Measuring An Arduino Servo Signal With An AD2 In LabVIEW

Materials Needed

• 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

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.

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. In the previous exercise when we tied AWG1 to OSC1, the signal and the scope have the same ground (the Analog Discovery 2 ground). 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.

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.

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.

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.

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