Industrial Control (Students guide, 1999, v1.1 )

Experiment #1: Flowcharting and StampPlot Lite

Figure 1.8: Exercise 3 - Simple Heater Flowchart

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Experiment #1: Flowcharting and StampPlot Lite

Enter and run Program 1.2. Monitor the value in debug window while adjusting the potentiometer and note what occurs as the value rises above 120 and below 100.

Programming Challenge

Modify the process flowchart and program so the LED indicates an air conditioner cycling between 70 and 75 degrees.

Exercise #4: Using StampPlot Lite

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Experiment #1: Flowcharting and StampPlot Lite

While the debug window for the BASIC Stamp is very useful for obtaining data and information from the BASIC Stamp, it can be difficult to visualize the data without careful scrutiny. Is the temperature increasing or decreasing? How quickly is it changing? At what point did the output change? What temperature is it cycling around?

Enter StampPlot Lite! StampPlot Lite (SPL) was specifically developed for this text. SPL accepts data from the BS2 in the same fashion the debug window does, only SPL interprets the data and performs on of 4 actions based on the structure of the data:

•A value is plotted on an analog scale in real time.

•A binary value starting with % is plotted as digital traces in real time.

•Strings beginning with ! are interpreted as instructions to control and configure SPL.

•Any other string is listed as a message at the bottom of SPL and optionally time-stamped.

A main rule of SPL is that each line must end in a carriage return (13 or CR).

Please review Appendix A for a more in-depth discussion of StampPlot Lite.

If you have not yet installed StampPlot Lite, install it on your computer by downloading it from http://www.stampsinclass.com. Double-click the setup button and install it in your designated directory.

Let's take another look at Program 1.2, our simple heater, but this time using StampPlot Lite to help visualize the process. Program 1.2 has been rewritten as Program 1.3 to utilize StampPlot Lite (bold lines are added/modified from program 1.2).

'Program 1.3; Simple Heater using StampPlot Lite

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Experiment #1: Flowcharting and StampPlot Lite

•Enter and run Program 1.3 on your BASIC Stamp.

•Close the BASIC Stamp editor’s blue debug window.

•Select the correct COM port in StampPlot Lite and click 'Connect.'

•

•Reset the BASIC Stamp by pushing the button on the Board of Education. Now you’re ready to use this unique software utility.

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Experiment #1: Flowcharting and StampPlot Lite

At this point you should see data being plotted. Adjust the 10K-ohm potentiometer with your fingers or a small screwdriver. The analog line displays the value of the potentiometer. The digital trace at the top displays the status of the LED indicator. Figure 1.9 is a sample capture of the plot from our circuit.

Figure 1.9: StampPlot Lite Graph of Exercise #4

Note the correlation between the analog value and the switching of the digital output. Use the various controls on StampPlot Lite to become familiar with the functions and features. Analyze Program 1.3 and note the various configuration settings and data sent to the application. Refer to Appendix A for additional information on StampPlot Lite if you are having problems understanding the basics of the software utility.

Programming Challenge

Modify your air conditioner challenge from Exercise #2 to use StampPlot Lite. Configure your program to transmit data approximately every 0.5 seconds. Calculate the number of data points needed to fill the screen within a maximum of 60 seconds, and test.

Just for fun!

Enter and run the following program. The potentiometer simulates a single-handle shower (mixer) valve with adjustment delay. Adjust the shower temperature for a constant 110 degrees. See how fast you can stabilize the temperature at the set point! Press the reset button on the Board of Education and try again. We'll leave it up to you to figure out the program.

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Experiment #1: Flowcharting and StampPlot Lite

'PROGRAM 1.4: ADJUST THE SHOWER!

SetPoint = 110

PAUSE 500

DEBUG "!RSET",CR,"!SPAN 0,200",CR,"!TMAX 30",CR,"!PLOT ON",CR DEBUG "!TSMP ON",CR,"!MAXS",CR,"!PNTS 100",13

DEBUG "!USRS ADJUST THE TEMP FOR ",DEC SetPoint,CR

Main:

HIGH RC

PAUSE 10

RCTIME RC,1,TempSet

TempSet = TempSet/ 30

IF TempSet > CurTemp THEN Higher

IF TempSet < CurTemp THEN Lower

GOTO Display

Higher:

DIFF = TempSet - CurTemp/5

CurTemp = CurTemp + Diff

GOTO Display

Lower:

Diff = CurTemp - TempSet/5

CurTemp = CurTemp - Diff

Display:

LOW LED1

DEBUG DEC CurTemp,CR

IF CurTemp <> SetPoint THEN SkipBeep

DEBUG "AT SETPOINT!",CR,"!BELL",CR

HIGH LED1

SkipBeep:

PAUSE 250

GOTO Main

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Experiment #1: Flowcharting and StampPlot Lite

Questions and Challenge

1.List one everyday human process that involves a decision. List the steps in performing the process and the decisions needed to be made.

2.Develop a simple flowchart for the process in Question #1.

3.List an example of an electronics process in your home or school (such as that of an electric or microwave oven control, alarm clock, etc). Develop a simple flowchart to describe the process.

4.Develop the flowchart and code for the following process: The potentiometer simulates a temperature sensor. If the temperature exceeds 100 degrees, lock on the alarm (LED). Do not clear the alarm until the pushbutton is pressed.

5.Modify the program from Question #4 to use StampPlot Lite to display the temperature, alarm bit and status of the alarm.

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Experiment #2: Digital Input Signal Conditioning

Switches can provide control of an operation in three ways. One may be wired directly with the load and therefore control the full current and voltage. A switch also can be wired in the input circuit of a relay. In this case, the switch controls the relay’s relatively low power input and the output contacts control load power. The on/off status of a switch may also provide a digital input to a programmable controller.

How many switches have you used today? And, what processes were affected by the toggling of those switches? Table 2.1 lists a few possibilities, starting at the beginning of your day:

Table 2.1: Switch Possibilities at the Beginning of your Day

You are up to 15 switches and you haven’t even left your house!

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Experiment #2: Digital Input Signal Conditioning

Some of the switches listed in Table 2.1 probably have direct control of electrical continuity to the loads involved. For example, the bathroom light switch controls the actual current flowing to the vanity light bulbs. The thermostat is an example of a switch controlling a low-voltage system that controls a relay in your furnace or air conditioner.

Most of the switches in Table 2.1, however, probably are providing a digital high or low signal being monitored by an electronic control system. It is the status of this input signal that is evaluated and used to determine the appropriate state of the outputs involved. The snooze button isn’t physically opening the alarm circuit of your clock radio. When you “slapped” it, the momentary change of state was recognized by a programmable circuit. As a result, the program instructed the output to go off and add five minutes to the programmed alarm time. The start button on your microwave doesn’t have to carry the actual current that powers the magnatron, inside light, and ventilation fan. However, pressing it creates an input causing the oven’s microcontroller to close relays that do handle these loads.

Most often we think of switches as mechanical devices that make and break continuity between contact points in a circuit. In the case of the manual pushbutton and the limit switches pictured in Figure 2.1, this is exactly the case.

Figure 2.1: A Variety of Manual Pushbutton and Mechanical Limit Switches

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