MEM 639 Real World Microcomputer Control 1
Hands-on Lab
LabVIEW – NI-DAQ Analog Input and Output
The USB-6211 provides eight differential 16-bit analog input channels and two 16-bit analog
output channels. These serve to introduce data acquisition and signal generation concepts.
Concept 1: Use an analog output VI to create a virtual variable DC power supply.
Step 1: Create the front panel and block diagram
From the Numeric Controls category, drag Knob and Meter controls into an empty VI front
panel (see Figure 1-1A). Change their range to read -10 to +10 as follows. Right click over the
knob and choose Properties – Scale and change the Minimum and Maximum ranges. Do
the same for the meter. The block diagram, shown in Figure 1-1B uses a While loop.
Figure 1-1B: Corresponding Block Diagram
Figure 1-1A: DC Power Supply Front Panel
Step 2: Configure DAQ Assistant for Analog Output
Launch DAQ Assist. Choose Generate Signal, Voltage and ao0 (analog output
channel 0) as shown in Figures 1-2A and 1-2B.
Figure 1-2A: Select Analog Output - Voltage
Figure 1-2B: Select analog output channel 0
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MEM 639 Real World Microcomputer Control 1
Configure the next pop up box to look like Figure 1-2C. The Signal Output Range has Max
and Min values of 10 and -10 respectively. Also, set the Generation Mode to “1 Sample (On
Demand)”.
Figure 1-2C: Generation Mode set for 1 Sample (On Demand)
Step 3: Attach a voltmeter and test program.
Save program as usb6211AnalogOutput1_0.vi. Attach a voltmeter’s anode (positive lead) to
the DAQ Pin 12 (AO0) and cathode (negative lead) to the DAQ Pin 11 (DGND).
From the front panel, click the Play button (white arrow). Drag the knob to set various voltages.
Observe that the panel’s meter reading corresponds to the same value displayed by the
voltmeter.
Exercise 1: In LabVIEW create programs for the following:
1.1. Create a sine wave function generator. Use two knobs to set the frequency in Hz and
amplitude (0 to 10 Volts). Use a Waveform Graph control to display the sine wave. Hint: for
the block diagram, employ the Sine Wfm element (click Signal Processing – Wfm
Generation). Save file as usb6211FunctionGenerator1_0.vi.
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MEM 639 Real World Microcomputer Control 1
Concept 2: Employ an analog input channel to read a voltage divider circuit
A potentiometer is a variable resistor.
Audio systems often use pots for
volume knobs. Reading the voltage
drop across the pot’s wiper enables
one to calculate resistance and thus
determine the pot’s knob position.
Such a setup is often used to build
rotary and linear encoder circuits. The
photo below shows that a pot is a 3legged device and can be used for a
voltage divider. Recall that
VB =
RB
VA
RA + RB
B
Photo: A pot to sense knob position
Step 1: Create a front panel and block diagram
Figure 2-1A shows that two Numeric Indicators are used in the front panel to display the
measured voltage VB and the calculated resistance RB . Note, these indicators are represented
by DBL (doubles). The block diagram in Figure 2-1B is wired up accordingly.
Figure 2-1A: Two numeric indicators
Figure 2-1B: Block diagram displays voltage
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MEM 639 Real World Microcomputer Control 1
Step 2: Set up DAQ Assistant
Figure 2-2B: Select ai0
Figure 2-2A: Select Analog Input
Make sure the Acquisition Mode is set to “N Samples” as shown in Figure 2-2C. Also set
the Sample Input Range to -10 to 10. Save file as usb6211VoltageDividor1_0.vi
Figure 2-2C: Select “N Samples”
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MEM 639 Real World Microcomputer Control 1
Step 3: Breadboard the voltage divider
Measure the pot’s total resistance by connecting an ohmmeter to the left and right leads (see
Figure 2-3A). Use this value in the block diagram to represent RA + RB .
Figure 2-3A: Pot max value (left and right leads)
To measure resistance RA , connect one of the ohmmeter’s leads to the wiper. Verify that rotating
the pot’s knob changes RA . Also measure RB and verify that RA + RB always equals the pot’s
total resistance value.
Step 4: Acquire the voltage divider reading and display.
Figure 2-4A: Voltage drop measured on analog channel 0
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MEM 639 Real World Microcomputer Control 1
Refer to Figure 2-4A for the hookup. Attach the DAQ Pins 15 (+AI0) and 16 (-AI0) to the pot’s
wiper and rightmost lead (furthest from the pot’s knob) to measure the voltage drop VB . Connect
the DAQ Pin 10 (+5V) to the pot’s leftmost lead (closest to the pot’s knob). Connect the DAQ Pin
11 (DGND) to the pot’s rightmost lead. Execute the program by clicking the Continuous Play
button on the front panel.
Verify that changing the pot’s value changes the measured voltage and updates the calculated
resistance value.
Exercise 2:
2-1. Modify usb6211VoltageDivider1_0.vi to also measure the voltage drop VAB across
resistor RA . Do this with analog input channel 1 (AI1). Display both acquired voltages
( VAB and VB ) and the calculated resistances ( RA , RB , RA + RB ).
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