University of Puerto Rico at Mayagüez
Department of Mechanical Engineering
INME 4235 – MECHANICAL ENGINEERING LAB I
TASK 9: Introduction to Microprocessor-Based Measurements
Objective: The purpose of this task is to familiarize you with the BX-24 Developer’s
Board and review electric circuit theory. With the opportunity to see a full measurement
system, including the sensor, transduction, signal conditioning, and output stages of
measurement.
Reading assignment for this task:

BasicX Quick Tour

Handout on Useful Basic X Commands and Calls

Class 9 or Task 9 Adendum
Materials:
To carry out this task the following are provided in the laboratory:
1. Thermistor.
2. Wheatstone bridge circuit
3. Osciloscopio.
Procedure:
Reading Assingment for this task:
For this task, you will not turn in the usual report. Rather, you will hand in specific results
for each of various activities that will get you started on microprocessor-based
measurements. In Tasks 9 and 10, you will have
1
The task includes four main objectives in support of its purpose:
1. Explain all steps in a simple BasicX program.
2. Display numbers in a 7-segment LED array through BasicX commands.
3. Write a program to measure the time in between two consecutive presses of a
button.
4. Calculate the output of an 8-bit D/A converter for the eight combinations of digital
inputs.
2
Task 9a: BX-24 Developer’s Board and BasicX Commands
You will use a computer to communicate with the BX-24 Developer’s Board. Turn the
computer on and start the BasicX Environment. Power the BX-24 Developer’s Board and
connect the serial cable between the board and the PC. Set working directories and verify
proper communication settings. Open and monitor port COM1.
Compile and run program Task9a.bxp, which we will use to verify port communication
and note the structure and function of various useful BasicX Commands. Please see the
Class 9, section 1, and answer the questions about the program on your task
report.
PART 9A
Sub Main()
Dim
Dim
Dim
Dim
Dim
Dim
Dim
Counter1 As Integer
Counter2 As Integer
Firstnumber As Single
Secondnumber As Single
Answer1 As Single
Answer2 As Single
Answer3 As Single
Firstnumber = 3.0
Secondnumber = 4.0
For Counter1 = 1 To 3
If (Counter1 = 1) Then
Answer1 = Firstnumber + Secondnumber
Debug.Print
Debug.Print "Three plus four is: "; CStr(CInt(Answer1))
ElseIf (Counter1 = 2) Then
Answer2 = Firstnumber * Secondnumber
Debug.Print "Three times four is: "; CStr(CInt(Answer2))
ElseIf (Counter1 = 3) Then
Answer3 = (Firstnumber*100.0)/Secondnumber
Debug.Print "Three divided by four is: "; CStr(CInt(Answer3)); " hundredths"
Debug.Print
End If
Next
Counter2 = 1
Do While Counter2 <=4
Debug.Print "Mechanical Engineers know electronics."
Counter2 = Counter2+1
Call Delay(3.0)
Loop
End Sub
3
Task 9b: Numeric Displays
For this second experiment, you will have BasicX count the numbers 0 to 9 and show the
numbers in a seven-segment LED display. Please see the Task 8-Addendum, section 2.
Create a program containing individual subprocedures for each number.
Make the
appropriate connections from the BX-24 system to the PC and from the BX-24 system to
the breadboard. Using a Do-Loop command, have the program count from 0-9 and start
over indefinitely. To be able to see the numbers, put in a Delay command in between
number subprocedure calls. Show your results to your instructor and copy the program
on a floppy disk. Then, hand your program in with your report.
first
Sub Main()
Debug.Print "comienzo "
Dim Switch As Byte
Do
Switch = GetPin(11)
Debug.Print "el estado del boton es"; CStr(CInt(Switch))
If (Switch = 1) Then
Call Nine
Call Borrar
Call Eight
Call Borrar
Call Seven
Call Borrar
Call Six
Call Borrar
Call Five
Call Borrar
Call Four
Call Borrar
Call Three
Call Borrar
Call Two
Call Borrar
Call One
Call Borrar
Call Cero
Call Borrar
Delay(5.0)
End If
Loop
End Sub
Sub One()
Call PutPin(20,0)
Call PutPin(18,0)
Delay(0.5)
4
Call Borrar()
Delay(0.5)
End Sub
Sub Two()
Call PutPin(5,0)
Call PutPin(20,0)
Call PutPin(19,0)
Call PutPin(7,0)
Call PutPin(16,0)
Delay(0.5)
Call Borrar()
Delay(0.5)
End Sub
Sub Three()
Call PutPin(5,0)
Call PutPin(20,0)
Call PutPin(19,0)
Call PutPin(18,0)
Call PutPin(16,0)
Delay(0.5)
Call Borrar()
Delay(0.5)
End Sub
Sub Four()
Call PutPin(6,0)
Call PutPin(19,0)
Call PutPin(20,0)
Call PutPin(18,0)
Delay(0.5)
Call Borrar()
Delay(0.5)
End Sub
Sub Five()
Call PutPin(5,0)
Call PutPin(6,0)
Call PutPin(19,0)
Call PutPin(18,0)
Call PutPin(16,0)
Delay(0.5)
Call Borrar()
Delay(0.5)
End Sub
Sub Six()
Call PutPin(5,0)
Call PutPin(6,0)
Call PutPin(7,0)
Call PutPin(16,0)
Call PutPin(18,0)
Call PutPin(19,0)
Delay(0.5)
Call Borrar()
Delay(0.5)
End Sub
Sub Seven()
Call PutPin(5,0)
Call PutPin(20,0)
Call PutPin(18,0)
Delay(0.5)
Call Borrar()
5
Delay(0.5)
End Sub
Sub Eight()
Call PutPin(5,0)
Call PutPin(6,0)
Call PutPin(7,0)
Call PutPin(19,0)
Call PutPin(18,0)
Call PutPin(16,0)
Call PutPin(20,0)
Delay(0.5)
Call Borrar()
Delay(0.5)
End Sub
Sub Nine()
Call PutPin(5,0)
Call PutPin(6,0)
Call PutPin(19,0)
Call PutPin(18,0)
Call PutPin(16,0)
Call PutPin(20,0)
Delay(0.5)
Call Borrar()
Delay(0.5)
End Sub
Sub Cero()
Call PutPin(5,0)
Call PutPin(6,0)
Call PutPin(7,0)
Call PutPin(18,0)
Call PutPin(16,0)
Call PutPin(20,0)
Delay(0.5)
Call Borrar()
Delay(0.5)
End Sub
Sub Borrar()
Call PutPin(5,1)
Call PutPin(6,1)
Call PutPin(7,1)
Call PutPin(19,1)
Call PutPin(18,1)
Call PutPin(16,1)
Call PutPin(20,1)
End Sub
a pin 5
b pin 20
c 18
d 16
e pin 7
f pin 6
g 19
6
Task 9c: Buttons and Timing
Task 9c asks you to count the time elapsed in between two consecutive pushes of a
button. Since the pushbuttons on the BasicX program require debouncing, the smallest
time difference that you will detect is 0.1 seconds. However, for any two consecutive
presses of a button greater than 0.1 seconds apart, you will be able to measure the time
elapsed in between presses with a fair amount of accuracy (in the order of milliseconds).
Connect the output of an on-board pushbutton to pin 12 of the BX-24 board. Then, run
the program Task9c.bxp, which will read the state of the pin. When the button is pressed,
the program requests the time on the BasicX real time clock. When the button is pressed
a second time, the program requests the time again. It then uses a variable to calculate
the difference in between these two times. Note that, to get millisecond accuracy, the
program separates the integer part from the decimal part. It then multiplies the decimal
part by 1000 and reports both the seconds and milliseconds to the screen.
Explain how this program works, by stating in your own words what each
statement does inside the larger Do-Loop, starting with the Do command and
ending with the Loop command.
Sub Main()
Dim
Dim
Dim
Dim
Dim
Dim
Dim
Dim
T1 As Single
T2 As Single
DT As Single
DT_Int As Single
DT_Decimal As Single
DT_Dec_in_ms As Single
PinState As Byte
Cycle As Boolean
Debug.Print "Starting"
PinState = 0
Do
PinState = GetPin(11)
Delay(0.2)
If (PinState = 1) Then
T1 = Timer
PinState = 0
Cycle = True
7
Do While Cycle = True
PinState = GetPin(11)
Delay(0.2)
If (PinState = 1) Then
T2 = Timer
DT = T2-T1
DT_Int = Fix(DT)
DT_Decimal = DT-DT_Int
DT_Dec_in_ms = DT_Decimal*1000.0
Debug.Print "The time elapsed is "; CStr(CInt(DT_Int));" seconds"
Debug.Print "and "; CStr(CInt(DT_Dec_in_ms)); " milliseconds"
call freqout(4,1010,0,1.0)
PinState = 0
Cycle = False
End If
Loop
End If
Loop
End Sub
8
Task 9d: Determining Digital-to-Analog Converter Output
An eight-bit D/A Converter is shown in the Class 9, section d.
This eight-bit converter is made up of 3 voltage sources and seven resistances arranged
in a network. The voltage sources will be output pins of the BX-24 system, which we can
set to 0 or 5 Volts. (Zero volts means disconnecting the source, 5 Volts means supplying
5 Volts to the network at the location of the source.) Two of the resistances have the
same value R and five of the resistances have values 2R. The output voltage is
measured across one of the 2R resistances toward the right side of the network, as
indicated in the figure. If you recall that voltage potentials increase across a voltage
source (from – to + leads) and voltage potentials drop across resistances, then you may
already suspect that the output voltage will be different at the output node if sources
and/or resistors are removed from the circuit. This is exactly what occurs when we turn
off any of the three BX-24 output pins (that, in turn, are sources on the D/A converter’s
circuit).
Task 8d is for you to analyze the eight circuits that result when the three BX-24 output
pins used as sources on the D/A converter are either turned on or off. Fill in a table like
the one in the Class 9, part d, and hand it in as part of your report.
Pin 1
Pin 2
Pin 3
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
9
Vout
HOMEWORK 1:
Write a BasicX program program that writes “HELLO[#group number][student #]”.
HOMEWORK 2:
Read the following BasicX program. Then, describe what the program does. Include the
control structures, the calculations, and subprogram calls in your explanation. Do not
generalize, be specific to this program! You will receive credit on the understanding that
you demonstrate. The student who wrote the program made a mistake. What is it?
Sub Main()
Dim
Dim
Dim
Dim
Dim
Dim
N As Single
Dl As Single
Aux2 As Single
Auxl As Single
D As Integer
I As Integer
Debug.Print
N=48357.4
Debug.Print
I = 1
Do While I <= 6
If (I <> 1) Then
Auxl = N/10.0
Aux2 = Fix(Auxl)
Dl = (Auxl-Aux2)*10.0
ElseIf (I = 1) Then
Aux2 = Fix(N)
Dl =(N-Aux2)*10.0
End If
D = CInt(Dl)
Debug.Print CStr(D)
If (D = 1) Then
Debug.Print
Call Delay(l.O)
Call One()
ElseIf (D = 2) Then
Debug.Print
Call Delay(2.0)
Call Two()
ElseIf (D = 3) Then
Debug.Print
Call Delay(1.0)
Call Three()
ElseIf (D = 4) then
Debug.Print
Call Delay(2.0)
Call Four()
ElseIf (D = 5) Then
Debug.Print
Call Delay(1.0)
10
Call Five()
ElseIf (D = 6) Then
Debug.Print
Call Delay(2.0)
Call Six()
ElseIf (D = 7) Then
Debug.Print
Call Delay(1.0)
Call Seven()
ElseIf (D = 8) Then
Debug.Print
Call Delay(2.0)
Call Eight()
ElseIf (D = 9) Then
Debug.Print
Call Delay(1.0)
Call Nine()
ElseIf (D = 0) Then
Debug.Print
Call Zero()
End If
N=Aux2
I=I+1
Loop
End Sub
Sub One()
Call PutPin(5,0)
Call PutPin(6,0)
Call PutPin(7,0)
Call PutPin(8,0)
Call PutPin{15,0)
Call PutPin(16,0)
Call PutPin(17,l)
End Sub
Sub Two()
Call PutPin(5,0)
Call PutPin(6,l)
Call PutPin(7,l)
Call PutPin(8,l)
Call PutPin(15,0)
Call PutPin(16,1)
Call PutPin(17,0)
End Sub
Sub Three( )
Call PutPin(5,0)
Call PutPin{6,0)
Call PutPin(7,0)
Call PutPin(8,0)
Call PutPin(15,0)
Call PutPin(16,0)
Call PutPin(17,0)
End Sub
Sub Four()
Call PutPin(5,0)
Call PutPin(6,0)
Call PutPin(7,l)
Call PutPin(8,0)
Call PutPin(15,0)
Call PutPin(16,0)
Call PutPin(17,l)
End Sub
11
Sub Five()
Call PutPin(5,l)
Call PutPin(6,0)
Call PutPin(7,l)
Call PutPin(8,l)
Call PutPin(15,0)
Call PutPin{16,0)
Call PutPin(17,0)
End Sub
Sub Six()
Call PutPin(5,0)
Call PutPin(6,l)
Call PutPin(7,l)
Call PutPin(8,0)
Call PutPin(15,0)
Call PutPin(16,0)
Call PutPin(17,0)
End Sub
Sub Seven()
Call PutPin(5,0)
Call PutPin(6,l)
Call PutPin(7,0)
Call PutPin(8,0)
Call PutPin(15,l)
Call PutPin(16,0)
Call PutPin(17,0)
End Sub
Sub Eight()
Call PutPin(5,l)
Call PutPin(6,l)
Call PutPin(7,l)
Call PutPin(8,l)
Call PutPin(15,0)
Call PutPin(16,1)
Call PutPin(17,0)
End Sub
Sub Nine()
Call PutPin(5,0)
Call PutPin(6,0)
Call PutPin (7,0)
Call PutPin(8,0)
Call PutPin (15,0)
Call PutPin(16,1)
Call PutPin(17,0)
End Sub
Sub Zero()
Call PutPin(5,0)
Call PutPin(6,0)
Call PutPin(7,l)
Call PutPin(8,0)
Call PutPin(15,0)
Call PutPin(16, 0)
Call PutPin(17,0)
End Sub
12
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