# lab2

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EGR 345-03

Laboratory Exercise #2

Title: Computer Based Data Collection

Author: Joel Geerlings

Date: September 13, 2001

Purpose:
Use computers with LabVIEW to collect data.

Theory:
To obtain the greatest power and flexibility, engineers must often write their own
computer programs. Traditional programming languages are often awkward to
use when designing user interfaces and dealing with data flows. LabVIEW
avoids this by allowing the user to design systems graphically by connecting
graphical symbols with “wires” (lines).

Computers read data at discrete points in time, much like a strobe light, and then
use the data for calculations. LabVIEW is useful for data collection. Programs
can be written by drawing function blocks and connecting them in the order the
data must flow. This lab exercise involves using LabVIEW to connect to a data
acquisition (DAQ) board. The DAQ allows data from the outside world to be
collected, and changes the outside world through outputs.

When a computer connects to the outside world using an interface card, specific
inputs and outputs must be addressed. The first portion of the address is the board
number of the DAQ, which is „1‟ in this case. The DAQ contains many inputs
and outputs. For analog outputs, the DAQ contains two channels, 0 or 1. For
analog inputs, there are 8 channels, numbered 0 to 7. For digital I/O, there are 24
pins, spread across 3 ports; therefore, when collecting inputs and outputs, we must
specify which port (PA=0, PB=1, PC=2) and which channel from 0 to 7. Digital
I/O ports can be used for input or output, but each port can only serve one
function.

The voltage levels of inputs and outputs are also important. Digital outputs are
only 0V or 5V. Analog inputs and outputs vary from –5V to 5V. If these values
are exceeded significantly, the board can be permanently damaged.

Equipment:
PC with LabVIEW software and PCI-1200 DAQ Card
Interface cable
Digital Multimeter

Procedure and Discussion:
The LabVIEW Quickstart guide was reviewed and the prelab exercise was
performed. The prelab exercise involved writing a LabVIEW program capable of
counting from 1 to 100, squaring the values, and printing the results in a strip
chart. This was performed by setting up a FOR Loop designed to repeat 100
times. Each time the loop was executed, „i‟ was incremented by 1, the value was
squared, and it was printed in the strip chart. The prelab exercise proved to be
difficult because it was an unfamiliar program, and understanding how to properly
set up a loop took a few attempts.

The first exercise in the lab involved writing a LabVIEW program capable of
inputting a signal from a signal generator and graphing it. The function generator
on the CADET trainer was used to produce a 5V waveform with a frequency of
which was pin 1 on the interface cable. The ground on the trainer was connected
to AIGND (analog ground), which was pin 0 on the cable. The „DAG Configure‟
software was then used to verify the hardware was properly setup. Once the
hardware was working properly, the LabVIEW program was written/designed.
The LabVIEW program involved inputting the signal and the ground with a single
analog input, and sending the signal to a waveform chart. The program operated
correctly and enabled the computer to collect data from the outside world (the
function generator) and display it in a chart.

The second exercise involved setting up a voltage output that could be controlled
by the user. A voltage input knob and an output meter were used in the
LabVIEW program to supply a voltage and monitor it. This function was tested
and the input knob worked with the output meter showing the voltage. Then the
program was expanded to output the voltage to a digital multimeter on
DAC0OUT (digital to analog converter output 0) or pin 10. A DMM, grounded
on AGND (analog ground), or pin 11, measured the voltage output. This was
measured to verify the knob and meter. The DMM showed that the program
worked correctly, and that the computer could be used to output a user-controlled
voltage.

The third exercise involved inputting a signal from a manual switch to control a
computer simulated LED, while simultaneously outputting a signal from a
computer simulated switch to control a LED on the circuit trainer. First the
circuit trainer was wired to the interface cable. PB0 (digital I/O B-0) or pin 22 on
the cable was connected to an LED on the trainer. PA0 (digital I/O A-0) or pin 14
was connected to a logic switch on the trainer. DGND (digital ground) or pin13
was connected to the ground on the trainer. The „DAQ Configure‟ utility was
used to verify the hardware setup, which indicated that PA0 was not inputting
correctly, so PA2 was used instead. With the input working properly, the output
port PB appeared to be malfunctioning, so PC0 was used instead for the output.
Once the hardware problems were taken care of, a program in LabVIEW could be
written to interface with the hardware. To allow a „switch‟ in LabVIEW to
control the LED on the trainer, a “Write to Digital Line” function was used. This
was setup to read the switch on LabVIEW and send a voltage out PA2 if the
switch was on. Next, the LED in LabVIEW had to be programmed to light up
when a voltage was inputted in PC0. A “Read from Digital Line” function was
setup to signal the simulated LED to light up when a voltage came in PC0. This
program worked correctly and showed that a computer can simultaneously control
an outside system, while being controlled by a second outside system.

Results and Conclusions:
In conclusion, the lab exercises all performed correctly. However, some of the
exercises took significant effort getting the hardware and LabVIEW program to
work together properly. The final versions demonstrated the computer‟s
capability to collect data and simultaneously control outside systems.

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