle that can range from 0% to 100%.
  • We will use LabForms and the Analog Discovery 2, to see exactly how long the duty cycle is on, what voltage, and duration.

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Connect the Analog Discovery 2 to the Arduino

  • Disconnect the Servo
  • Remember, the PWM Signal for the Servo is on Pin 9 of the Arduino.
  • Use a breadboard wire, connect OSC1 (Orange Wire) to Pin 9.
  • Close out LabForms, open up a new window (so the settings reset to default).
  • Hit Run.

Grounding the Oscilloscope Channel

  • Anytime you use your Oscilloscope channel, you need to have a Ground connected.
    Since the Arduino is on a different circuit, the Analog Discovery 2 needs to know its ground in order to correctly measure the signal. Let’s demonstrate this.

  • Plug a breadboard wire into the Analog Discovery 2 analog ground (orange or blue with white stripe) and plug it into one of the Arduino Ground Pins.

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Adjust the signal on the screen

  • The Arduino puts out 5V signals. We suggest “zooming out” so you have the signal cleanly on your screen.

  • “Volts/” will allow you to change the Y Scale of the graph. Offset will allow you to move where 0 is.

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Best Fit

  • It’s important to make sure that the screen is “focused” on the part of the waveform with the information we need.

  • For this exercise we are interested in what happens when the signal goes high, so the top of the waveform needs to be seen.

  • Change your Volts/ Division to 1.00 V and Offset to 1.5 V (you can scroll or type it in). You can also type in mV instead of V.

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Cursor

  • Cursors are a way in which you can set points of interest on a screen, and display the exact value.
  • LabForms allows you to put single cursors on Time or Voltage.
  • Time – We’ll use this to see if the PWM signal has a consistent duty cycle
  • Voltage – We’ll use this to see what Voltage the PWM signal peaks at.

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Test our cursors

  • Hit SINGLE to capture a single acquisition of the waveform
  • Turn on Cursors, select Time
  • Line the cursors up with the edges of the signal by moving the dotted lines at the top of the graph
  • Pay attention to the calculations to the right of the cursors button
  • Follow the same procedure for Voltage

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CODE

Labforms.viGoDownload
LabVIEW code